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Subject: Re: Unlocking the full features of the MAS chip (long, sorry)
From: Linus Nielsen Feltzing (linus_at_haxx.se)
Date: 2003-04-29


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
> options.

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
> Rockbox.

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
> sound!

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
place?

> 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

Oh really?

> 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.

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.

Linus



Page was last modified "Jan 10 2012" The Rockbox Crew
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