Rockbox mail archiveSubject: Re: Unlocking the full features of the MAS chip (long, sorry)
Re: Unlocking the full features of the MAS chip (long, sorry)
From: Linus Nielsen Feltzing <linus_at_haxx.se>
Date: Tue, 29 Apr 2003 01:18:41 +0200
Brent Geery wrote:
> I'm not a programmer, but I can read a datasheet. :)
I am a programmer, and I have read the datasheets. Many times.
> After taking another look at the MAS datasheet, I've noted several
> features that have not yet been implemented as user configurable
Maybe I'm just old and cranky, but I don't take this kind of "why
haven't you done all this yet" comment all too well. My available time
for this project is limited. I have worked hard to get the recording
stable before adding detailed features. I have intended to add moe
control over the recordings, I just haven't come to that yet.
> Recording issues first.:
> Add ability to disable/enable CRC protection -
Please explain to me what you intend to gain by not using the CRC. Two
extra bytes for data? Sure, we can add a CRC option, I just didn't think
anyone would mind it being 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)
Sure. If you want lower quality, go ahead and file a request.
> 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)
Of course the timecode is disabled. Do you really want an option for that?
> 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
A bug indeed. This is fixed now.
> 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?!
Earlier in this letter you wanted more options, now you want less.
Explanation: It was easier writing the recording code when all options
were selectable regardless of source. But sure, mono is the best choice
for mic recordings.
> 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
Yes, that's the way the MAS works. Don't ask me why.
> Ok, that is for the recording features. I also noted lots of
> playback features missing/limited so far.:
Sure, sure, sure.
And other people complain that there are too many options/settings.
> 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.
If I add better precision for this, other people will complain about
them being too fine.
> Bit [15:8] of the MAS register addresses 00 14, 00 15, and 00 1E,
> respectively, control these functions.
I know this. How do you think I coded the existing settings in the first
> 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.
Maybe I haven't used that much audio equipment, but I haven't seen any
device so far with a balance control with dB as a unit. Do you feel that
the balance control is inadequate?
> Bit [15:8] of the MAS register address 00 15 controls this function
> Add the 20ms setting to Automatic Volume Correction control - The
> datasheet says it has a 20ms setting, but it's missing in the menu
Yes, we have left that option out, since it is useless for music
listening. We reset the volume for every track change anyway.
> 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.
This is planned.
Received on 2003-04-29