Re: echo (was: ASU software - pre-pre-release impressions)
On Tue, May 20, 2008 at 07:19:34PM -0700, Mike Montour wrote: In my tests the echo went away when I muted the Neo's speaker or microphone, so it did not seem to be a network issue. The audio coupling between the Neo's speaker and microphone can be measured independently of the GSM stuff, e.g. with the 'Jaaa' audio analyzer from http://www.kokkinizita.net/linuxaudio/ or with 'xoscope'. Various ALSA mixer controls will affect the level of the coupled signal, but these also affect the intended sound paths (loudness of the speaker and sensitivity of the microphone). The mixer settings have to be selected to give the best compromise between these factors. I once heard an interesting story about the human body: supposedly, the mouth is so close to the ear that if you'd talk aloud a lot, you'd damage your own hearing. The body hacks around this by putting some slight tension on the eardrum while speaking, effectively muting incoming sound a bit and preventing damage. I wonder if we could take advantage something like this to reduce echo, e.g. reducing mic gain when input is high or reducing volume when mic input is loud. But, let's not try and fix things before we're sure they're (still) broken :). Arnout ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: echo (was: ASU software - pre-pre-release impressions)
Crane, Matthew wrote: I've noticed that with GSM calls in general there is sometimes an echo. It can be very pronouced or barely noticable. It may be hw or sw, but it may not have anything to do with either caller's phone. If it doesn't happen consistently and is not reproducable, it's likely the network. IMHO. In some cases it might be from the network, if it was using a buggy or mis-calibrated echo-cancellation algorithm. However the Neo itself is also quite capable of generating an echo - some of the sound coming out of its speaker is picked up by its microphone, and is then encoded and sent back to the other caller. In my tests the echo went away when I muted the Neo's speaker or microphone, so it did not seem to be a network issue. The audio coupling between the Neo's speaker and microphone can be measured independently of the GSM stuff, e.g. with the 'Jaaa' audio analyzer from http://www.kokkinizita.net/linuxaudio/ or with 'xoscope'. Various ALSA mixer controls will affect the level of the coupled signal, but these also affect the intended sound paths (loudness of the speaker and sensitivity of the microphone). The mixer settings have to be selected to give the best compromise between these factors. I hope that the overall audio quality will be good enough once the mixer settings have been optimized, but I am not yet confident of this. Audio-quality reports from other Freerunner owners would be appreciated. ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
