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M4A to MP3 320kbps
Deimuddi1955
post Jul 21 2012, 14:39
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Hello


i got some M4A audio files that i would convert in MP3's. Now my question is:


Is a M4A file with 256kbps the equivalent to a MP3 File with 320kbps. if it is so, can i convert the M4A File to a MP3 with a constant bitrate of 320 kbps? or should i convert it to the same bitrate of 256kbps??






thanks for answers rolleyes.gif rolleyes.gif rolleyes.gif
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mjb2006
post Jul 22 2012, 07:34
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@Deimuddi1955 - Encoding music to a lossy format will change the audio, no matter what settings you use. The m4a files are probably lossy already (if they contain AAC, not ALAC). The good news about lossy codecs is they are designed to fool you; probably you won't notice the audio is changed, unless you use some of the lowest settings. So as Porcus implied, it would be wasteful to use higher settings than the minimum needed to not notice. 320 kbps would be very wasteful. Probably you will not hear the difference even at 128 kbps. Try it and see.

Listening tests have shown that people generally stop noticing the difference between the original and the lossy version at bitrate n for MP3 and at bitrate n-minus-something for AAC. But you shouldn't infer from that "if I decode 256 kbps AAC and re-encode it as 320 kbps MP3, it will be the same quality." It's the same quality if you can't tell the difference. If you can't tell the difference between the AAC and the content transcoded to 128 kbps MP3, then it's highly likely the transcoded material at all MP3 bitrates from 128 to 320 is the same, maximum quality.

Also consider if the 256 kbps AAC has some content (or noise) that it's preserving in the 16+ KHz frequency band. This content/noise may be beyond what you can actually hear in actual music, so it's wasting space in the file. AAC also happens to be much better than MP3 at handling content in that uppermost band. The MP3 encoder at 320 kbps may try a bit too hard to keep that content without messing it up too badly, thus sucking away precious bits from the lower bands that you can hear. But at a lower bitrate, the MP3 encoder may ignore that high-frequency content (or noise) and might produce better quality for you in the more-important lower bands.

This post has been edited by mjb2006: Jul 22 2012, 07:36
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DevilMind
post Aug 23 2012, 10:44
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QUOTE (mjb2006 @ Jul 22 2012, 11:34) *
@Deimuddi1955 - Encoding music to a lossy format will change the audio, no matter what settings you use. The m4a files are probably lossy already (if they contain AAC, not ALAC). The good news about lossy codecs is they are designed to fool you; probably you won't notice the audio is changed, unless you use some of the lowest settings. So as Porcus implied, it would be wasteful to use higher settings than the minimum needed to not notice. 320 kbps would be very wasteful. Probably you will not hear the difference even at 128 kbps. Try it and see.

Listening tests have shown that people generally stop noticing the difference between the original and the lossy version at bitrate n for MP3 and at bitrate n-minus-something for AAC. But you shouldn't infer from that "if I decode 256 kbps AAC and re-encode it as 320 kbps MP3, it will be the same quality." It's the same quality if you can't tell the difference. If you can't tell the difference between the AAC and the content transcoded to 128 kbps MP3, then it's highly likely the transcoded material at all MP3 bitrates from 128 to 320 is the same, maximum quality.

Also consider if the 256 kbps AAC has some content (or noise) that it's preserving in the 16+ KHz frequency band. This content/noise may be beyond what you can actually hear in actual music, so it's wasting space in the file. AAC also happens to be much better than MP3 at handling content in that uppermost band. The MP3 encoder at 320 kbps may try a bit too hard to keep that content without messing it up too badly, thus sucking away precious bits from the lower bands that you can hear. But at a lower bitrate, the MP3 encoder may ignore that high-frequency content (or noise) and might produce better quality for you in the more-important lower bands.


well i want to convert my 320kbps mp3 (CBR & VBR V0 ) to 128kbps m4a Nero AAC-LC CBR to save disk space.

so will 2 pass in Nero AAC-LC will help keep the quality?

This post has been edited by DevilMind: Aug 23 2012, 10:46
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