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Wiki > Main > MasLimitations (compare)

Difference: MasLimitations (r3 vs. r2)

MAS Limitations

About

An extended test showed that the MAS MPEG audio decoders seems to not correctly decode all valid MPEG version/ layer/ bitrate combinations. This page is about the details. Problems do exist with MPEG2.5 layer 3.

These limitations usually don't affect music playback at all. Usually music does not use MPEG2.5, these low sample frequencies are aimed at speech compression.

However, there is one area where the MPEG2.5 limitations may hit - creation of voice files. The voice file size is limited to ~1.5 MB. As there are more and more entries added to voicing, there are 2 options to achieve higher compression:

  1. Lower the VBR quality setting (lame: -V <n> - increase n). With too low quality settings, this produces clearly noticeable compression artifacts.
  2. Lower the sample frequency (lame: --resample <n> ).

As soon as the sample frequency is lowered to 12 kHz, the MPEG2.5 playback problems may hit. When frame sizes of >64 kbit/s are used, dropouts occur. To avoid this, use the lame option -B 64 as well to limit the frame size. Avoid a sample rate of 11.025 kHz.

Detailed results

Legend

3507
MAS 3507D
other
MAS 3587F / MAS 3539F
S
Silent play
T
loud twittering noise

MPEG2.5 layer 3 Stereo

Bitrate 8 kHz 11.025 kHz 12 kHz
kbit/s 3507 other 3507 other 3507 other
8 DONEDONEDONEDONEDONEDONE
16 DONEDONEDONEDONEDONEDONE
24 DONEDONEDONEDONEDONEDONE
32 DONEDONEDONEDONEDONEDONE
40 DONEDONE S DONEDONEDONE
48 DONEDONE S DONEDONEDONE
56 DONEDONE S DONEDONEDONE
64 DONEDONE S DONEDONEDONE
80 S S S S S S
96 S S S S S S
112 S S S S S S
128 S S S S S S
144 S S S S S S
160 S S S S S S

MPEG2 layer 3 Stereo

Bitrate 16 kHz 22.05 kHz 24 kHz
kbit/s 3507 other 3507 other 3507 other
8..160 DONEDONEDONEDONEDONEDONE

MPEG1 layer 3 Stereo

Bitrate 32 kHz 44.1 kHz 48 kHz
kbit/s 3507 other 3507 other 3507 other
32..320 DONEDONEDONEDONEDONEDONE

MPEG2 layer 2 Stereo

Bitrate 16 kHz 22.05 kHz 24 kHz
kbit/s 3507 other 3507 other 3507 other
8..160 DONEDONEDONEDONEDONEDONE

MPEG1 layer 2 Stereo

Bitrate 32 kHz 44.1 kHz 48 kHz
kbit/s 3507 other 3507 other 3507 other
32* T T T T T T T T T T T T
48* T T T T T T T T T T T T
56* T T T T T T T T T T T T
64 DONEDONEDONEDONEDONEDONE
80* DONEDONEDONEDONE T T T T
96 DONEDONEDONEDONEDONEDONE
112 DONEDONEDONEDONEDONEDONE
128 DONEDONEDONEDONEDONEDONE
160 DONEDONEDONEDONEDONEDONE
192 DONEDONEDONEDONEDONEDONE
224 DONEDONEDONEDONEDONEDONE
256 DONEDONEDONEDONEDONEDONE
320 DONEDONEDONEDONEDONEDONE
384 DONEDONEDONEDONEDONEDONE

* These bitrates are forbidden for layer 2 stereo.

r3 - 05 Oct 2005 - 06:10:00 - JensArnold

Revision r3 - 05 Oct 2005 - 06:10 - JensArnold
Revision r2 - 20 Sep 2005 - 16:31 - JonasHaeggqvist
Copyright by the contributing authors.