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Subject: Unlocking the full features of the MAS chip (long, sorry)
From: Brent Geery (fasttimes_at_mochamail.com)
Date: 2003-04-28


I'm not a programmer, but I can read a datasheet. :) After taking
another look at the MAS datasheet, I've noted several features that
have not yet been implemented as user configurable options. I'd love
to have as much control over the MAS as possible, and use it to full
capability. I'd especially like to know from programmers, if any of
the following is not possible (even though the MAS datasheet says it
can do it) because of limitations of Archos' implementation.

Recording issues first.:

Add ability to disable/enable CRC protection -
From what I understand, this is enabled and there is no way to disable
it in the menus. I personally do not like using CRC, as much
software/hardware will just ignore them anyway! CRC protection is
controlled by bit 8 of MAS register address D0:7F0 (1 = disabled, 0 =
enabled)

Add ability to switch between MS and Intensity Stereo encoding modes -
The datasheet implies that turning off MS, turns on IS. IS is a good
way to lower the average bitrate, at the potential cost of additional
mpeg artifacts. This seems to be controlled by bit 5 of MAS register
address D0:7F0 (0 = IS, 1 = MS Stereo)

Is timecode insertion enabled or disabled? -
I think this timecode is worthless for most. Timecode is controlled
by bit 12 of MAS register address D0:7F1 (0 = disabled, 1 = enabled)

BTW, the Bit Reservoir setting (the "independent frames" setting in
the menus) isn't held through a power cycle. It always reverts back
to disabled ("Yes" in the menu.) Disabling the bit reservoir helps
editing, but wastes bitrate! Hopefully, this is just a bug in
Rockbox.

Also, isn't the built-in mic mono? In this case, selecting mic as the
audio source, should always enable mono recording, regardless of the
user setting. Why lower the quality with stereo encoding?!

Oh, one other thing. I think I remember this being reported already,
but I thought I mention it again, just to be complete.-- I notice
that if you set the mic gain all the way down to 21.1 dB, you get no
sound!

Ok, that is for the recording features. I also noted lots of playback
features missing/limited so far.:

Increase setting precision of Bass/Treble/Loudness controls -
I hate digital controls that have their precision artificially
limited, and the current 1dB steps are a bit too large anyway. The
datasheet says that about 1/8 dB (.125 dB) steps can be done for Bass
and Treble, and 1/4 dB (.25 dB) for Loudness. Bit [15:8] of the MAS
register addresses 00 14, 00 15, and 00 1E, respectively, control
these functions.

Add both "normal" and "super bass" loudness modes -
Currently, we can only disable (0 dB setting in the menu) and set the
level of loudness. However, loudness has two modes of operation, and
we currently can't select which one we want. I would suggest adding
setting another for "loudness mode" which would be "normal/super
bass." Bit [7:0] of the MAS register address 00 1E controls this
function (00 = Normal 04 = Super Bass)

Expand balance control to full dB range -
Could we have the balance controls expanded out to the full +/-127 dB
range that the MAS can do (1 db steps)? How about calibrating to
dB's, and not meaningless percentage values? This would be more
consistent with most of the other sound controls, that at calibrated
to dB already. Bit [15:8] of the MAS register address 00 15 controls
this function

Add optional mode for volume control calibrated to proper dB -
I'd much prefer the volume control calibrated to the correct dB scale
(-114 to +2 dB, or at least -116 to 0 dB) that the MAS shows in its
datasheet. For the status line volume display, just drop the minus
symbol, and it will fit in the same three character space used by the
current 0-100 scale.

Add the 20ms setting to Automatic Volume Correction control -
The datasheet says it has a 20ms setting, but it's missing in the menu
options. Bit [11:08] of the MAS register address 00 12 controls this
function.

And last, but *certainly* not least...

Add full user control of Dynamic Bass controls! -
Currently, we can only adjust Strength, leaving the settings for
Harmonics, Center Frequency, or Shape out of our ability to change.
It would be nice to be able to "tune" Dynamic Base to fit our own
particular headphones. The datasheet describes how to go about doing
just that. But, we need the controls there first! Also, currently
Strength is only adjustable in very coarse 10% increments. The MAS
allows much finer 1dB increments.

-- 
BRENT - The Usenet typo king. :)

Fast Times At Ridgemont High Info http://www.FastTimesAtRidgemontHigh.org Voted #87 - American Film Institute's Top 100 Funniest American Films



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