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M4A > WAV > M4A/MP3. How bad?, Was: don't flame me please!
post May 30 2006, 16:19
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i had some .m4a files, i decided i wanted to go back to .mp3 (long story) so i converted them to .wav with the intent of converting them to .mp3 (a sin, i know) and now i want to convert them back to .m4a

my question is... if one were to convert an m4a file to a wav file and then back to an m4a file would there be a loss in quality? (probably yes) if YES, would it be a SIGNIFICANT loss in quality? as in if the music i'm talking about is classical music originally encoded at 192, would it sound icky after decoding and re-encoding?

i'm a little new to the world of codecs and encoding and the inner workings of it all, so this might be a stupid question, i apologise in advance!

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post May 30 2006, 16:27
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The answer you'll get in these forums is that a) there is a loss in quality, and b) you could check it by yourself if it is significant (significance depends on the subject and material)

I am unsure if you ask about converting m4a->wav->mp3->wav->m4a or just m4a->wav->m4a. I am quite convinced that on the first case, you would hear the artifacts added by the process.
If it is m4a->wav->m4a, you might not hear it, but depends on several factors (encoder used, settings, between others).
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post May 30 2006, 16:34
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As Jaz has stated, it depends on you. Personally, I can hear a difference between lossy transcoded files made from lossy sources. Adding the extra step of converting them to wav, then back to lossy doesn't add any quality, it is the same as going straight from m4a to mp3 instead of going from m4a->wav->m4a.

It all depends on your hearing ability, the equipment you are using, and your listening environments. Download foobar2000 and conduct a ABX test on the source m4a files (or the wav files) and the transcoded m4a files.
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post May 30 2006, 18:41
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Transcoding artifacts seem to vary a great deal depending upon codecs and settings. As an example, I have found the following to be true:

1. Transcoding from large MP3 (e.g., large VBR LAME files) to 128kbps AAC (iTunes) actually works quite well with few audible artifacts. I have done this often to pack more songs on small devices like an iPod Shuffle and been pleasantly surprised.
2. Transcoding from large AAC (e.g., 192kbps iTunes AAC) to 128kbps AAC (iTunes) reliably produces audible artifacts. Nasty!
3. Transcoding from AAC (any bitrate) to LAME MP3 VBR (-V 2 to -V 5) works remarkably well with respect to artifact generation.

There are obvious inconsistencies here, but the upshot is that only experimentation can determine how audible the effects of transcoding will be.

One may ascertain from the very short results above that transcoding from high to low bitrates with the same codec causes problems, but this would require more time that I have to test.
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