[mythtv-users] Audio squealing and hissing

[William Munson]

Christopher McCurdy wrote:
> 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
>   
Two things I can think of. First one, unless you have 2 capture cards 
your device should be /dev/dsp or /dev/adsp. The second thing I would 
try is to open whatever audio mixer program you use (alsamixer) and make 
sure that the appropriate audio input is not muted. After a reboot take 
a look at dmesg and see what devices your WinTV card attaches to and use 
them in the capture card setup in mythtv-setup.