# I did a scientific test on a power conditioner--IT WORKS!!!



## Ferbose

I have briefly written about this before, when I reviewed Furman Power Factor Pro, but I guess not many people saw it. 
 Since the experience is truly interesting, I want to share it with more people.

 In my lab there is a scientific instrument amplfier, costing about $4000. It was state of the art about 4-5 years ago, and it is used to measure *pA* currents from single neurons. 

 Just how sensitive is this amplifier? 

 Suppose you have thinnest copper wire imaginable, made of *a sigle file of copper atoms* (such wire does not exist). Take 1 meter of this ultra-thin wire and attach it to a 1.5V battery, the current you get is about 1 pA.

 Another way to think about it. When a 10 cm wire is attached to the amplifier, it can detect the electromagnetic field generated by a person walking by, *even when the wire is placed inside a five-side shielded Faraday cage*. The cage is sitting on an air-stabilized steel table, with four shielding meshes on three sides and the top. Only one side is left as an opening so the experimenter can perform the work. Despite all this shielding, it can still detect the EM wave generated by a moving person. This is different from your body's interference with the indoor TV antenna. At home, a person is simply blocking an outside broadcast. In the lab, there is no EM broadcast. Instead, a walking person becomes the EM wave broadcast station. 

 As you can imagine, such super-sensitive amplifiers must have a superb power supply. In fact, you can't build an amplifier much more sensitive than this. Still, the amplifier has some internal noise. 

 One day we were just wondering if we can lower the noise floor of the amplifier. Normally, the amp is plugged into a cheap power strip. This is when I took my $229 Furman Power Factor Pro to the lab and plugged it in. To our delight, the amp's self-noise decreased about 30%, as seen on the oscilloscope. *Wow, we can SEE this thing really works!*

 As you can read in my review, everything I have plugged into Power Factor Pro sounds better, especially components with seemingly weak power supplies. Seeing that it can lower the noise of even one of the world's most sensitive instrument amplifiers, I am completely sold on this unit. It is no coincidence that Furman is a leader of power conditioning products for the pro audio market. Even their cheaper stuff _REALLY_ works. It certainly brought some improvement to a hi-end, ultra-sensitive scientific amplifier. If your home audio components are not as precision-made as some of the world's most sensitive scientific amplifiers, I am pretty sure Power Factor Pro will also serve you well.


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## gevorg

Thanks for sharing your finding, very interesting.

 Its no doubt that power conditioning makes a difference, the question is how audible it is, and if it is the best upgrade in a particular system.


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## JahJahBinks

very interesting finding, thanks.


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## shplorgh

Cool, good job! 
	

	
	
		
		

		
			





 But the "objectivists" will still find ways to blatantly ignore scientific proof.


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## felixkrull6

Ferbose,

 First off, great review. I like the fact that you actually added some science to your review.

 My only reservation is that I have to use an extension cord before I reach the point where I can use a power conditioner to plug in the rest of my gear. How do you think this will affect the conditioning? I don't think it will matter but I really don't know.


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## clarke68

Quote:


  Originally Posted by *hungrych* 
_But the "objectivists" will still find ways to blatantly ignore scientific proof. 
	

	
	
		
		

		
		
	


	


_

 

I doubt these stick-in-the-mud "objectivists" would ignore scientific proof, but they may ask, "proof of what?"

 Ferbose has demonstrated that the unit successfully reduces AC noise, which shows that Furman's engineers know what they're doing. However, marketing materials for the Power Factor Pro claim that the unit will "vastly improve your instrument amplifier's tone and clarity". 

 What will it do?

 "Improve your amplifier's tone!"

 How much?

 "Vastly!"

 These are subjective statements that can't be proven by an oscilloscope. Lots of things can be done to improve signal quality, but many of them don't affect any frequencies within the audio band.

 I'm not saying the Furman unit is one of these, and I'm not saying it doesn't improve the sound of audio systems...how would I know? I've never even seen one, let alone heard one. Ferbose likes it and he's got ears. All I'm saying is be careful where you point that "scientific proof".

 Ferbose: All that said, I really appreciate the efforts you put forth to test the unit...that kind of stuff makes Head-Fi a valuable asset to the audio enthusiast community. If I ever discover a need for power conditioning, I'll probably look no further than the Power Factor Pro.


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## Solude

I personally like power conditioners, see my sig... but not all conditioners are created equal and a lot of them fix things that aren't likely to be present in the first place 
	

	
	
		
		

		
		
	


	




http://www.hometheaterhifi.com/volum...et-4-2002.html

 This is a review of the PS Audio UO and to say it did nothing on the scope would be a large understatement. The PS fixes things that obviously weren't present at the reviewer's lab. So although the Furman worked great in that lab, that's not say it wouldn't be useless elsewhere.

 Again, I have a beast of a power rig, the trifecta conditioning, regeneration and surge protection. But without the scope I might just have a really big surge protector


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## edstrelow

Quote:


  Originally Posted by *clarke68* 
_I doubt these stick-in-the-mud "objectivists" would ignore scientific proof, but they may ask, "proof of what?"

 Ferbose has demonstrated that the unit successfully reduces AC noise, which shows that Furman's engineers know what they're doing. However, marketing materials for the Power Factor Pro claim that the unit will "vastly improve your instrument amplifier's tone and clarity". 

 What will it do?

 "Improve your amplifier's tone!"

 How much?

 "Vastly!"
_

 


 Showing a difference on an oscilloscope or by other measurement is at least a start to showing that a tweak is actually doing something. 

 Good psychphysical testing to assess how perceptible or meaningful such differences are is much more difficult than your average tweak sceptic realizes. For example it is easy to show no difference between two conditions if an experiment is badly set up, has poor equipment, subjects are not trained or whatever. In science, little stock is given to null results partly for these reasons. 

 I take the position that the human ear is incredibly sensitive and that a trained listener (including a golden ear) is likely to be able to detect, if only at a very low level of awareness, of many if not most things that can be measured in sound signals.


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## JahJahBinks

also how much coffee he had in the morning, too many variables to consider.


