MP3 vs. MPC vs. Ogg: Low volume test Options

[tigre]

Hi there!

Inspired by Using DirectSound SSRC Plugin thread I wanted to know what's the difference between outputs of foobar 2000 and winamp/other players. I figured out following test:

1. Take a sample (I did it with 30 seconds of music, could be done with test signals too), convert it to 32 bit resolution in Cool Edit Pro.

2. Apply logarithmic fadeout to the whole sample: 0 to -150 db (using CEP).

3. Save or dither to 24bit -> save, depending on the needs of lossy encoders (Step 4).

4. Encode with lame 3.90.2 -api, mpc 1.15i braindead, vorbis 1.0 -q 10 (this should not be the weak link).

5. Playback encoded files in tested players and capture output to wav file, resolution 24bit/96kHz if possible. The problem here is that I don't know any tool for this, I asked for advice in this thread. Because of this I've only tested this on foobar2000 0.5 beta so far, as its diskwriting feature is capable of 24bit/96kHz output. So until now it's not a player output comparison but a encoder comparison as you'll see soon.

6. Aply logarithmic fadein 0 -> +150db to the whole sample with CEP to bring the volume back to original level everywhere.

7. Listening to the resulting files.

The reason for this proceeding was to "exaggerate" the differences that occur at very low volume and make them audible.

My observations: All files started to contain aditional noise compared to the original after ~1/2 of playing time. At this point started what surprised me: The mp3 sounded like the original + increasing noise till the end of the sample while MPC and Vorbis started with slight artifacts and sounded more and more awfull: ogg somehow like underwater, mpc like NUMLock's lame audiophile preset and worse.

So is mp3 superior at low volumes? Not really. I gave mp3 an advantage by using CBR. A quick test using lame ape (=VBR) showed the same awfulness as Vorbis and mpc. Besides, I noticed that with decreasing volume the bitrate of all 3 codes decreased too.

Conclusion? I'm not sure, but maybe there's something that could be improved (adaptive ath model for high resolution signals, or ...). Imagine, you have a high resolution source (DVD audio ...) and music that uses its huge dynamic range (not completely of course) - and equipment with really high SNR ... this could be an issue.

I hope I haven't just wased my time and space on this forum . Thoughts welcome.

[SometimesWarrior]

I remembered hearing something about MPC SV8 having support for a higher dynamic range than SV7. A forum search turned up an old post by Frank Klemm mentioning this. Here's an excerpt (emphasis mine):

But the main advantage will be more stable quality than SV7. Especially the little bit too much treble problem should be fixed in SV8. Editing/Fading of files without reencoding is possible. You can convert SV7 and MP2 to SV8. Streaming is possible (but not optimized for weak connections). 32 kHz and 48 kHz is possible. Up to 7 channels are possible. Increases dynamic range (102 dB => 256 dB). Tagging support. CDdb (not lke cddb or freedb, but more like imdb).

Although perhaps the details have changed slightly; a newer excerpt from here says SV8 will "only" have 190dB possible dynamics.

I'm not sure if this has any relevance to your observations, it's just something that came to my mind. I'm fairly confident that the "increased dynamic range" goes towards eliminating clipping during the encoding phase, but I'm not sure if it also helps with the situation you're testing.