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ALAC to wav, apply replaygain, back to ALAC?
brianhj
post Mar 3 2011, 00:12
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This has been asked before but I just want to confirm. Here's my situation.

I listen to my ipod in my car. My old alpine 9887 deck could read soundcheck information from itunes so all my songs had equal (or thereabouts) volume. All my music is stored as ALAC on the ipod. I'd like to keep it in a lossless format. I now have a pioneer p99rs, which is a much nicer deck but it seems to ignore soundcheck info.

So I'm considering taking my entire collection and converting to wav while applying replaygain album settings, and then converting back to ALAC.

Besides the obvious lossy side effects of normalizing a wav file using replaygain (some data lost due lowering of volume) is there ANY loss of quality besides the volume being lower/higher?
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UNHchabo
post Mar 3 2011, 01:32
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Well, unless you happen to lower the volume in amounts that corresponds exactly to a truncation of bits, you'll also have some quantization losses, similar to if you took some 48kHz music and resampled it to 44.1kHz.

If you keep an original lossless copy of your music on your computer, then I wouldn't worry about any potential quality losses, especially for in-car listening. If you are worried, ABX it.


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brianhj
post Mar 3 2011, 01:46
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ABX.. good idea. Yeah I'll just keep a backup! Haha such a simple idea. Thanks for the reply
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db1989
post Mar 3 2011, 02:20
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AFAIK, discussions here on that question have converged on the consensus that most Ďhardí normalisation is so unlikely to introduce audible degradation as to be Ďas close to lossless as lossy can beí. (In fact, pages were filled with debates over claims that itís so benign that it can be classified as lossless. yeahright.gif)

QUOTE (UNHchabo @ Mar 3 2011, 00:32) *
quantization losses, similar to if you took some 48kHz music and resampled it to 44.1kHz.
I donít mean to nitpick, and correct me if Iím wrong, but isnít quantisation confined to reductions in bit depth while altering sample rate is associated with different potential artifacts?
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UNHchabo
post Mar 3 2011, 17:24
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QUOTE (dv1989 @ Mar 2 2011, 17:20) *
I donít mean to nitpick, and correct me if Iím wrong, but isnít quantisation confined to reductions in bit depth while altering sample rate is associated with different potential artifacts?


You're right; I was mainly using that example as a means of describing the amount of quality loss involved (i.e., not much).

From what I've read, sample rate conversion seems to usually involve upsampling to the "least common multiple" of the two frequencies, then downsampling to the target frequency. Meanwhile, I'm pretty sure that volume reduction involves upscaling to a higher bit depth, doing the volume calculation, then downscaling back to the original bit depth.

Somebody please correct me if I'm wrong. smile.gif


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andy o
post Mar 3 2011, 22:51
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QUOTE (brianhj @ Mar 2 2011, 15:12) *
I listen to my ipod in my car. My old alpine 9887 deck could read soundcheck information from itunes so all my songs had equal (or thereabouts) volume. All my music is stored as ALAC on the ipod. I'd like to keep it in a lossless format. I now have a pioneer p99rs, which is a much nicer deck but it seems to ignore soundcheck info.

If you're gonna do this (which I presume would mean that your original unaltered lossless files will be backed up) then why not just encode to AAC or MP3 and apply mp3gain? I had the exact same problem with both my Pioneer home receiver and car receiver, and that was the easiest solution. There are programs that will automate it, like iGain.

BTW It seems the way Pioneer connects to the iPod via only a USB cable (which it seems manufacturers are calling "iPod Direct"), which is a digital connection, doesn't allow for Sound Check. As far as I know all products that required a proprietary cable, like your Alpine deck, are analog thus probably the same as the line out jack. Technically, your Alpine didn't read the Sound Check info, it was already output that way by the iPod.

It's really a bad oversight, since most manufacturers, including Alpine I think, are using this "iPod Direct" connection nowadays. Pioneer was just one of the first.

This post has been edited by andy o: Mar 3 2011, 23:02
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