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## terrymx

Quote:


  Originally Posted by *felixkrull6* 
_Ferbose,

 First off, great review. I like the fact that you actually added some science to your review.

 My only reservation is that I have to use an extension cord before I reach the point where I can use a power conditioner to plug in the rest of my gear. How do you think this will affect the conditioning? I don't think it will matter but I really don't know._

 

seconded. say you use the power conditioner to your amps, but you use a regular cord for the power conditioner to the wall or regular cord from your p.c. to your amp. do you loose that special shielding and stuff.


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## slwiser

How would the Tipplight Omni1000LCD UPS for $99 at Costco compare with these units?


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## NotJeffBuckley

Quote:


  Originally Posted by *edstrelow* 
_I take the position that the human ear is incredibly sensitive and that a trained listener (including a golden ear) is likely to be able to detect, if only at a very low level of awareness, of many if not most things that can be measured in sound signals._

 

I agree that the human ear/human brain system is capable of detecting subtleties, and that if something is _significantly_ measurably different about the signal it's probable that the change is perceptible. My previous crusade against subjectvism on this board was aimed at the need to spend megabucks to get certain changes, not at tweaks in general. Objectivists aren't as one-dimensional as that guy seems to think


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## bigshot

I scanned through this thread and I didn't see any mention of the signal to noise rating on the amp with and without the conditioner. What is it? The noise decreased 30% of what?

 It's good that it does something, but without knowing how much it does... what can you say?

 See ya
 Steve


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## stryker

Anyone have any experience with this "power conditioner"? Yes, it's a _cable_, but it's really a power conditioner _within_ a cable.

http://www.sacdmods.com/SAPC-1.htm


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## Ferbose

Quote:


  Originally Posted by *bigshot* 
_I scanned through this thread and I didn't see any mention of the signal to noise rating on the amp with and without the conditioner. What is it? The noise decreased 30% of what?

 It's good that it does something, but without knowing how much it does... what can you say?

 See ya
 Steve_

 

All amplifiers have internal noise floor. You see the noise trace on the oscilloscope, and the up and downs got smaller after using the conditioner. If the internal noise is between -10 to 10 microvolts (arbitrary unit), now it looks like -7 to 7 microvolts. 
 Regardless of S/N ratio, if you lower noise floor by 30%, you increase S/N by 3 dB. 
 I actually went into the datasheet of the instrument amplifier and calculated its S/N to be 107 dB. Of course, this amplifier has a very special purpose (voltage clamping), which is very different from audio amplifiers, so directly comparing S/N numbers is not meaningful. 
 The point is, this is a state-of-the-art scientific equipment in its class a few years ago for extremely sensitive measurements. We can trust that it has an excellent power supply. The fact that it still benefits from a power conditioner is pretty remarkable, and convinces me that power conditioning benefits I heard are not just imaginations.


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## JohnFerrier

Quote:


  Originally Posted by *Ferbose* 
_All amplifiers have internal noise floor. 
 ... 
 Regardless of S/N ratio, if you lower noise floor by 30%, you increase S/N by 3 dB.
 ...
 The fact that it still benefits from a power conditioner is pretty remarkable, and convinces me that power conditioning benefits I heard are not just imaginations._

 

But I can't hear amplifier noise without power conditioning. What good does reducing it by 30%, 100%, or 500% do? If you hear noise without power conditioning, your system is not well designed. (Well designed doesn't mean expensive either.)


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## Ferbose

Quote:


  Originally Posted by *JohnFerrier* 
_But I can't hear amplifier noise without power conditioning. What good does reducing it by 30%, 100%, or 500% do? If you hear noise without power conditioning, your system is not well designed. (Well designed doesn't mean expensive either.)_

 

What you stated is a misconception. 

 Yes, the noise in your audio systems should be below your listening threshold. In other words, you should not hear speaker hiss at your listening position or hiss in your headphone. But once you play some signal through the system, the noise is added to the signal you hear. Say your signal is a smooth sine wave of 100Hz, and if you add a bit of 5000 Hz noise to it you start to see jagged curves. Even if your ear can not hear the noise by itself, your ear can hear the difference between a smooth 100 Hz sine wave with a jagged one. 

 Here is a real example. When you make a 24 bit recording and map it down to 16 bit, it is extremely apply dithering (noise shaping) to the last (16th) bit instead of doing simple truncation. Famous dithering algorithms include SBM (Sony), UV22 (Apogee) and K2 (JVC). Can you hear the single-bit signal (0000,0000,0000,0001=-96 dBFS) playing in your CD system? No, unless you turn volume way up. However, when this last bit is a part of the music averaging at -20 dBFS or so, it certainly can make a difference. If noise dithering is not applied to the last bit in CD, the result is harshness, and the loss of detail and spatial information. In fact, with proper noise dithering, you can extend the dynamic range of CD into 18-19 bit (a well known fact to mastering engineers). It is because humans can hear signals below the noise floor, a fact appreciated by LP lovers everyday. Despite the poor measured S/N ratio of LPs, the useful dynamic range is much larger than what S/N suggests, because we can hear signals buried within LP's analog hiss (especially because the noise in LP playback is non-random). In the early days of CD sales, dithering was not as advanced as it is today, and CD sound quality suffered. 

 You can't hear the digital 1-bit truncation noise being played alone, but it degrades the music you can hear. By the same virtue, even if you can't hear the analog noise of your amplifier without input, it can still audibly degrade your music when there is input. 

 Do I need to offer a simpler analogy? There are two pieces of white paper, but only one has some faint stain marks. When the room is very dark, you can't see any stain mark and you declare both papers are blank. With better lighting you start to see the difference, and you know which paper is cleaner.


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## PhilS

Quote:


  Originally Posted by *Ferbose* 
_
 Do I need to offer a simpler analogy? There are two pieces of white paper, but only one has some faint stain marks. When the room is very dark, you can't see any stain mark and you declare both papers are blank. With better lighting you start to see the difference, and you know which paper is cleaner._

 

Good analogy. Another one that might be appropriate in this context is when you look at a piece of white piece of paper and declare that it has no color in it. It's only when you compare it to a second piece of paper that is truly white that you see the slight color in the first paper. In other words, I didn't hear any noise in my system either until I did something that reduced it, and then I realized what I was hearing before.

