Am Mi 29. Oktober 2008 schrieb Erland Lewin: > Here is some speculation on the GSM buzz issue: > > I was doing some testing today, calling my SIP number connected to my server > and recording the audio. > > Firstly, I have never been able to get a strong signal (high sample values) > at the receiving end when calling from the Freerunner, despite trying > various ALSA state files. > > Today I tried holding the Freerunner flat in front of my face (as opposed to > holding it with the earphone beside my ear. I got a significantly stronger > signal at the other end with the microphone orientation like this. Not only > did I get a stronger signal, but also a weaker background GSM buzz. My guess > is that this is because the ALC (Automatic Level Control) of the Wolfson > chip decreased the gain of the microphone amplifer whereby the GSM buzz also > decreased. > > Is the signal from the microphone in general is so low that the Wolfson chip > needs to run at max gain (and still doesn't manage to get a very strong > output signal)? And that this high gain makes the GSM buzz so loud (despite > being fairly low on the input)? > > Is there anything that could be done to increase the signal from the > microphone? It seems to me like this might improve audio quality, > transmitted audio level, and decrease GSM buzz. Is there a bias voltage that > can be increased? Could the mic be replaced with a more sensitive one? By > the way, is there a data sheet for the microphone? > > Comments? >
there is no ALC involved inside Wolfson, on standard GSM-handset.state profile. Your observations make perfect sense though, assuming the ALC is done on network side (or *inside* calypso chipset). Alas there's very obviously nothing we can do via mixer settings to improve this situation. cheers jOERG
signature.asc
Description: This is a digitally signed message part.
_______________________________________________ hardware mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/hardware
