Buzzing on GSM audio

Andrew Bruno aeb at
Sat Jul 26 06:38:27 CEST 2008

> Dave Clark wrote:
>> Can you correlate the buzzing to your signal level?  IIRC, most phones
>> will increase transmit power as needed to overcome noise.  If the noise
>> is caused by RFI from the GSM radio, increased power would tend to
>> increase the interference.
> I have a very low signal here one bar at most, I haven't tried it where
> there is good reception, as
> I can't really use it as a phone yet. However with that clue I'll try it
> ASAP in an area where I get
> better reception.
> FWIW my other Cell phones also get very low reception here, but don't have
> any noise.
> I hope if this is a H/W problem we can get it fixed even after the
> warranty expires as it definitely
> makes the phone a brick otherwise.

I'm also experiencing buzzing during GSM calls. I'm running the latest
2007.2 and using a T-Mobile sim in US. From my testing the buzzing sound
is only heard on the other end (the person I'm calling). On the neo side
things seem fine.

FWIW, I've found tweaking these specific settings in
/usr/share/openmoko/scenarios/gsmhandset.state effect the intensity of the
buzzing sound. Specifically:

  * 'Mono Playback Volume'   (85)
  * 'Mono Sidetone Playback Volume'  (7)
  * 'Mic2 Capture Volume'     (3)

Finding a balance between these settings helped to somewhat alleviate but
not eliminate the buzzing sound. If these are set too low the person on
the other end doesn't hear the buzz or my voice, If set too high my voice
gets louder along with the buzzing.

I also found tweaking these two settings effect the volume of the caller
(on the neo side):

  * 'Speaker Playback Volume'  (112)
  * 'Bypass Playback Volume'    (7)

Setting these too high and the person hears their voice echo, too low and
you can't hear the other person on the neo side.

I played with alsamixer during several calls and can't seem to find the
right settings to completely remove the buzzing but it sounds like this
can't be completely fixed in alsa. The bug looks to be here[1]. I also
found this thread[2] searching through the archives which mentions it
could possibly be a hardware issue? Sounds like there was similar problems
with GTA01.

As previously mentioned, it would be interesting to see if others are
experiencing buzzing on other images/carriers etc. I plan on picking up
one of the working ATT sim cards to test with a different carrier and will
post any results.

If anyone has any other suggestions on possible tweaks I'm willing to help
test. I'd love to see this bug resolved as I'm hoping to start using my
FreeRunner as my main phone.



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