 Another example of actual experience establishing that certain preconceptions may be misplaced.


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## Tim D

It depends...in my experience the noise can just be part of the noise floor (i.e. sits at the bottom), but it can also sit on top of your signal. Obviously the noise that sits on top of the signal is more harmful than a slight 3db rise in noise floor. But I would agree that if you have a ground loop or ground noise or other abnormality...its best to *remove* it entirely if possible. I had a ground noise problem that according to RMAA was only in the realm of 3-5 db, but I heard it as added grain while music is playing (that or you'd have to turn up the amplifier very loud to hear the slightly hashy noise floor). Noise that just sits under your signal would be like having a photograph with a few specks in the 'blacks', and noise that sits on top would be a photograph with a few specks anywhere and everywhere.

 I'd wonder about more tests such as testing at nighttime listening in a non-lab environment or different housing conditions, etc. Labs are typically full of high voltage test equipment, possibly large motors, etc. Are the power conditions in some subarb going to be the same as a New York apartment etc.


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## JohnFerrier

Quote:


  Originally Posted by *Ferbose* 
_What you stated is a misconception._

 

No it's not.

  Quote:


  Originally Posted by *Ferbose* 
_Yes, the noise in your audio systems should be below your listening threshold. In other words, you should not hear speaker hiss at your listening position or hiss in your headphone. But once you play some signal through the system, the noise is added to the signal you hear. Say your signal is a smooth sine wave of 100Hz, and if you add a bit of 5000 Hz noise to it you start to see jagged curves. Even if your ear can not hear the noise by itself, your ear can hear the difference between a smooth 100 Hz sine wave with a jagged one._

 

Noise that is inaudible without a signal is still inaudible with a signal.

  Quote:


  Originally Posted by *Ferbose* 
_Do I need to offer a simpler analogy? There are two pieces of white paper, but only one has some faint stain marks. When the room is very dark, you can't see any stain mark and you declare both papers are blank. With better lighting you start to see the difference, and you know which paper is cleaner._

 

You've turned this backwards. A power conditioner does not enhance the ability to hear as light enhances sight. If the stain is not visible, removing 30% of the stain does not make it more visible.


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## PhilS

Quote:


  Originally Posted by *JohnFerrier* 
_ A power conditioner does not enhance the ability to hear as light enhances sight. If the stain is not visible, removing 30% of the stain does not make it more visible._

 

 Are you theorizing, or or have you not had any success with power conditioners in terms of reduction of the noise floor?


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## JohnFerrier

Quote:


  Originally Posted by *PhilS* 
_Are you theorizing, or or have you not had any success with power conditioners in terms of reduction of the noise floor?_

 

I've got two $1,200 power conditioners in my room. Neither my wife or I could hear a difference.


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## PhilS

Quote:


  Originally Posted by *JohnFerrier* 
_I've got two $1,200 power conditioners in my room. Neither my wife or I could hear a difference._

 

Interesting. My experience was quite different, but perhaps my power is "noisy" or something.


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## Tim D

You can both be right. A water purifier could be considered worthless to someone who drinks pure water naturally. Additionally just because a power conditioner is expensive doesn't mean it is well designed either. The Furman unit is produced by a pro-audio/broadcast company and doesn't sell their gear in audiophile circles anyhow. If you are in the broadcast or pro-audio industry...you should probably be buying stuff that 'works' period.


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## JohnFerrier

Quote:


  Originally Posted by *PhilS* 
_Interesting. My experience was quite different, but perhaps my power is "noisy" or something._

 

A decently designed audio system will be designed not to have problems with line noise.


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## PhilS

Quote:


  Originally Posted by *JohnFerrier* 
_A decently designed audio system will be designed not to have problems with line noise._

 

That's a truism, I think, or it begs the question. Or maybe it's circular reasoning. But whatever.


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## JohnFerrier

Quote:


  Originally Posted by *Tim D* 
_You can both be right. A water purifier could be considered worthless to someone who drinks pure water naturally. Additionally just because a power conditioner is expensive doesn't mean it is well designed either. The Furman unit is produced by a pro-audio/broadcast company and doesn't sell their gear in audiophile circles anyhow. If you are in the broadcast or pro-audio industry...you should probably be buying stuff that 'works' period._

 

I don't know what is in the Furnman unit, but the ones I have use a 20 pound torroidal isolation transformer and rather large polypropylene capacitors.


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## JohnFerrier

Quote:


  Originally Posted by *PhilS* 
_That's a truism, I think, and it also begs the question. Or maybe it's circular reasoning. But whatever._

 

I know _you_ are confused.


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## bigshot

Quote:


  Originally Posted by *Ferbose* 
_I actually went into the datasheet of the instrument amplifier and calculated its S/N to be 107 dB._

 

107 db is about the volume of a car horn at close range. That means that you would have to have your music turned up pretty doggone loud to even get the noise floor to raise above zero. For all intents and purposes, a 30% improvement on 107 (or 104, depending on how you calculated it) is not discernable at normal listening levels.

 See ya
 Steve


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## PhilS

Quote:


  Originally Posted by *JohnFerrier* 
_I know you are confused._

 

Yes, you're too sharp for me. Good night.


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## Tim D

Quote:


  Originally Posted by *JohnFerrier* 
_I don't know what is in the Furnman unit, but the ones I have use a 20 pound torroidal isolation transformer and rather large polypropylene capacitors._

 

Well if it is 20 pounds of doing nothing, than it can continue doing nothing while shipped to be tested side by side to the Furman 
	

	
	
		
		

		
			





. Now *that* would be an interesting test.


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## bigshot

Quote:


  Originally Posted by *Ferbose* 
_Do I need to offer a simpler analogy? There are two pieces of white paper, but only one has some faint stain marks. When the room is very dark, you can't see any stain mark and you declare both papers are blank. With better lighting you start to see the difference, and you know which paper is cleaner._

 

Turning on the light is analogous to turning up the volume beyond 110 db.

