MPC VBR flaws (low volume & ringing), audible under specific conditions Options

[guruboolez]

I’ve read recently some complaints about musepack and distortions occurring with classical music (examples here and here). There were no ABX tests to confirm them. According to my previous listening tests at ~175 kbps, musepack performs not only very well with various kinds of instrumental and vocal samples, but also better than competitors. But I’ve also noticed in the past one issue with this audio format that my previous test didn’t revealed, and it’s a very big one. I’d like to bring out this problem to the community, which wasn’t as far as I know warned about this kind of flaw.

Before carrying and before some seeing zealous users bare its teeth, I have to make clear that this issue only occurs in specific conditions. The problem is confined to low-volume musical content, and is mainly audible when this content has to be listened to a higher playback volume. In other words, affected tracks must have low volume parts, and tracks with high dynamic are not really concerned (you can’t constantly push the volume on such material: your neighbors won’t appreciate it). The problem becomes really critical with low-volume tracks only. People who have to live with the consequences of the “loudness war” are certainly not used to encounter such tracks, but for classical fans, tracks that are replaygained at +10 dB, +20 dB and sometimes +30 dB are all except a rare thing (tracks with corrected gain beyond +25 dB are nevertheless very rare). The encoded material would exhibit strong artifacts with ReplayGan set with Track Mode (they won’t be audible otherwise, except maybe as a subtle form of distortion – it could explain some recent complains about musepack and classical music). With RG enabled, even untrained people will be shocked by the terrible ringing that run across this musical material. MPC, with --standard profile, and to some degree --extreme and also –insane is apparently not sensitive enough to handle low volume situation.


At this stage of my account, some people would be probably tempted to claim that such issue is normal with perceptual encoding, and that all other formats will suffer from the same issue in this specific playback condition. But a quick comparison would immediately deny all validity to this idea. I’ve compared musepack --standard to comparable MP3, AAC and Vorbis presets, and these competitors showed the ability to encode properly (no ringing, flat lowpass at high level) the same material. Even stranger, MP3 at 128 kbps, or Vorbis at 90 kbps (!), or AAC (faac!) at 100 kbps perform *much* better than musepack --standard. In other words, perceptual encoders (at least modern one) could handle this situation transparently at mid/low bitrate, even with VBR; only musepack fails, and badly. It might be interesting to note that the VBR model is apparently flawed: with --standard, the bitrate drops to unusual value (110…140 kbps), and quality to an even more abnormal threshold. An illustration (graphical – listening tests were performed upstream - click for link) could make things easier to understand:



I’ve also uploaded an additional gallery - the last one looks very weird! and sounds even worse as it looks.


The ringing, and the austere lowpass, are obvious on these screenshots. Quality is objectively worse than MP3@128; subjectively speaking, the audibility is –as usual- linked to various conditions: hardware, player settings (RG or not), listener’ sensitivity to ringing. Some users won’t notice it, some others will be frightened. The important point to note here is that other audio formats have no problems; my purpose wasn’t to make an infertile comparison between MPC and other. Based on this comparison, I’m tempted to say that MPC could rejoin them with some tuning. Anecdotal point: LAME had recently serious issue (which also concern 3.90.3 ABR at mid/low bitrate) and they were recently solved by developers. I think Gabriel worked on an adaptive ATH threshold, and it might be a lead for MPC developer or for some users which are interested to play with current encoder switches.


I’ve uploaded some samples. The gain for short samples is necessary different from the gain of complete sample; but I’ve tried to cut sample with similar gain. The WavPack samples uploaded have all the native gain and the track_peak of the full track. I’ve also duplicated the track gain to the album gain.

http://guruboolez.free.fr/MPC/quiet_tracks_replaygained.zip

Two appendix in this zip file : a piano sample for which track gain for the sample doesn’t really match to the track gain of the full track (+40 dB instead of +25 dB) ; and a very noisy track for which musepack doesn’t have any problem, despite of high gain correction.


This report is probably the last one I’ll do for MPC (a developer have claim their lack of interest for improving classical at --standard), but I nevertheless hope it will help to improve the encoder. Playing with command line (in order to change ATH or noise sensitivity) might be enough to solve or reduce this issue; therefore, every MPC user could contribute. In the meantime, users should be aware of this issue.

