[mythtv-users] Audio squealing and hissing

Christopher McCurdy christopher.mccurdy at gmail.com
Sat Mar 17 12:48:13 UTC 2007


On Friday 16 March 2007 9:08:28 am William Munson wrote:
> Christopher McCurdy wrote:
> > My mythtv backend has a WinTV-Go for recording. Up until a month ago,
> > I was using RCA video output from my directv receiver plugged into the
> > composite input, and the RCA outputs from the satellite receiver
> > combined into a stereo plug and plugged into the line-in slot on the
> > card. Sound was fine, a little tinny, but it worked well enough. From
> > there, I daisy-chained the line-out of the WinTV card to the line-in
> > on my motherboard (snd_cmipci). Everything was good.
> >
> > But now I'm using the coax cable as the input. The sound works, but it
> > produces a horrible squeal louder than the program's audio, and
> > sometimes it just distorts things. I've heard some things come out
> > octaves lower than they should be, but sometimes there is just buzzing
> > and cracking... always louder than the program's audio.
>
> I am not an expert on this but from what I understand, If you use the
> coax input then you are using the audio decoder built into the capture
> card. This audio is generally carried over the pci bus. You also have a
> jumper between the WinTV and the sound card which duplicates the audio
> path and creates the echo. Try removing that cable, you may find it
> still works.

I've tried to remove the cable patching line-out (WinTV) to line-in 
(soundcard), but then I get no sound at all. I tried to change the audio 
recording input to /dev/dsp1, since the snd_bt87x gets autoloaded, but that 
also produces no sound. Logs show this whenever I try to use the /dev/dsp1 
input: 

NVR: Only read -1 bytes of 4096 bytes from '/dev/dsp1
read audio: Input/output error

This is what my lspci says, though, so it seems I have audio capture. Although 
should I open up my case and make sure I have the MSP34xx chip on the board?

02:06.0 Multimedia video controller: Brooktree Corporation Bt878 Video Capture 
(rev 11)
        Subsystem: Hauppauge computer works Inc. WinTV Series
        Flags: bus master, medium devsel, latency 32, IRQ 17
        Memory at df000000 (32-bit, prefetchable) [size=4K]
        Capabilities: [44] Vital Product Data
        Capabilities: [4c] Power Management version 2

02:06.1 Multimedia controller: Brooktree Corporation Bt878 Audio Capture (rev 
11)
        Subsystem: Hauppauge computer works Inc. WinTV Series
        Flags: bus master, medium devsel, latency 32, IRQ 17
        Memory at de800000 (32-bit, prefetchable) [size=4K]
        Capabilities: [44] Vital Product Data
        Capabilities: [4c] Power Management version 2


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