 See ya
 Steve


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## Tim D

Quote:


  Originally Posted by *bigshot* 
_107 db is about the volume of a car horn at close range. That means that you would have to have your music turned up pretty doggone loud to even get the noise floor to raise above zero. For all intents and purposes, a 30% improvement on 107 (or 104, depending on how you calculated it) is not discernable at normal listening levels.

 See ya
 Steve_

 

That was in reference to a instrumental amplifier and not audio, and he already put a disclaimer saying that you couldn't really directly correlate it. In fact I'd suspect the 30% figure to be just a guestimate since you do not really know if it is a purely linear 30% improvement across the board in all conditions, etc.

 Again it depends on where the noise is. If you are talking about 104 vs 107, no one cares as it is both ear bleeding inaudible situations (or if negative reference to zero still inaudible). But within a reasonable loudness, 3db is just on the border of audibility. So if there is 3db of *hash* or grain sitting on top of your signal, it is easily audible to those with keen ears. Of course there are online hearing tests out there that debate on the definition of easily audible since apparently some people can't even recognize clearly out of tune notes.

 Also both aural senses and visual perception rely significantly on contrast. So maybe a 3db difference won't be noticable if both out of the audible range, but a 3db difference is audible if in the audible range. But no one I know can distinguish ultra-violet from infra-red either...

 I'm not saying everyone's system automatically must have a layer of hash or noise that will be removed with a power conditioner. I nipped my problem in the bud by removing a ground loop. Plus I never get a chance to do any listening except the dead of night where my line conditions are pretty optimal anyhow. And I'd also have to agree that better power supplies in audio equipment should come first (i.e. a crappy DC switching power supply on a clean main is going to have a worse output than a very good regulated DC power supply on a noisy main).


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## JohnFerrier

Ferbose, it was interesting that you are involved (some how) with the measurement of signals from neurons (and posted something about it). I'm interested in neuroscience and try to read about it when I can. Learn all you can.


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## Ferbose

Quote:


  Originally Posted by *Tim D* 
_It depends...in my experience the noise can just be part of the noise floor (i.e. sits at the bottom), but it can also sit on top of your signal. Obviously the noise that sits on top of the signal is more harmful than a slight 3db rise in noise floor._

 

The noise of the amp in the absence of signal can be called signal-independnet noise or self-noise. It is not going to go away when you have signal input. Suppose self-noise is 1 mV. When a 1 V signal comes in the output is going to be 1 V (+-) 1 mV, assuming voltage gain is 1. Every part of the noise floor is going to be superimposed on the signal. 

 It is also possible that amplifier has signal-dependent noise. If the 1V signal induces a noise of 5 mV in the amp. Then you are going to get 1 V (+-) 6 mV output. In other words, noise is never going away, but they just pile up higher and deeper.


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## bigshot

Quote:


  Originally Posted by *Tim D* 
_That was in reference to a instrumental amplifier and not audio, and he already put a disclaimer saying that you couldn't really directly correlate it. In fact I'd suspect the 30% figure to be just a guestimate since you do not really know if it is a purely linear 30% improvement across the board in all conditions, etc._

 

If that's the case then his measurements aren't measuring the right things. 3db of noise floor at 107db is great. A steady 3db of noise at all volume levels is a lousy amp, isn't it?

 See ya
 Steve


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## Tim D

There are two measurements that explain what I am talking about. Noise Floor measurements and S/N Ratio's. One is noise without signal and one is noise with signal. I am just saying poor noise floor is the lesser of two evils compared to poor S/N Ratio. If you had an amp that had a -90 db S/N Ratio and a -120 db Noise floor, and an amp that had a -96 db S/N Ratio and -96 db noise floor...I'm telling you right now the -96 db S/N ratio amp will be the clear winner in sound quality (well assuming the noise components in the first amp isn't easy on the ear harmonic distortion that is 
	

	
	
		
		

		
		
	


	




). That also is something to think about...amplitude or loudness is great and all, but the *type* of distortion is a huge factor in audibility. Noise that sits only on the floor (hence noise floor) and ignores signal for the most part is mostly of annoyance only to super sensitive IEM's...noise that sits on top (signal noise) is of annoyance for any headphone. Crappy power or ground noise can sound like hash and very grating. 2nd harmonic tube saturation would be the opposite.


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## Ferbose

Bigshot and John Ferrier, I think you misunderstand the audibility of noise itself vs. noise+signal. 

 Bigshot, you are right that hi-fi system does not go over 110 dB SPL (sound pressure level), which could cause permanent hearing damage. Now think about CD's 96 dB dynamic range. The last bit would be -96 dBFS (-96 db from full signal), meaning 14 dB SPL. A quiet room has noise level of 20-30 dB SPL, so you can't hear a -96 dBFS signal played through CD, at 14 dB SPL. But the truncation noise in the last bit of CD is definitely audible when the signal is -20 or -40 dBFS (normal music). This has been proven again and again by mastering engineers. That is wahy every digital mixer today has dithering. [Bob Katz's Mastering Audio has an excellent discussion on dithering] 

 Signal can make noise below hearing threshold audible. When signal is big and noise is small, you hear subtle changes to the signal. It also works the other way around: noise can bring out undetectable signal. If there is a signal too low to be heard, and you add a lot of audible noise to it, you can start to hear the signal. With big noise and small signal, you hear that the noise sounds funny and actually carries some signal. 

 For example, you cannot hear the difference between a 5 dB and 8 dB SPL signal. You hear just a quiet silence. However, you can hear the difference between 70 dB and 73 dB SPL--in fact 73 dB is twice as loud as 70 dB. Of course 3 dB difference in loudness makes a big difference. For loudness detection the ear can hear 0.1-0.5 dB difference. For noise detection, the ear is even more sensitive. It is thought that audio equipment should have >130 or >140 dB S/N to be considered noiseless (and hence 24 bit audio with 144 dB dynamic range). 

