mp3/m4a compression help needed

[rachmiel]

does anyone have enough experience with the subtleties of audio compression to be able to explain *in your own words* (i.e., not paraphrasing an online article, but speaking from your own experience) what kind of degradation happens to audio when it is compressed into mp3 and m4a formats?

- what happens to the dynamic range?
- what happens to the frequency spectrum?
- how much noise is introduced?
- what "tricks" do mp3/m4a compression use to get a sexy sound?
- how close is a 128-kbps stereo mp3 to the uncompressed original?
- ditto for 160-, 192-, 256-, 320- kbps?
- is there a better (quasi-universal) compression format to use for audio?

and so on.

thanks in advance everyone.

rachMiel

[Jeremy_NSL]

Easiest just to get a copy of LAME or iTunes and experiment. Compress some .wavs to 64, 96, 128, and 192 bitrates and listen to them.

For me its very obvious anything under 128kbps is lower-samplerate and chorusy. Depending on the material I can pick out mp3s at higher bitrates due to: distortions, flanging, mushy attacks, stereo imaging problems. Properly encoded vbr mp3s almost never bother me much though.

I don't use mp4 because my portable and car stereo can't play it. So I can't advise on that format. Also there is the free ogg format which is pretty good at low bitrates.

For more info, check out www.hydrogenaudio.org
All of your questions can be answered there, probably just by searching the forum for past posts.

I used to hang out there alot (about 800 posts I think), but in the end I decided LAME --alt-preset standard vbr mp3s sound good enough and I don't really need to dick around with new formats, versions etc. Good luck!

[Sicklecell666]

Random ( ) thoughts:

LAME is the MP3 encoder of choice according to everyone I've asked about it.

128kbs is the internet standard and going beyond it will discourage potential listeners who are on dial-up modems.

MP4 sounds pretty good, but the two click rule prohbits 98% of your target audience from listening to it cause that's an extra codec that must be located, downloaded & installed. In the face of that, the instant gratification of listeniong to a track in one click falls to the wayside somewhat.

Ditto for .Oog, but oog is way less destructive to the source audio than mp3.

They all suck. I wish we'd just reach the next cieling on ISP speed and HD size so we didn't have to worry about compressing files at all..

[rachmiel]

thanks, everyone, for your help.

rachMiel

[kuniklo]

thanks, everyone, for your help.

rachMiel

For exhaustive discussion and debate on this subject go to http://www.hydrogenaudio.org

The short version of the story is:

1. lossy codecs throw away as much of the source sound as possible without introducing artifacts, especially higher frequency components

2. mp3, ogg, and m4a all can achieve transparency at around 192-224kbits/sec on most material for most listeners

3. at lower bitrates good m4a and ogg encoders outperform mp3, but at higher bitrates they're all very close

[Lunatique]

Hydrogenaudio has all the answers. I've decided for myself to:

1) Use FLAC for lossless encoding. I burn these to DVDs for archiving.

2) Use LAME Alt Preset Standard for lossy encoding to listen to from my hard drive or portable device.

I agonized over whether to use Monkey, Wavpack, or FLAC for lossless compression. I did a lot of research and posted polls at hydrogenaudio. Turned out FLAC is the clear choice.

I agonized over whether to use Musepack or LAME for lossy compression, and realized that for maximum compatibility and practicality, LAME can't be beat. Also, I ABXed many examples and cannot hear the difference between the two at comparable files sizes, nor could I hear the difference between the lossy version and the original wav file. I think except for highly unusual cases, alt preset standard is transparent to human ears.

[Churchy]

i dont think 128kbps is the internet standard anymore; it seems to have jumped up to 192kbps, thankfully

usually i can hear the effect of 128kbps, but not 192kbps

[kuniklo]

i dont think 128kbps is the internet standard anymore; it seems to have jumped up to 192kbps, thankfully

Also, you'll get better results with lame if you use --preset standard, which gives vbr bitrates around 192kbps, than you will if you force 192kbps.

[kuniklo]

Ditto for .Oog, but oog is way less destructive to the source audio than mp3.

This really isn't true if you're talking about lame mp3s. Lame at higher bitrates is very competitive with ogg vorbis. Vorbis does have other advantages though, like a sane tag format, gapless playback support, and free licensing.

Vorbis is better at sub 128kbps rates.

[Lunatique]

If you want uncompromised lossy compression, look no further than Musepack. It is the defacto standard that audiophiles use to judge for highest lossy encoding quality. (But if you're going to encoding at lower bitrate anyway, then it makes no difference. IMO, no one should be encoding at low bitrates unless you LIKE having horrible compression artifacts in your music.)

[kuniklo]

If you want uncompromised lossy compression, look no further than Musepack.

Musepack is the best, but it's not very widely supported yet, unfortunately.

[smart]

aac sounds a bit better than mp3 to my ears, but it wont play on my boombox or car stereo like mp3 will.

I usually encode mp3s at 256 to go in the car, but 192 sounds ok to me. 128 mp3 doesn't sound that bad at all, it just doesn't sound as dynamic to me.

it's probably all just placebo though to be honest. maybe i just like the number 256

[kuniklo]

aac sounds a bit better than mp3 to my ears, but it wont play on my boombox or car stereo like mp3 will.

There are large placebo effects in audio compression comparisons. If you really want to compare codecs you should do some double blind testing. You might be surprised by the results.

[smart]

wow. i just edited my post to say it's probably placebo, and after i finished i saw you had posted that, telling me the same thing.