[linux-dvb] cx88-alsa audio quality?

Mauro Carvalho Chehab mchehab at infradead.org
Mon Sep 29 16:06:35 CEST 2008


On Mon, 29 Sep 2008 01:01:51 -0500
Vanessa Ezekowitz <vanessaezekowitz at gmail.com> wrote:

> I forget if I've already mentioned this yet...
> 
> I recently started playing around with analog NTSC television again on my system, while trying to help someone solve a problem on their system.  In the process I ran into a problem getting cx88-alsa to build with the rest of the v4l-dvb repository.  As it turned out, mine was one of the stock Ubuntu kernels that have some odd issue with the I2C configuration.   I had to build a vanilla kernel (2.6.26.5), making all the I2C stuff into modules as opposed to built-in.  So, that's fixed - cx88-alsa builds and loads OK now.
> 
> However, I have a new problem:
> 
> Something has broken the output that cx88-alsa creates.  In the case of my Kworld ATSC 120, radio output on all frequencies has a sort of growling "industrial" noise on top of the actual audio, kinda like the background noise of a manufacturing facility.
> 
> Analog TV on all channels gives clean but very tinny audio, as though the sample rate were really low (~8kHz).
> 
> Since other audio sources are working fine, I can't tell if this is a bug in the kernel, or cx88-alsa, or something else entirely.  I've only noticed the problem for a matter of a week or less, so I'm not sure when it started.  The problem persists as of today's pull of the v4l-dvb repository.
> 

This may be due to some issue at alsa libraries or at pulseaudio. On some tests
I did with alsa, depending on the way you specify a device, you may have
noise (I had lots of noise on my alsa microphone input, depending on the syntax
I used to specify its input entry). You may specify it as hw: or as plughw:. The
difference between them is the way libalsa will handle it, and what is
specified on your alsa config files.

Cheers,
Mauro



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