 Again a visual analogy. Suppose the reflection of moonlight is signal, and the shadow of a tree is noise. On most nights, you can't see the shadow created by the moon, because noise is below visible threshold and the signal is barely visible. When the sun comes out, the signal (relfected sunlight from the ground) is much stronger, and the noise (tree shadow) becomes so apparant.


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## Tim D

My sources may be out of date, but I believe the ear can hear differences of around 1db in good conditions. .1-.5db is a bit optimistic...that is like saying everyone can tell channel mismatches in volume pots or sources outright and confidently which is not true since a lot of equipment aren't even matched this well. 10 db is the 'perceived' doubling of loudness, 3db is the doubling of actual intensity. Course what the human ear can detect is really just a vague guestimate. I know a lot of people would have a very difficult time detecting a 3db bass boost if the bass is cleanly reproduced in both settings. Course throw in a distorted bass boost and it doesn't matter what level the boost is, you can probably hear the difference. However our ability to sense bass is not as keen as midrange...see there are so many variables at play. 

 But yes I would wager we can and do hear aggravating distortion in extremely minute amounts. A clean signal vs a minutely louder clean signal no. A clean signal vs a minutely dirtier signal yes.


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## JohnFerrier

Actually, the signal makes noise _more_ difficult to hear. Can you hear someone whisper in your ear better when it's quiet, or at a rock concert?


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## NotJeffBuckley

Quote:


  Originally Posted by *Tim D* 
_But yes I would wager we can and do hear aggravating distortion in extremely minute amounts. A clean signal vs a minutely louder clean signal no. A clean signal vs a minutely dirtier signal yes._

 

I'll cast my vote for this. I can hear intermodulate distortion of particularly high midrange sounds because my hearing, for some reason, is exceptionally sensitive to them. It sounds like a sharp, painful slice against the background of "good" treble. I've actually had occasion to test my difference threshhold for 3500Hz (a resonance point on one of my speaker systems' titanium tweeter), and even at +.5dB it's moderately ringing and painful. I have to turn it to -3dB at ~3500Hz if I don't want my ears to feel like they're being stabbed after a few hours of listening to anything with a lot of frequency presence in that region.

 However, in other speaker systems (particularly ones with silk- or paper-dome tweeters which lack that resonance), I can listen at the same average volume without equalization even though the drivers measure close to one another in linear frequency response; it's sort of a "sins of addition" versus "sins of subtraction" issue, I suppose. Subtraction, in the higher registers, sounds better to me.


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## Ferbose

Quote:


  Originally Posted by *bigshot* 
_If that's the case then his measurements aren't measuring the right things. 3db of noise floor at 107db is great. A steady 3db of noise at all volume levels is a lousy amp, isn't it?

 See ya
 Steve_

 

No, you misunderstand dB. dB is a relative measurement, not absolute. dB = 20 * log(V1/V2). If V1 is 10 times larger than V2, then the difference is 20 dB. dB is in logarithmic scale. For power, dB = 10 * log(P1/P2). 2V is 6 dB louder than 1V, but 2W is 3 dB louder than 1W. This is because P=IV=V^2/R. All audiophiles need to know this basic math about dB, seriously. When we say SPL=x dB, it means it is x dB louder than a reference we call 0 dB SPL. You can look up the actual sound pressure corresponding to 0 dB SPL if you like. Quiet rooms are generally 20-30 dB SPL. A super-luxury car is about 40 dB SPL when driving slowly. So 0 dB SPL is a very, very soft sound not normally audible. 

 If full signal causes the amp to output 10 V voltage swing, then -107 dB noise is 45 microVolts. Here the output is 10 V (+-) 45 microVolts (S/N = 107 dB). When signal is not as loud, say 1 V, the output is 1V (+-) 45 microVolts (S/N=87 dB). When signal is soft, say 0.01 V, the output is 0.01V (+-) 45 microVolts (S/N= 47 dB). When the signal is barely audible, say 1 miliVolt, the output is 1 miliVolt (+-) 45 microVolt (*S/N= 27 dB!!!*). Do you see how 107 dB S/N is not so great when you enter the softer passages of music? The *ambience* of that soft solo passage in a choral piece sung in a church is now *destroyed* by noise! 

 When the signal is zero or say something tiny like 100 microvolts, the output is 100 (+-) 45 microvolts (S/N=7 dB). This volatge is too small to move the speaker coils to produce an audible sound, and hence you think the noise is inaudible. But it is audible when there is actually music playing.


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## Tim D

Quote:


  Originally Posted by *JohnFerrier* 
_Actually, the signal makes noise more difficult to hear. Can you hear someone whisper in your ear better when it's quiet, or at a rock concert?_

 

Using a Rolling Stones concert at a concrete baseball stadium as an example. Crowd chatter = noise floor. The louder the PA the better the S/N ratio i.e. signal over the noise floor. Horrible reverberations and pockets made from concrete seating and overhang would be noise inline with the signal. You won't hear it unless there is a signal or music playing. Finally turning up the sound so loud and selling enough beer that you no longer care about noise floor or S/N ratio is usually the solution of choice 
	

	
	
		
		

		
		
	


	




. 

 A power conditioner could be like putting up acoustic treatment in a crappy venue. But if you were at a well designed acoustic venue, you wouldn't need it. You can never assume that power conditioners won't benefit other people's setup...that is like saying that all live shows will only be held at well designed venues...I wish.


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## JohnFerrier

Quote:


  Originally Posted by *Ferbose* 
_No, you misunderstand dB. dB is a relative measurement, not absolute. dB = 20 * log (V1/V2). If V1 is 10 times larger than V2, then the difference is 20 dB. dB is in logarithmic scale.

 If full signal causes the amp to output 10 V voltage swing, then -107 dB noise is 45 microVolts. Here the output is 10 V (+-) 45 microVolts (S/N = 107 dB). When signal is not as loud, say 1 V, the output is 1V (+-) 45 microVolts (S/N=87 dB). When signal is soft, say 0.01 V, the output is 0.01V (+-) 45 microVolts (S/N= 47 dB). When the signal is barely audible, say 1 miliVolt, the output is 1 miliVolt (+-) 45 microVolt (*S/N= 27 dB!!!*). Do you see how 107 dB S/N is not so great when you enter the softer passages of music? The *ambience* of that soft solo passage in a choral piece sung in a church is now *destroyed* by noise! 