This post has been edited by guruboolez: Jun 23 2005, 10:26

[Gabriel]

Isn't the purpose of track gain to be able to use the tracks in a compilation of tracks from different albums?
In this case, why would track gain be dependant of the gain of its neighbours tracks in the original album? If someone wants to listen a full album, he would use album gain, not track gain.

[Frank Klemm]

Isn't the purpose of track gain to be able to use the tracks in a compilation of tracks from different albums?
In this case, why would track gain be dependant of the gain of its neighbours tracks in the original album? If someone wants to listen a full album, he would use album gain, not track gain.

This is not an article about Musepack, but about flaws in the current ReplayGain
concept and implementation. Low level artefacts are related to this problem,
but this article is about ReplayGain and problems with ReplayGain. ReplayGain
ist *not* perfect at all, there's a long list of problems. Actually I use only
album based ReplayGain, other modes have a lot of problems which may significantly
reduce enjoy music.

Okay?

--------------------------------------------------------------------------------------------------------------

We should (always) start from the user application side.
And there there are at least three scenarios.

1. You want to listen to an album in original order. You want to remove volume differences between albums. The aim is to avoid volume differences between albums with different reference level, which is typical for album mastered in different decades. The effect is like a computer's turn on the volume control between albums (and by the way can also implemented in this way when the computer has access to the volume control via RS-232, RS-422, Cable LAN, Wireless LAN, IR-RC, IR-DA, USB, IEEE-1394, CAN, ...).

2. You want to listen to an album in original order. You want to remove volume differences between titels. The aim ist to reduce loudness differences inside an album, maybe also inside longer or very dynamic tracks. These loudness adjustments must be inaudible at all. No clicks, no distortions, no incredible noise boosting, no obviously loudness changes.

3. You want to shuffle titles of different album and you want to remove loudness differences between the titles. The goal is again: No clicks, no distortions, no incredible noise boosting, no obviously loudness changes.

Okay? Always start from the user application side, never start from the SSE and 3DNow!
assembler code side! Even when you like assembly programming on Intel.
Okay?

--------------------------------------------------------------------------------------------------------------

Now from the programmers geek side.

Solution for 1 is the album based replaygain and this work really great.

Solution for 2 is the proposal above. There should be a free parameter (with a useful default value) which controls the speed of the AGC. Someone want only slight loudness correction especially on title borders, another people wants to remove nearly all dynamic.

For album with silence at the title boundaries title based replaygain often works.
When there's only little loudness difference inside the album also the album gain works (see examples 2)!
There are some conceptional flaws and some flaws in the implementation.
* From time to time there are titles with (psychological) much too much title based replaygain gain
** short titles
** silent titles which must be silent at all
* file boundaries not at the real title boundaries
* live albums / classic without gaps
* noisy albums with little, but audible noise between tracks
* albums with DC
When an album has one of these problems, title based replaygain works poorly.
(see also Examples 1).

Solutions for 3 are also not so easy to implement. First of all we have problems with
boundaries (shifted, no silence). But it is not the task of replaygain to find useful
cuts or to fade between live titles during playback.

Primary goal is to remove loudness differences. Secondary goal is to avoid boosting
of intentionally silent titles. Third goal is to avoid noise boosting.

Short and very silent titles should not be boosted as much as replaygain's function GetTitleGain() says. This is important to avoid boosting of short and intentionally
silent titles.

To avoid noise boosting, ReplayGain's title gain must be limited. ReplayGain's album gain makes less problems, I only found albums with gains between -12.3 dB and +9,4 dB.
Within the title gain I found gain from -13,7 dB to +30,9 dB.

--------------------------------------------------------------------------------------------------------------

Even for 2 AND for 3 the current ReplayGain title gain is a really good implementation.
There are some flaws affecting the usage of ReplayGain title gain for problem 2 AND for problem 3. These should be fixed. In combination with a solution of the cut problem then ReplayGain title gain is also a great solution for problem 3.

