Howdy, all. I've been having a problem with audio on my
Asus Z70Va (a.k.a. M6Va, a.k.a Chembook 2370Va) which has
me pulling out what little hair I have left. Most of
the audio is working, but one aspect of it is not.
I'm running ALSA 1.0.13 on a 2.6.19 kernel. The ALSA
modules are being loaded without any specific options
(the codec modules doesn't appear to have a configuration
for this particular model). The codec is indicated to be
an ALC880.
Audio output works fine, both through the internal speakers
and to a headphone plugged into the case-side output jack.
The built-in microphone works. It seems to pick up quite a
bit of ambient noise (e.g. from the laptop fans) but that's
only to be expected, I suppose.
However, if I plug a standard line-level audio source into
the side-panel input jack (which has a microphone icon printed
by it), the input works very badly. The problem I see is an
interesting one. In both the audio mix (if I unmute and
turn up the "Line" mixer input) and in the capture input
(if I set the capture-1 input to "line" and enable it at
a reasonable level), I can get reasonable audio quality only
if the input level, and the internal mixer settings are cranked
far, far down.
If I try to turn up the mixer to the point where the input
signal ought to be getting an audio signal of more than a
few percent of full-scale, things go all to heck. I hear
a sharp static-like sound, which appears whenever the input
signal exceeds a low level. If I do an audio capture, I
see a reasonable-looking waveform at low levels, but if the
waveform attempts to increase very far at all from the zero
line it starts exhibiting sharp transients (they look a bit
like the noise that dust on an LP record creates).
This does not appear to be a simple matter of clipping... the
waveform is not flat-topped. Quite the opposite - it's as if
the waveform is spiking out of control when it tries to exceed
a given level.
The problem does not affect the built-in microphone... if I
whistle at it when capturing from it, the whistle signal rises
up cleanly above the background noise and does not exhibit any
sort of spiky noise.
The problem affects captures using both the native ALSA
interfaces, and via the OSS compatibility layer... and
as I said it also affects the input->mix->output path.
It does not appear to be an artifact of ALSA sample-
rate conversion - I've tried configuring ALSA to disable
SRC for the applications I'm using, and configuring those
applications to ask for the data at one of the codec's
native rates... and the problem persists.
I've tried experimenting with the codec module, loading it
with a "model=z71v" parameter as suggested by an article I
found via Google. This model specification greatly changes
the number of mixer controls and inputs presented by the
driver, but it appears to have no effect on the noise problem...
I still get noise from this input.
Any idea what I'm doing wrong? Am I mistaken in my belief
that this laptop model _should_ be capable of accepting a
line-level input through the input jack if its input is
properly configured? Do I need some other sort of model
specification to the codec driver (perhaps one not yet
actually supported) to configure this input correctly?
My current suspects are two:
[1] The codec driver is for some reason not configuring the
"line" channel correctly - wrong data format, perhaps -
and the incoming data is being misinterpreted whenever
the codec sends in data samples which don't fit properly
into an 8-bit value.
[2] My laptop's line input is physically broken, somehow,
and the signal is being corrupted in a strange way
before it's ever digitized by the codec.
Assistance or ideas would be greatly appreciated! I
want to use this laptop for some ham-radio applications
(PSK31 and etc.) and can't do so until I can get the
sound-card input to work correctly.
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