 When the signal is zero or say something tiny like 100 microvolts, the output is 100 (+-) 45 microvolts (S/N=7 dB). This volatge is too small to move the speaker coils to produce an audible sound, and hence you think the noise is inaudible. But it is audible when there is actually music playing._

 

I can follow your numbers. You will more easily hear the louder signal. Noise is not easier to hear when competing with another signal. If you wish to believe so, then that is fine. What you write makes sense otherwise.


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## JohnFerrier

When you want to hear something interesting on the television, do you tell all your friends to start talking? Or do you tell them to be quiet?


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## Ferbose

Quote:


  Originally Posted by *JohnFerrier* 
_I can follow your numbers. You will more easily hear the louder signal. Noise is not easier to hear when competing with another signal. If you wish to believe so, then that is fine. What you write makes sense otherwise._

 

You still missed it. 
	

	
	
		
		

		
			





*Noise is easier to hear when signal is weaker*. S/N ratio is poorer when the signal is weak. Because amplifier self-noise is constant in voltage, not affected by the incoming signal. It maybe -107 dB relative to the loudest full signal on CD, but only -47 dB to a softer passage in the CD. 
*But a noise inaudible by itself can be made audible by a (weak) signal*. This is the beauty of our sensitve hearing. No, you don't really sense this small (inaudible when alone) noise as a separate entity. It is just that the distortion to the signal is audible (if you remove the noise the music sounds better), and hence we say the noise is audible. 

 Vice versa, a signal inaudible by itself can be made audible by adding noise. But this is unimportant in hi-fi, and only relevant if you try to receive/intercept minute signals. This is well proven in all kinds of sensory perception studies, even in fish. When you hear something interesting on TV, the signal is already audible. Hence, you don't need your friend to make noise. If they make noise the S/N will decrease, and you will be pissed. I can give you a real world example of noise making inaudible signal audible. Ever used an analog radio with tuning dials? There are some very distant stations whose signals are too weak to be audible. You tune into that frequency and you hear lots of noise but there seems to be a faint voice speaking underneath that noise, like eavesdropping on Martians. If you remove all that noise in the radio you *may* find that the signal is too weak to be heard (keeping the volume knob in the same position).


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## JohnFerrier

Quote:


  Originally Posted by *Ferbose* 
_You still missed it. 
	

	
	
		
		

		
		
	


	


_

 

No, you didn't make a point that I could miss.

  Quote:


  Originally Posted by *Ferbose* 
_*But a noise inaudible by itself can be made audible by a (weak) signal*._

 

You imagine so.

  Quote:


  Originally Posted by *Ferbose* 
_When you hear something interesting on TV, the signal is already audible. Hence, you don't need your friend to make noise._

 

Well turn the volume down until the television isn't audible. Now tell me how it becomes audible by adding another signal.


 .


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## Ferbose

I have come up with the ultimate example to bury this issue once and for all.

 Say you can hear the minimum of 30 dB SPL sound in your system, and let us suppose this corresponds to a -65 dBFS signal on your CD. And your amp's self-noise is constantly at 29 dB SPL when connected to a speaker and thus inaudible. Your CD has a soft passage at -63 dBFS, equal to 32 dB SPL in your system, and while this is playing your S/N is 3 dB, which sucks because noise level is 70% of your musical signal. When there is no signal, you can't hear the noise. When a soft music is playing, you say crap, I can't hear the ambience but only harshness. Now lower the noise floor of the amp from 29 dB to 26 dB SPL using a power conditioner, from inaudible to even more inaudible. When you play your -64 dBFS = 32 dB SPL soft msuic passage again, the noise is now only 50% of your music, and S/N is 6 dB. You ears will thank you.


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## JohnFerrier

If you turn the down the volume on a television until it isn't audible, how does the television become audible by adding another signal? It doesn't.


 .


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## Ferbose

Quote:


  Originally Posted by *JohnFerrier* 
_Well turn the volume down until the television isn't audible. Now tell me how it becomes audible by adding another signal.
 ._

 

Yes, some scientific facts are counterintuitive. 
 For example, that space and time are all relative, or something can be a particle and a wave at the same time. 
 But I can assure you that an inaudible signal can be made audible by adding random noise is a fact. You just need the correct, carefully controlled experimental condition to demonstrate it, and hence we have scientific labs set up to study human sensory perception. 
 As I said before, using noise to make sub-threshold signals detectable is irrelevant in audio. 

 But audio quality is hard to quantify by scientific methods so I am not a proponent of letting engineers and scientists telling us what sounds good. In fact, OP-amp designers at TI (Burr Brown) lets qualified listeners tell them what sounds good so they can design toward that direction.


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## JohnFerrier

Quote:


  Originally Posted by *Ferbose* 
_But audio quality is hard to quantify..._

 

I agree with this much.


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## Born2bwire

I pretty much agree with Ferbose here. Another way to think about what he is talking about is that the added signal acts as a carrier signal. The noise superimposes itself onto the signal and by doing so is raised up into our threshold of hearing. For example, if we turn the TV down until it is just below the threshold of hearing, and then add noise, the added amplitude of the noise plus the TV can be above the threshold.


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## JohnFerrier

Quote:


  Originally Posted by *U of GIBBERISH!* 
_I pretty much agree with Ferbose here. Another way to think about what he is talking about is that the added signal acts as a carrier signal. The noise superimposes itself onto the signal and by doing so is raised up into our threshold of hearing. For example, if we turn the TV down until it is just below the threshold of hearing, and then add noise, the added amplitude of the noise plus the TV can be above the threshold._

 

Got it.


