Ciao !

I need to compress some music from the soundtrack of DVDs: a lot of live recordings. unavailable on audio cd...

I converted from AC3 to WAVE: stereo, 48khz, 16 bit.

ONLY ABOUT QUALITY: is better compress a 48khz mp3 or downsample from 48 to 44.1, before the mp3 compression, using Cool Edit ???

I know AC3 is a lossy format: can a second lossy compression from ac3 to mp3 sound bad ? Or is this mp3 sonically as good as the wave ?

And what about file size ?


Thank you !

Hi pecosbill76,

If you want to burn the tracks as an Audio-CD, downsample them to 44.1KHz. If you don't, leave them as 48KHz.

And yes, any lossy format transcoded to another lossy format (AC3 > MP3), or even if it is decoded to a lossless format before being encoded to another lossy format (AC3 > WAV > MP3); it will lose quality. Thus transcoding is not recommended. However, the quality loss may not be audible to you, so in the end, it /is/ your decision.

File size...well, uncompressed WAV takes up alot of space as opposed to the original AC3 or MP3, so...you have four options:

1) Keep the original AC3 files straight off the DVD.

2) Keep the decoded PCM (WAV) files (and the disk space usage they bring).

3) Encode the decoded PCM files with a lossless compressor such as FLAC or Monkey's Audio. You'll shrink the files a bit, but they will still take up substantial diskspace; however, you will retain the quality of the original AC3 files (unless you have edited them in the PCM stage).

4) Transcode to MP3 (not recommended), however, depending on the settings you use (--preset standard is recommended), you will end up with files that will consume considerably less disk space than the above.

Hope this helps.

Feel free to point out any errors that I may have made.

If you plan to encode to MP3 with Lame you should downsample to 44.1 kHz before encoding, since Lame is only tuned for this sampling frequency. 48 kHz works with Lame, but you will most likely get worse results (quality wise).

OK, I didn't know that one. I thought LAME could take either sampling rate and convert with the same quality. Just follow his advice

Well if you feed lame with a 48 kHz wavefile it will encode it as 48 kHz, which is not optimal quality when it comes to Lame. You can also force Lame to downsample internally to 44.1 kHz, I think you can do that with the -resample switch. Theoretically downsampling with Cool Edit should be better.

A good transcoding tool (not only for ac3) is BeSweet, it can use a high quality resampler named SSRC (which is especially good at 48 -> 44).

Homepage: http://dspguru.doom9.net/

Always use the latest beta (!) and also download the GUI for the sake of convenience...

That's the best advice. You can downsample and transcode all in one hit.

Keep in mind that if the source is stereo AC3 then transcoding to lame -aps will probably give you bigger files, since stereo AC3 is usually 192kbps and in rare cases 224kbps. So you might be better off by just keeping the original AC3's.

If the source is 6ch then you can downmix to 2 channels using dolby pro logic or dolby pro logic 2 or just a stereo donwmix and you can encode that to lame, vorbis, mpc...whatever. You will certainly gain some space since the 6ch AC3 files are usually 384 or 448kbps but you will need a dpl or dpl2 compatible decoder to listen to the surround information. Most of these things can be done with besweet. Give it a try.

If everybody here says that lame is optimised for 44.1kHz who am I to argue? But I don't think this is the case with vorbis or mpc. Correct me if I'm wrong.

regards
echo