Freerunner audio channels
dfokkema at ileos.nl
Fri Aug 7 15:29:26 CEST 2009
I finally took a lunch break to check out the various alsa channel
settings. Angus's mixer scripts rock, BTW! Trying to track down the
input for the handset, I've looked at the wolfson schematic, browsed
through the handset state file and can only come to the conclusion that
the audio path is completely circumventing the digital filter module.
Why is that? We're only using the sidetone path and mixing that as the
only channel into the output. The rest is disabled (volumes set to 0 and
switches set to False). Reading up on what sidetone actually is
(wikipedia) I get the feeling that we're not supposed to do this. Ok, it
works, but the sidetone path was never intended for this purpose, I
gather, but rather to provide feedback to the speaker's earpiece.
I tried to decipher the various wiki pages dealing with audio and the
conflicting posts on alsa settings and played with Angus's mixer during
a phone call (FR in my one hand, landline with covered up mouth piece in
my other) and noticed that setting Mic2 Capture Volume to 0 does _not_
mute the Mic. It _does_, however, enable me to set the Mono Sidetone
Playback Volume quite high (6 / 7) as well as the Mono Playback Volume
(100 / 127).
This post is not intended to start another discussion on 'best'
settings, but maybe some of you know the answer to these questions:
- Why exactly are FR's different while I've never heard of Nokia users
needing to tweak mixer settings.
- Why does setting Mic2 Capture Volume to 0 _not_ (almost) mute the mic?
- Why do we bypass the digital filters by using the sidetone path?
Maybe this information is buried somewhere but I can't unearth it.
PS: It seems that I can now use my FR to actually make phone calls, ;-)
PPS: If these questions are answered, maybe I'll stick my neck out and
delete all conflicting information on the wiki and write a small 'How to
set your mixer settings appropriately?'
PPPS: I'll not do anything rash, I promise. However, it would be nice to
reach some kind of consensus and clean up the wiki. It took me far too
much time to tweak my phone to make calls without noise, echo etc.
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