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## markl

Someone said noise is *less* audible at loud volumes, but I disagree. It would seem to me (as a layman) that "noise floor" is variable with volume. If you listen to an analog recording, tape hiss (the "noise floor" of the recording) can be invisible at very low volumes, crank it up, and suddenly you have very loud hiss. You can hear this effect with your headphones when you crank your headamp to very loud volumes with no signal passing. The noise level increases with volume.

 Question:
 Another observation is that we seem to assume that this "noise" that was measured exists independent of the audio signal and is maybe only audible as extremely low-level background hiss (if it can be "heard" at all). But is he possibly measuring *distortion* which can affect the amp's ability to present sounds in the audible range? Perhaps the "noise" he measured can act on and contaminate the actual sound reproduced by the component? In that sense, it is also audible as distortion, and manifests as the perception of graininess, frayed edges, harshness, hash, etc. within the music itself? Possible?


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## JohnFerrier

Quote:


  Originally Posted by *markl* 
_The noise level increases with volume._

 

If the noise is from the source (CDP, tape player, etc.), then, yes, noise increases with the volume. I can't speak for every configuration, but any decent audio system today should not have audible noise with the volume turned up.


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## Beauregard

Just read through this thread and wanted to give a big thank-you to Ferbose! And the other folks who participated. For someone without a lot of technical competence, it's great to actually learn something worth knowing from an audio forum.

 This is exactly the sort of discussion I'd love to see more frequently - an informative bridging of the usually stereotyped objectivist-subjectivist divide.

 Much appreciated,
 Beau


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## Tachikoma

Quote:


  Originally Posted by *Ferbose* 
_Yes, some scientific facts are counterintuitive. 
 For example, that space and time are all relative, or something can be a particle and a wave at the same time. 
 But I can assure you that an inaudible signal can be made audible by adding random noise is a fact. You just need the correct, carefully controlled experimental condition to demonstrate it, and hence we have scientific labs set up to study human sensory perception. 
*As I said before, using noise to make sub-threshold signals detectable is irrelevant in audio.*_

 

This is the theory behind the "noise sharpening" plugin in foobar, isn't it? Correct me if I'm wrong


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## Ferbose

Quote:


  Originally Posted by *Tachikoma* 
_This is the theory behind the "noise sharpening" plugin in foobar, isn't it? Correct me if I'm wrong 
	

	
	
		
		

		
		
	


	


_

 

Here is a good link about dither:
http://www.digido.com/portal/pmodule...der_page_id=27

 If you want more information, Bob Katz's _Mastering Audio_ is a fantastic book.


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## Ferbose

Quote:


  Originally Posted by *Ferbose* 
_ using noise to make sub-threshold signals detectable is irrelevant in audio._

 

When I said this, I meant in the context of audio playback. 

 In audio playback, the goal is to minimize noise. There is no intent to inject noise so that sub-threshold audio signal can be heard. Although it is certainly feasible. Let me quote from Bob Katz's (the mastering engineer who made Chesky an audiophile label) book: "human beings are able to hear signals in the presence of noise of greater energy than the signal, i.e. with negative signal-to-noise ratios" (note: negative in terms of dB, as happens when 0<S/N<1). He went on to to explain that we can hear 15-20 dB into the noise. *Yes we can hear signal even when S/N=-15 dB.* 

*However, during digital recording, noise is added to make sub-threshold signal detectable more often than you think*. 

*In fact, every self-respecting 16-bit A/D converter today would intentionally inject an analog noise (~5 dB) into the signal before the actual A/D occurs.* Without doing this, CDs would sound pretty bad to audiophile ears. This process is called dithering. Although the codability of CD is 16 bit, or 96 dB dynamic range, its perceived dynamic range is close to 115 dB after proper dithering. Impossible? No, the only reason this works is because humans can hear signal below the noise. While you perform dithering in 16 bit A/D converter, the measured S/N becomes 91 dB, worse than the orginal 96 dB, but the perceived dynamic range greatly increases (115 dB). Without adding the noise prior to A/D, analog signals below the threshold of registering the last bit would be lost. The key is that the injected noise, when mixed with the incoming, sub-threshold analog signal, becomes a non-random noise that carries information which can be decoded by the ear-brain. _Dithering is not adding noise._ Dithering is encoding signals into the noise, and it only works because humans can hear signals below the noise. When there is no extra information to encode, adding noise just makes things worse. Dither is necessary in the analog domain during A/D (reducing quantization noise), and in the digital domain during the shortening of wordlength (reducing truncation noise) or computations (DSP). According to Bob Katz, dithering noise is almost inaudible only at -139 dBFS (got to admire our human ears). 

 When you have 20 or 24-bit A/D converter, injection of noise, or dithering, is basically unnecessary. The thermal noise of the equipment itself dithers at the 18th or 19th bit (self-dithering). Again, those bits beyond 19 is not useless: they still carry information because we can hear into the noise.


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## Ferbose

In the early days of digital audio, many audio professionals believed that quantization noise in 16-bit recording is irrelvant. Their logic was something like this:

_In a hi-fi system playing CD, the loudest signal (0 dBFS) should not produce an actual SPL of higher than 105 dB. Let us keep the volume knob constant so that 0 dBFS corresponds to 105 dB SPL. 
 Now, quantization noise is -91 dBFS, which would correspond to a 14 dB SPL signal. In a decent recording studio, ambient noise, or silence, could be 30 dB SPL. Therefore, quantization noise at 14 dB SPL is below hearing threshold by itself. If you play a bunch of 0000,0000,0000,0001 signals, you will hear nothing. If you make a 16 bit recording without dither, analog information below -96 dBFS is lost. They also thought it is OK, because the lost analog signal would correspond to <9 dB SPL, definitely inaudible when played alone. They therefore thought 16-bit digital audio was bullet proof and hence PERFECT SOUND FOREVER. 
	

	
	
		
		

		
		
	


	


_ 

 However, with soft music passages, the quantization noise superimposed on it becomes audible because of poor S/N ratio. In louder passages no doubt the signal will begin to mask the quantization noise. Undithered quantization noise at -91 dB turns out to be detrimental to low level ambience (decaying reverberation) information, and causes perceived harshness. To ovecome this, dithering is implemented and original analog signals below -96 dB to the peak, now cleverly encoded in noise, actually become audible, giving CDs a dynamic range of 115 dB. *In other words, without the help of noise, CD would never sound so good * It is neither a trick or magic, it is all because our brain can decode signal buried in the noise. It you dither too much, you destroy ambience, too. 
	

