Mpc Quality Settings For Dolby 2.1 Streams, Is the default --quality 5 insufficient? Options

[atom]

Not sure whether this has been addressed before. Had a look through the forums, but could not find anything at first glance.

Something I picked up quite some time ago with MP3 was that the surround channel in a Dolby 2.1 (is that the correct term?) stream contained severe artifacts even with fairly high quality settings.

I experimented with MPC, and found this to also be true to for --quality 5. --quality 6 is significantly better, but I lack the equipment and expertise to truly compare the original with varying quality settings.

My question is: is this reasonable cause for encoding albums at --quality 6 or higher? In my opinion, yes. I have seen mention of other parameters (--ms?) that could possibly provide better stereo encoding (which is where the surround channel data really lives, isn't it?).

Can anyone maybe confirm my findings and comment on whether I'm just being paranoid, or whether it is more appropriate to use other parameters for such streams, in stead of --quality 6?

Note that many albums (especially live shows) seem to have this type of surround channel information; I believe it's either intentional or a side-effect of the way 2.1 decoding interprets the audio.

[user]

Adding --ms 15 in generally to --quality 5 ... 8 ?


I have encoded a test song with a lot surround informations, in different settings.
Well, it is a test song, which results to a higher bitrate than "average songs", I assume.
Here the bitrate increase is always neglectable.
As atom or somebody else told above, adding --ms 15, results to increases between 1% and max. 10%; so, for a better stereo image or surround image, people could add that switch.

So I suggest, to write this switch --ms 15 to recommended list of mpc settings (with remark about slightly increased filesizes), but only, if there are no other drawbacks, disadvantages.


The test:

CD Stereoplay Dolby Pro Logic 2 DPL2 Promo-CD
01.Pink Panther, Henry Mancini , Erich Kunzel & Cincinnati Pops Orchestra 2002
5732 samples, 2.29 min.sec
This song contains a lot surround info. Especially informations for
Logic7/DPL2 decoders. These informations are compatible to old DPL-decoders.

As Encoder I used actual recommended mppenc 1.14.

avr bitrate - filesize - setting (difference: kbit/s - Byte)

190.3 - 3,561,276 - --quality 5 --xlevel
190.9 - 3,572,708 - --quality 5 --ms 15 --xlevel (difference: + 0.6 - + 11,400)
221.5 - 4,144,888 - --quality 6 --xlevel
221.7 - 4,149,804 - --quality 6 --ms 15 --xlevel (difference: + 0.2 - + 4,900)
252.8 - 4,730,904 - --quality 7 --xlevel
252.8 - 4,732,108 - --quality 7 --ms 15 --xlevel (difference: 0 - + 1,200)
265.4 - 4,966,428 - --quality 7.5 --xlevel
265.4 - 4,967,360 - --quality 7.5 --ms 15 --xlevel (difference: 0 - + 1,000)
287.1 - 5,373,028 - --quality 8 --xlevel
287.1 - 5,373,868 - --quality 8 -ms 15 --xlevel (difference: 0 - + 0,800)
318.9 - 5,968,532 - --quality 9 --xlevel
318.9 - 5,969,068 - --quality 9 --ms 15 --xlevel (difference: 0 - + 0,500)
356.7 - 6,675,772 - --quality 10 --xlevel
356.7 - 6,675,772 - --quality 10 --ms 15 --xlevel (difference: 0 - 0) identical by bit to bit comparison.

Conclusion:

(well, I know, you should not draw conclusions based on one sample or song,
but this is "normal music" with surround-info, lasting 2.5 minutes. So it
contains different parts of music und should represent a kind of "average").

Only in q5 and q6 settings you have a minor increase of bitrates (+ 0.6
kbit/s !), comparing quality setting and same quality setting with added
switch --ms 15.
From q7 to q10 you can forget the bitrate increase at all.
q10 results to bit-identical output compared to q10 --ms 15.

So:
If --ms 15 does not have any other disadvantage regarding sound quality, I
would recommend to add --ms 15 to the quality settings, if you want more
precise stereo-image or keeping surround informations.
Because the bitrate increase is nearly neglectable, or below 10% (tested by somebody above).

Or do you have examples, where you experience worse sound quality, due to
added --ms 15 ?