Problem 2 must be solved completely different. Even when the ReplayGain title gain problems are solved, there are enough problems remaining when you want to use it
with music with
* file boundaries not at the real title boundaries
* live albums / classic without gaps
* noisy albums with little, but audible noise between tracks
* albums with DC

Examples: see next posting(s)

This post has been edited by Frank Klemm: Jul 9 2005, 15:23

[Frank Klemm]

Other examples where ReplayGain makes nonsense.
Especially the last example (May be someone knows this group and this album)
is suitable to destroy the hearing. While fading from "Waiting For The Worms" to "Stop"
the loudness is switched by more than 12 dB. The result are heavy overdrives for 2 or 3 seconds and you can frightens people to death.

CODE

decoding of file 'Back To Titanic (1997) -- [11] Celine Dion -- My Heart Will Go On (with dialogue from the film).mpc'
        to device /dev/audio (Open Sound System)

        Celine Dion: Back To Titanic    (1997)
   [11] My Heart Will Go On (with dialogue from the film)

 189.4 kbps,    4:43.09, SV 7.0, Profile 'Xtreme' (Beta 1.14), Gain 0.9616

    4:43.07 (runtime: 1.15 s  speed: 246.14x)

decoding of file 'Back To Titanic (1997) -- [12] Eileen Ivers -- Nearer My God to Thee.mpc'
        to device /dev/audio (Open Sound System)

        Eileen Ivers: Back To Titanic    (1997)
   [12] Nearer My God to Thee

 203.1 kbps,    2:22.34, SV 7.0, Profile 'Xtreme' (Beta 1.14), Gain 9.5280

    2:22.33 (runtime: 0.51 s  speed: 279.08x)

CODE

decoding of file 'Hot Rail (2000) -- [05] Crystal Frontier.mpc'
        to device /dev/audio (Open Sound System)

        Calexico: Hot Rail    (2000)
   [05] Crystal Frontier

 204.1 kbps,    3:56.77, SV 7.0, Profile 'Xtreme' (Beta 1.14), Gain 0.4222

    3:56.77 (runtime: 0.95 s  speed: 249.24x)

decoding of file 'Hot Rail (2000) -- [06] Untitled III.mpc'
        to device /dev/audio (Open Sound System)

        Calexico: Hot Rail    (2000)
   [06] Untitled III

 231.7 kbps,    4:07.48, SV 7.0, Profile 'Xtreme' (Beta 1.14), Gain 2.0893

    4:07.47 (runtime: 0.83 s  speed: 298.15x)

  17 Overdrives, maximum level 36659, rerun with --scale 0.89380

CODE

decoding of file 'Osho -- Kundalini Meditation (1995) -- [01] First Stage: 15 minutes.mpc'
        to device /dev/null (Null Device)

        Osho: Kundalini Meditation    (1995)
   [01] First Stage: 15 minutes

 233.3 kbps,   14:45.84, SV 7.0, Profile 'Xtreme' (Beta 1.14), Gain 0.5916

   14:45.83 (runtime: 2.83 s  speed: 313.01x)

decoding of file 'Osho -- Kundalini Meditation (1995) -- [02] Second Stage: 15 minutes.mpc'
        to device /dev/null (Null Device)

        Osho: Kundalini Meditation    (1995)
   [02] Second Stage: 15 minutes

 212.8 kbps,   14:39.18, SV 7.0, Profile 'Xtreme' (Beta 1.14), Gain 0.7464

   14:39.17 (runtime: 2.84 s  speed: 309.57x)

decoding of file 'Osho -- Kundalini Meditation (1995) -- [03] Third Stage: 15 minutes.mpc'
        to device /dev/null (Null Device)

        Osho: Kundalini Meditation    (1995)
   [03] Third Stage: 15 minutes

 215.7 kbps,   14:53.02, SV 7.0, Profile 'Xtreme' (Beta 1.14), Gain 1.1521

   14:53.00 (runtime: 2.69 s  speed: 331.97x)

decoding of file 'Osho -- Kundalini Meditation (1995) -- [04] Fourth Stage: 15 minutes.mpc'
        to device /dev/null (Null Device)

        Osho: Kundalini Meditation    (1995)
   [04] Fourth Stage: 15 minutes

   9.7 kbps,   14:42.02, SV 7.0, Profile 'Xtreme' (Beta 1.14), Gain 22.2075

   14:42.00 (runtime: 1.58 s  speed: 558.23x)

3425 Overdrives, maximum level 241085, rerun with --scale 0.13591

CODE

decoding of file 'The Wall (CD2) (1979) -- [10] Waiting For The Worms.mpc'
        to device /dev/audio (Open Sound System)