	
	
		
		

		
		
	


	




 So what does this have to do with power conditioning? Well, lowering the noise floor of your electronics is really important, even if you don't hear a noise when music is not playing. When music plays, those seemingly inaudible noises may cause audible degradations to the sound. Hence, you want to supress noise whenever possible. 

 The again, there are devices with magical noises that makes things sound better in some contexts, such as tubes. I read that there are tube analog equalizers that sound so good mastering engineers pass signal through it without equalizing band just to make the sound better. Whe mastering becomes largely digital, some people measure the noise of the magical analog compressor and use DSP to simulate it in digital compressors. Believe it or not, the biggest reason that digital audio can sound bad is its low noise. Lots of tiny but annoying artifacts become audible when the overall noise level is so low. In the analog age, these tiny artifacts are buried under the high noise of LP playback, but euphony is still achieved.


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## Edwood

Quote:


  Originally Posted by *JohnFerrier* 
_If the noise is from the source (CDP, tape player, etc.), then, yes, noise increases with the volume. I can't speak for every configuration, but any decent audio system today should not have audible noise with the volume turned up._

 

What is your system that you are using, from source to headphones?

 It is far easier to understand another person's point of view, when you know what configuration they are using.

 -Ed


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## Twombly

Quote:


  Originally Posted by *Edwood* 
_What is your system that you are using, from source to headphones?

 It is far easier to understand another person's point of view, when you know what configuration they are using.

 -Ed_

 

I would like to know what amplifier he's using as well, and also how he didn't go deaf testing this hypothesis. That's a lot for one man to sacrifice in the name of science.


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## PhilS

I guess the assumption is that we talking about "amplifier noise," right? If you are talking about noise from your power, it makes sense that a power conditioner could reduce that noise doesn't it?

 Also, I don't see why it is so difficult to grasp the concept that sometimes there is noise that you are not consciously aware of, but that you notice the elimination of noise when it is reduced or eliminated. For example, there was one occasion when I was listening to my IEM's in my car, and it sounded just fine, but then when took my phones out of my ear for a second to talk to someone and noticed the radio was on. I turned it off, put my IEM's back in, and the difference in sound was remarkable. The radio sound was not something I was actively hearing before I removed my phones, however. I have had similar experiences while listening to headphones while my wife is watching TV. I don't hear the TV at all, even if I listen for it and try to hear what is happening on a program that looks interesting, but several times when I have been sitting here withy my eyes closed, I have noticed immediately when she turned off the TV, or brought up an on-screen guide, which muted the sound. Thus, the notion that, if you can't hear noise or a noise floor, a reduction in noise or the noise floor will not be audible is not correct in my view. Just like you can't tell if you are looking at white or something that is absolutely clear until you see something that actually is 100% white or 100% clear in comparison. You might not think you are seeing fog or hearing noise until it is removed, right? Am I missing something?


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## JohnFerrier

Quote:


 Originally Posted by *Edwood*

 It is far easier to understand another person's point of view, when you know what configuration they are using. 
 

My POV is in agreement with Professor Rolleigh. Hope that helps.

  Quote:


 Originally Posted by *NotJeffBuckley*

 Dr. Richard Rolleigh, one of the world's leading physicists in the area of acoustic research...

 He told me to spend my money on the speakers, because that's the _only_ part of the system that has a significant effect on the sound in terms of dollar for dollar worth.


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## PhilS

"He told me to spend my money on the speakers, because that's the only part of the system that has a significant effect on the sound in terms of dollar for dollar worth."

 This is a value judgment. Note the words "only," "significant," and "dollar for dollar worth." His veiwpoint may be right for him. His viewpoint may also be right for others (although hopefully others don't take his judgments on blind faith but do their own listening or evaluation first). But his judgment may be absolutely, flat dead wrong, or of no persuasive impact whatsover, for others. And being a physicist does not necessarily establish that his value judgments are any better than any one else's. It may establish that they are more likely than not to be correct for those in HIS situation. And it may identify some of the important factors to consider. But "dollar for dollar" worth can vary by individual.

 P.S. Edwood, nice try re the "configuration." But you rarely get a straight answer to this question, for reasons I can never quite figure.


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## omedon

Quote:


  Originally Posted by *markl* 
_Someone said noise is *less* audible at loud volumes, but I disagree. It would seem to me (as a layman) that "noise floor" is variable with volume. If you listen to an analog recording, tape hiss (the "noise floor" of the recording) can be invisible at very low volumes, crank it up, and suddenly you have very loud hiss. You can hear this effect with your headphones when you crank your headamp to very loud volumes with no signal passing. The noise level increases with volume._

 

I don't see what you are getting at with the tape hiss as the "noise floor" of the recording. If you are playing a CD of an old jazz recording and it has tape hiss then that is not "noise" at all. It is every bit a part of the recording or "signal" as the trumpet.

 Am I missing something?


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## markl

Omedon, it's just an analogy for the phenomenon of rising background hiss you can observe when you crank your amp with no signal.

  Quote:


 If the noise is from the source (CDP, tape player, etc.), then, yes, noise increases with the volume. I can't speak for every configuration, but any decent audio system today should not have audible noise with the volume turned up. 
 

 This is very easy to test, just crank the volume on your headamp with no signal being passed. What do you hear? Rising levels of hiss. You can do the same with with your speakers and multi-watt amps. This is audible with the source turned on or off, it's coming from the amp itself. My gear is very high-quality, too. I've observed this phenomenon with every system/configuration I've ever owned, it's just a fact of life. The noise *is* there, it does rise with volume (if you crank it far enough). How audible is that noise when playing at regular volumes, or how much/little does it affect sound we can hear, and how much is that noise level affected by various forms of power conditioning/regeneration? Have no answers to those q's.


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