[mythtv-users] Sound problem with BT878 capture card

Chad masterclc at gmail.com
Tue Aug 29 08:43:14 UTC 2006


On 8/29/06, Lachek Butalek <lachek at gmail.com> wrote:
> A question which, I'm sure, has been asked a million times before but
> which I could not find a solution to after hours of Googling. Please
> be gentle.
>
> I have an analog BT878 capture card, a V-Stream VS-TV878RF more
> commonly known as the KWorld BT878 tuner. It is card=78 in the BTTV
> driver, and I'm also using tuner=2 which seems to work fine.
>
> The card has an analog audio passthru port, into which I have plugged
> a stereo 1/8" audio patch cable that ends in my sound card (Ensoniq
> AudioPCI) Line port. Using this setup with xawtv - and the Line port
> *not* muted - works fine: I can hear the channel I'm currently tuned
> to in real time. Generally, audio playback (using mpg321, KDE system
> sounds etc) separate from MythTV works fine on my system as well.
>
> The issue is with recorded content, including "Live" TV - there is an
> audio stream in the files (my video analyzers all report there is a
> 128kbit MP3 stream present) but it is dead silent. While in MythTV,
> disabling mute on the Line port allows me to hear the channel (albeit
> delayed, because of the encoding overhead of Live TV) being tuned to,
> but the moment I enable mute as I'm supposed to I can no longer hear
> the audio.
>
> I've tried to mute the Line port, tune to a channel using xawtv and
> then 'aplay /dev/dsp' but that results in nothing but a few clicks and
> then nada - it reports a frequency of 8000bits (shouldn't that be
> 32000?) and mono (shouldn't that be stereo?), gives a few underrun
> errors like it's supposed to, and then stops.
>
> I've also tried to tinker with the settings in the Myth frontend, such
> as setting the audio device to ALSA:default and the Device to default
> - no apparent errors, but no sound either. Besides, since I have no
> audio content in my recorded files I presume the problem is with the
> backend rather than the frontend.
>
> When configuring a capture device using mythtv-setup, there is an
> option for audio device which is currently set to /dev/dsp. Is that
> correct? Should it be changed to something - esp since I'm trying to
> use all ALSA devices to narrow down the problem? Is there a more
> low-level way - ie not so MythTV specific - to test recording audio
> from an analog tuner?
>
> Any assistance greatly appreciated.
> _______________________________________________

In alsamixer, if you hit F4 it will take you to the capture options.
In there should be your answer.  Changing the capture device to the
Line-in (assuming that's how it's connected) and increasing the
capture volume will hopefully fix that up.  All of the rest of your
settings all sound pretty accurate, however it's been a while since I
used one of my bt87x based cards.

Good luck!

-Chad


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