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level matching when comparing lossy to lossless
krabapple
post Feb 7 2013, 19:42
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I probably should have had this settled in my mind long ago, but -- how necessary is it to level match when you are comparing a lossless track, to its mp3 counterpart?

By way of investigation, I compared foobar2k's reported replaygain and track peak values for the same track encoded (LAME 3.98) as V2 (195kbps VBR) and at 320 kbps CBR

lossless:
Track gain -1.08
Track Peak 0.938171

195kbps VBR:
+0.11
0.954459

320kbps CBR:
+.10
0.934477

The track peak differences are negligable, but whence comes the >1db difference in RPG gain of lossless vs. lossy? Does this mean that one should level match according to those RPG values when doing an ABX?

This post has been edited by krabapple: Feb 7 2013, 19:42
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krabapple
post Feb 7 2013, 20:37
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Here's what I get when I run the three tracks through Audition 1.0's statistics generator (NB the mp3s were decoded by Audition 1.0's codec, which is Fraunhofer IIS mp3/mp3PRO)

(Sorry about the formatting -- i have never been able to recall how to get tables to format correctly in BB code).

The take home here is that the Average RMS Power is the same for all three. This is straightforward average level measurement (using a RMS Window of 50 ms). RPG, as I understand it, applies some psychoacoustics magic to come up with its recommended gain. I would expect the three files to differ *spectrally* and thus the algorithmic psychoacoustic prediction would be different?


CODE
Black Cow .wav Left Right
Min Sample Value: -30296 -30143
Max Sample Value: 29222 30742
Peak Amplitude: -.68 dB -.55 dB
Possibly Clipped: 0 0
DC Offset: -0.003 -0.007
Minimum RMS Power: -91.32 dB -85.37 dB
Maximum RMS Power: -9.34 dB -10.29 dB
Average RMS Power: -22.68 dB -22.37 dB
Total RMS Power: -21.18 dB -20.9 dB
Actual Bit Depth: 16 Bits 16 Bits

195VBR Left Right
Min Sample Value: -30151.38 -31275.73
Max Sample Value: 29373.31 30374.21
Peak Amplitude: -.72 dB -.4 dB
Possibly Clipped: 0 0
DC Offset: -0.003 -0.007
Minimum RMS Power: -91.67 dB -85.63 dB
Maximum RMS Power: -9.35 dB -10.3 dB
Average RMS Power: -22.68 dB -22.37 dB
Total RMS Power: -21.19 dB -20.91 dB
Actual Bit Depth: 32 Bits 32 Bits

320CBR Left Right
Min Sample Value: -30620.92 -30537.32
Max Sample Value: 29536.84 30406.43
Peak Amplitude: -.59 dB -.61 dB
Possibly Clipped: 0 0
DC Offset: -0.003 -0.007
Minimum RMS Power: -91.82 dB -85.46 dB
Maximum RMS Power: -9.34 dB -10.29 dB
Average RMS Power: -22.68 dB -22.37 dB
Total RMS Power: -21.18 dB -20.9 dB
Actual Bit Depth: 32 Bits 32 Bits


This post has been edited by krabapple: Feb 7 2013, 20:42
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Posts in this topic
- krabapple   level matching when comparing lossy to lossless   Feb 7 2013, 19:42
- - lvqcl   The difference between lossless original and LAME...   Feb 7 2013, 20:01
- - Garf   If they're encoded from the same source I see ...   Feb 7 2013, 20:03
|- - krabapple   QUOTE (Garf @ Feb 7 2013, 14:03) If they...   Feb 7 2013, 20:28
- - Arnold B. Krueger   QUOTE (krabapple @ Feb 7 2013, 13:42) I p...   Feb 7 2013, 20:12
- - greynol   QUOTE (Arnold B. Krueger @ Feb 7 2013, 11...   Feb 7 2013, 20:32
|- - krabapple   QUOTE I find there is too great a tendency to trea...   Feb 7 2013, 20:46
|- - greynol   QUOTE (krabapple @ Feb 7 2013, 11:46) But...   Feb 7 2013, 20:59
- - krabapple   Here's what I get when I run the three tracks ...   Feb 7 2013, 20:37
|- - db1989   QUOTE (krabapple @ Feb 7 2013, 19:37) (So...   Feb 7 2013, 20:59
- - greynol   Thanks for the data. I believe those average RMS ...   Feb 7 2013, 20:41
- - lvqcl   Do you have foo_hdcd or use foo_dsp_effect for de-...   Feb 7 2013, 20:48
|- - krabapple   QUOTE (lvqcl @ Feb 7 2013, 14:48) Do you ...   Feb 7 2013, 20:51
- - lvqcl   foobar2000 always uses postprocessing plugins such...   Feb 7 2013, 20:56
|- - krabapple   QUOTE (lvqcl @ Feb 7 2013, 14:56) foobar2...   Feb 7 2013, 22:23
- - greynol   Without going into a prolonged discussion about it...   Feb 7 2013, 21:03
|- - [JAZ]   QUOTE (greynol @ Feb 7 2013, 21:03) Witho...   Feb 7 2013, 22:57
|- - greynol   QUOTE ([JAZ] @ Feb 7 2013, 13:57)...   Feb 7 2013, 23:11
|- - Kees de Visser   For critical work I still prefer to adjust for equ...   Feb 8 2013, 11:24
- - db1989   foobar2000 uses libebur128 since v1.1.7, so a diff...   Feb 7 2013, 21:15
- - 2Bdecided   If I understand it correctly, EBU R128 / ITU BS.17...   Feb 8 2013, 13:06
|- - DonP   QUOTE (2Bdecided @ Feb 8 2013, 07:06) Bef...   Feb 8 2013, 14:18
|- - 2Bdecided   QUOTE (DonP @ Feb 8 2013, 13:18) QUOTE (2...   Feb 8 2013, 14:56
- - 2Bdecided   I do not use automatic (RG/R128) loudness matching...   Feb 8 2013, 13:15
- - greynol   I'm glad that is all spelled out, though you c...   Feb 8 2013, 16:58
- - 2Bdecided   It's made me realise that I ought to do a tabl...   Feb 8 2013, 17:56
- - lvqcl   QUOTE (krabapple @ Feb 7 2013, 23:28) QUO...   Feb 8 2013, 23:19


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