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Rockbox mail archiveSubject: Unlocking the full features of the MAS chip (long, sorry)Unlocking the full features of the MAS chip (long, sorry)
From: Brent Geery <fasttimes_at_mochamail.com>
Date: Mon, 28 Apr 2003 13:09:27 -0700 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 FilmsReceived on 2003-04-28 Page template was last modified "Tue Sep 7 00:00:02 2021" The Rockbox Crew -- Privacy Policy |