# iTunes Sound Check: Any affect on sound quality?



## Joriarty

Just a quick question for you guys... does the iTunes "Sound Check" affect the sound quality at all, or does it just raise/lower the volume of tracks in the exact same manner the regular volume slider does? Or does it do some form of on-the-fly "brick-wall compression" as well?

 I like the idea of it, but I'm finding it hard to do a good comparison because it keeps... well... fiddling with the volume! 
	

	
	
		
		

		
			





 Thanks


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## Pangaea

It sucks, stay away from anything that itunes or ipods do that can effect equalization.


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## blessingx

Well stay away from presets anyway.


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## Joriarty

As I thought... I don't use equalisers at all, let alone *gasp* their "sound enhancer".

 Just wasn't exactly sure how it worked because manufacturers never explain that sort of stuff any more.

 Oh well. I've still got the volume button


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## Nocturnal310

It is really bad... it lowers your Sound quality apparently.

 Actually many people recommend to manually control the volume of your songs and not use sound check at all.


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## krmathis

Imo, yes it does.
 Tick the option and you will never get bit-perfect output from iTunes.


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## Oliver :)

As your search will have shown, you can buy iVolume (Mac & Win) if you desire a very convenient Replay Gain implementation that does not degrade the output. Soundcheck will have to be active for that but iTunes algorythm will not be used. I never looked back to the built-in option though, so if Apple radically improved it in the years passed that would have gone unnoticed. The - commonly regarded as negative - impact on sound quality used to be quite apparent, you can just give it a try if you wish.


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## Pangaea

I guess the way I look at it, unless you constantly listen in shuffle mode, just adjust the volume for each album you are going to listen to. With all the money we spend on gear, this 5 seconds of your time is worth it to get the most out of your bitrate.


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## pedxing

I seem to get much better quality output with with my iPod Nano when I used soundcheck compared to using the volume adjustment. The impact of sound check depends on the design of the hardware, drivers, and application.

 Some old threads about the iPod at hydrogenaudio said that soundcheck is applied late at the analog stage as a power adjustment instead of modifying the bits. Further up the pipeline, the equilizer modifies the data before the digital volume adjustment is applied. I wish someone can actually verify this and whether or not newer iPods behave the same way.

 The way I see it, its a balancing act between convenience, hot mixed recordings, and the quality of the output.


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## Pangaea

I suppose, but allowing the ipod or itunes to modify anything is a bad idea in my opinion. I used it on my shuffle when I go to the gym (only to keep it from blowing my ears off on some tracks) and basically about half the songs sound horrible and the other half sound normal.


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## blessingx

I understand a lot of the fears involved with manipulation, but everything from the near fanatical aim of bit-perfect output to left-over analog anti-EQ push around here sometimes is a bit much for me. They aren't the only concerns and are often not even the primary ones. We all take steps for convenience and you're going to get some manipulation along the digital/analog path (until we starting hearing digitally 
	

	
	
		
		

		
		
	


	




 ). Although I don't like iTunes implementation of volume management it's not because of it degrades the data path, it's because sounds bad. Same with the digital EQ. Although far from the best designed, if you stay away from the presets it can be of some use.


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## Pangaea

^ I agree with you completely. In fact I have had great luck with using custom built resistors for my headphones, and also implementing preamps. But in the context of what the OP is asking- sound manipulation by Apple, it is worth staying away from. And I am not talking about the multi band EQ that itunes employs because the OP is not. I am talking about the presets which sound check is. It is terrible and I base this on two points. One, Apple has historically jacked up EQ presets on every single one of its ipods/ itunes releases going back to the beginning. And two, I have used sound check, it is awful.


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## grokit

> Bumping an old thread, because I just looked up some information that confirms what I hear, and that is huge degradation with the enhancer and EQ, but none with sound check or crossfade. I think there are some mistaken assumptions here regarding sound check in iTunes.
   
  While the sound enhancer and EQ processing in iTunes is bad, crossfade and sound check are not. Sound check in particular gets a bad rap, mostly from the anti-iTunes crowd, but it's actually just a form of volume leveling, or audio normalization:
   
  "Specifically, normalization applies a constant amount of gain to the selected region of the recording to bring the highest peak to a target level, usually -0.3 dB, to allow for addition of two channels without exceeding 0.0 dBFS, or 100% (0 dB). *This differs from dynamics compression*, which applies varying levels of gain over a recording to fit the level within a minimum and maximum range. Normalization applies the same amount of gain across the selected region of the recording so that *the relative dynamics (and signal to noise ratio) are unchanged*."


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## chadbang

Thanks for the definite answer, Grokit. You are my hero, phew! That solves alot of worry!


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## grokit

Glad it was helpful, and thanks for bumping this thread because from what I understand the latest iTunes and iOS have FINALLY made some improvements to the EQ feature as well, reducing distortion by lowering the gain floor when equalizing. You should hear a drop in volume now when activating the EQ, that results in lower distortion when using it. I'm not sure yet if the enhancer has been affected, but it would make sense that it has because the enhancer is just a specific EQ curve anyways. This is great news for people that like to apply equalization (I'm not one of them). All they have to do now is allow custom EQ in the iOS devices, instead of just the pre-sets. Good job, Apple!


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## kryven

i disagree with gorkit, sorry gorkit 
after using apple lossless on my itunes, i do realize sound check really degrade the sound quality. better stay out of it.


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## sterling1

I find sound check is a great feature for playlists which will be played loud, as it restrains some tunes from being pushed into clipping or other distortions.


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## MerlinWerks

I'm reasonably certain ReplayGain and SoundCheck operate very much alike. You can even use MP3tag to convert RG values to SoundCheck values, I believe JRMC will also do this.


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