        Pink Floyd: The Wall (CD2)    (1979)
   [10] Waiting For The Worms

 200.2 kbps,    3:56.64, SV 7.0, Profile 'Xtreme' (Beta 1.14), Gain 1.3107

    3:56.64 (runtime: 0.85 s  speed: 278.40x)

decoding of file 'The Wall (CD2) (1979) -- [11] Stop.mpc'
        to device /dev/audio (Open Sound System)

        Pink Floyd: The Wall (CD2)    (1979)
   [11] Stop

 205.0 kbps,    0:34.95, SV 7.0, Profile 'Xtreme' (Beta 1.14), Gain 5.4828

    0:34.93 (runtime: 0.09 s  speed: 388.15x)

9937 Overdrives, maximum level 125247, rerun with --scale 0.26161

[Frank Klemm]

A lot of albums have nearly no differences between the title based ReplayGain values.
Using album based replay gain for equalization of titles may be the better choise.

CODE

       Title            |        Album            |
 Level-  |       (Peak+)|  Level-  |       (Peak+)|
Adjustment|  Peak (Adjst)|Adjustment|  Peak (Adjst)|  Filename
----------+--------------+----------+--------------+---------------------------
-2.32 dB | 34823 (26660)| -2.98 dB | 34983 (24823)| Islands -- [01] The Wind Chimes.mpc
-3.30 dB | 31059 (21241)| -2.98 dB | 34983 (24823)| Islands -- [02] Islands.mpc
-3.10 dB | 31613 (22124)| -2.98 dB | 34983 (24823)| Islands -- [03] Flying Start.mpc
-3.09 dB | 28675 (20091)| -2.98 dB | 34983 (24823)| Islands -- [04] North Point.mpc
-3.53 dB | 34983 (23300)| -2.98 dB | 34983 (24823)| Islands -- [05] Magic Touch.mpc
-3.61 dB | 30963 (20433)| -2.98 dB | 34983 (24823)| Islands -- [06] The Time has Come.mpc
-2.75 dB | 31731 (23119)| -2.98 dB | 34983 (24823)| Islands -- [07] When the Nights on Fire.mpc
         | 34983 (26660)|          | 34983 (24823)| --- maximum ---

CODE

       Title            |        Album            |
 Level-  |       (Peak+)|  Level-  |       (Peak+)|
Adjustment|  Peak (Adjst)|Adjustment|  Peak (Adjst)|  Filename
----------+--------------+----------+--------------+---------------------------
-8.00 dB | 36787 (14645)| -8.10 dB | 37953 (14936)| Wishmaster (2000) -- [01] She Is My Sin.mpc
-8.44 dB | 37953 (14363)| -8.10 dB | 37953 (14936)| Wishmaster (2000) -- [02] The Kinslayer.mpc
-8.06 dB | 36125 (14282)| -8.10 dB | 37953 (14936)| Wishmaster (2000) -- [03] Come Cover Me.mpc
-8.27 dB | 36675 (14153)| -8.10 dB | 37953 (14936)| Wishmaster (2000) -- [04] Wanderlust.mpc
-7.38 dB | 34621 (14802)| -8.10 dB | 37953 (14936)| Wishmaster (2000) -- [05] Two For Tragedy.mpc
-8.54 dB | 36245 (13559)| -8.10 dB | 37953 (14936)| Wishmaster (2000) -- [06] Wishmaster.mpc
-7.76 dB | 35925 (14702)| -8.10 dB | 37953 (14936)| Wishmaster (2000) -- [07] Bare Grace Misery.mpc
-8.43 dB | 35949 (13620)| -8.10 dB | 37953 (14936)| Wishmaster (2000) -- [08] Crownless.mpc
-7.22 dB | 35475 (15449)| -8.10 dB | 37953 (14936)| Wishmaster (2000) -- [09] Deep Silence.mpc
-8.02 dB | 35857 (14242)| -8.10 dB | 37953 (14936)| Wishmaster (2000) -- [10] Dead Boy's Poem.mpc
-7.90 dB | 35909 (14461)| -8.10 dB | 37953 (14936)| Wishmaster (2000) -- [11] FantasMic.mpc
         | 37953 (15449)|          | 37953 (14936)| --- maximum ---