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Advice please on converting m4a to ... ?, Needing some m4a files in a different format
MacEachaidh
post Jul 14 2011, 04:18
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I have an album of files that were given to me as m4a, which is a format my PMP won't play. They play fine in foobar2000, so there's no problem with the files themselves. foobar tells me they're AAC LC encoded, at 44.1 KHz and 130 Kbps.

Barring being able to get originals of the files in another format, I'll need to convert them. I realise that lossy formats will be degraded to some degree by conversion, but I'd like to minimise that if possible - except I don't know a great deal about formats and the consequences of different choices.

Would converting them to a lossless format like FLAC or APE (both of which my PMP can handle) limit the damage of transcoding? I'd appreciate any advice on the least damaging options to use.
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jupitreas
post Jul 14 2011, 04:36
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Would that be a Cowon device by any chance? Try renaming the files to *.mp4 and see what happens. Some Cowon players have unofficial support for aac.
If not, you'll need to transcode them. Why don't you simply get the ABX comparator plugin for foobar2k and do some blind tests? Convert the files to flac and to various bitrates of vorbis and mp3 and do a blind test. This is the best method to make sure you're satisfied with the sound quality of the conversion. Nobody here will be able to tell you what conversion settings are the best since it all depends on what you can hear.

This post has been edited by db1989: Jul 15 2011, 19:24
Reason for edit: no need to quote here; please take a second to delete unnecessary auto-generated quotations
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DVDdoug
post Jul 15 2011, 18:24
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QUOTE
Would converting them to a lossless format like FLAC or APE (both of which my PMP can handle) limit the damage of transcoding?
Yes. With lossless, there will be no additional damage. The "damage" is done during lossy encoding. The lossless file will sound identical to the M4A. The file has to be decoded when it's played-back or converted, and of course lossless encoding doesn't change the audio data.

Or, if you decide to convert to a lossy format (like MP3) using a higher MP3 bitrate should help, and you probably won't notice any difference in sound. (The only downside to higher bitrates is bigger files, but the files will still be smaller than the lossless formats.)
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greynol
post Jul 15 2011, 20:50
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To be clear, damage can be done during decoding as well.

Regarding transcoding to a higher bitrate, it may help, but it may not help. Temporal smearing is cumulative and generally unavoidable.

As per usual, whether these are audible is to be determined through proper double-blind testing.


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MacEachaidh
post Jul 16 2011, 01:02
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QUOTE (jupitreas @ Jul 14 2011, 13:36) *
Would that be a Cowon device by any chance? Try renaming the files to *.mp4 and see what happens. Some Cowon players have unofficial support for aac.

Hi Jupitreas, thanks for this. Yes, I'm using a J3, so I'll give what you're suggesting a try. If it doesn't happen to work, I'm no worse off, eh?

QUOTE
If not, you'll need to transcode them. Why don't you simply get the ABX comparator plugin for foobar2k and do some blind tests? Convert the files to flac and to various bitrates of vorbis and mp3 and do a blind test.

Good suggestion, thanks. I wasn't aware of such a plugin. To be honest, I'm just a listener, not a cognoscento (though I'm keen to learn what I don't know), so this will be an interesting experience for me. Thanks.

QUOTE
This is the best method to make sure you're satisfied with the sound quality of the conversion. Nobody here will be able to tell you what conversion settings are the best since it all depends on what you can hear.

Yes, good point, and I realised that in asking the question, but I thought there would be people here who knew about the technical side of this issue that I wasn't informed about.

Interesting you say "it all depends on what you can hear"; I said something similar as part of a question in my very first post here, and got an official warning - something I'm still a bit grumpy and shell-shocked about, to be honest. It seems logical to me that people favour the sound they subjectively most enjoy, and I asked the moderator how to say that within the bounds of this site, and was told there was no place for such sentiments on Hydrogenaudio. So I was aware in posing the OP of this thread that I didn't know how to ask such a question - even a blind listening test is going to be depend on my subjective hearing, isn't it? - but I'm still none the wiser in how to phrase it, or why an innocent question of mine was deemed so offensive.

Anyway, thanks for your help.

QUOTE (DVDdoug @ Jul 16 2011, 03:24) *
Or, if you decide to convert to a lossy format (like MP3) using a higher MP3 bitrate should help, and you probably won't notice any difference in sound. (The only downside to higher bitrates is bigger files, but the files will still be smaller than the lossless formats.)

Thanks for your advice, DVDdoug.

I figured this might be the case. I tried converting the files to FLAC via foobar2000 before I posted, but the files swelled from about 80MB to nearly 500, which was a little alarming! ;-) (You obviously anticipated that they would in your answer, so thanks.)

I'll check out jupitreas' suggestion first of renaming the extension and seeing if my Cowon J3 will play them, and if not try different bitrates of mp3.

My reason for posting in the first place was wondering if there were specific formats that might be less damaging to the files in transcoding than others - maybe something that was technically akin to the AAC format. But I appreciate your help.
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DVDdoug
post Jul 16 2011, 02:12
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QUOTE
Interesting you say "it all depends on what you can hear"; I said something similar as part of a question in my very first post here, and got an official warning - something I'm still a bit grumpy and shell-shocked about, to be honest...
Sorry you got treated harshly. Blind listening tests are subjective, but if done properly they are scientific. The point is to make sure you are really hearing a difference. On other "audiophile" websites, people make all kinds of silly claims, like speaker cables, and even power cables, making a difference in sound quality. And, sometimes we fool ourselves! The rules here help to prevent that sort of nonsense.

QUOTE
I figured this might be the case. I tried converting the files to FLAC via foobar2000 before I posted, but the files swelled from about 80MB to nearly 500, which was a little alarming! ;-)
biggrin.gif File size is directly related to bitrate (and playing time). Uncompressed CD audio has a bitrate of about 1411kbps, which means your 130kbps file is about 1/10th the size. With lossless compression, you can get files around 60% of the uncompressed size.
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greynol
post Jul 16 2011, 10:08
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QUOTE (DVDdoug @ Jul 15 2011, 18:12) *
people make all kinds of silly claims, like speaker cables, and even power cables, making a difference in sound quality.

How do you feel about a claim that iPods sound "plasticky"?

This post has been edited by greynol: Jul 16 2011, 10:14


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