Anyone using FR as a phone? / Audio Codec meddling info

Andy Green andy at
Mon Jul 21 11:37:28 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:
| On Monday 21 July 2008, Cédric Berger wrote:
|> Sound quality during calls is indeed not that good.
|> 1. Volume is usually too low, but I think it can be modified via
|> correct settings.
|> Seems like people not always hear me at the same level : sometimes
|> quite ok, often really too low.  I have yet to try more...
| Volume can be adjusted vi a alsamixer, and the mic can be routed via a
| compressor and noise gate. Audio routing is far from simple - see the
| The route indicated for voice calls on the wiki is via the compressor
/ noise
| gate (ALC) but the state file (2007.2 after opkg upgrade) skips that
| Assuming there is sufficient difference in level between voice level
and the
| level from the earpiece it should be possible to set the noise gate so
| it only triggers when you are actually speaking, stopping the echo. The
| compressor should even out the variations in level.
| I don't know yet whether the assumption is true; it maybe that the ALC is
| skipped from the state file because it was difficult or impossible to
| settings that reliably blocked echo, but passed voice.

I don't know why we go around it, but when I looked mic -> GSM routing
some weeks ago I also found a very direct analogue path.  If you're
interested to meddle with this, I have some meddling hints.  First, the
datasheet is open:

We have fitted 100n in the external ALC path (between ACOP / ACIN)
instead of 1uF recommended, I guess it will impact low end, but in
telephony the low end as well as the high end are chopped out anyway.
Soon, as steve told, you'll be able to see this stuff (and our mistakes)
on the schematics for yourself.

You can dump the actual codec registers using

# cat /sys/devices/platform/soc-audio/codec_reg

and you can meddle with them like this

# echo "3d 20" > /sys/devices/platform/soc-audio/codec_reg_write

first one is the register address in hex, second is value to write in
hex.  I don't really know what those dozens of alsamixer settings are
doing either, I found it easier to read the datasheet and interpret /
meddle with the codec registers directly.

- -Andy
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