[Bug 1267] New: Strong echo when calling a Neo from another phone

[bugzilla-daemon at bugzilla.openmoko.org]

http://bugzilla.openmoko.org/cgi-bin/bugzilla/show_bug.cgi?id=1267

           Summary: Strong echo when calling a Neo from another phone
           Product: Neo1973 Hardware
           Version: unspecified
          Platform: Neo1973
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Audio
        AssignedTo: sean_chiang at openmoko.org
        ReportedBy: mail at mmontour.net
                CC: buglog at lists.openmoko.org


This is a "well-known" issue but I couldn't find anything in Bugzilla for it.

When talking to a Neo, the person on the other end of the phone call will hear a
strong time-delayed echo of their voice. With the default settings it is bad
enough that it is difficult to hold a conversation, and it is even enough to
confuse IVR systems that use voice-recognition instead of DTMF tones.

It is possible to reduce (but not eliminate) the echo using the mixer, by
turning down the gain in the audio path from the microphone to the Calypso
input. However this also has the undesirable side-effect of reducing the volume
of the person who is speaking into the Neo. I am filing this under "hardware"
because I do not know if it will be possible to get acceptable performance using
only the mixer settings.

I have experienced this with a GTA01Bv4 and "-moko1" GSM firmware (one of the
first batch sold last summer), but it appears that this issue also affects GTA02. 

References:
http://lists.openmoko.org/pipermail/openmoko-kernel/2008-March/001477.html
http://lists.openmoko.org/pipermail/community/2008-January/012379.html

Note - a handy trick is to install 'xoscope' (which is in OE), a software
oscilloscope that measures the signal on the ADCs in the Wolfson codec. With a
few mixer tweaks it is possible to send a 1 kHz PCM tone out through the call
speaker, and measure the resulting microphone signal through the ADCs. It would
be even better to use a spectrum-analyzer program, but so far I have not been
able to compile one for the Neo.



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