[mythtv-users] Audio squealing and hissing

[William Munson]

Christopher McCurdy wrote:
> On Saturday 17 March 2007 1:07:29 pm William Munson wrote:
>   
>> 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.
>>
>>     
>
> I had assumed that since my sound card (CM8738) uses /dev/dsp, if I were to 
> remove the patch cable, I should be recording audio directly from the TV 
> card. Either way, I don't appear to have the MSP34xx chip that's needed for 
> audio recording on the card.
>
> bttv: driver version 0.9.16 loaded
> bttv: using 8 buffers with 2080k (520 pages) each for capture
> bttv: Bt8xx card found (0).
> bttv0: Bt878 (rev 17) at 0000:02:06.0, irq: 17, latency: 32, mmio: 0xdf000000
> bttv0: detected: Hauppauge WinTV [card=10], PCI subsystem ID is 0070:13eb
> bttv0: using: Hauppauge (bt878) [card=10,autodetected]
> bttv0: gpio: en=00000000, out=00000000 in=00ffffdb [init]
> bttv0: Hauppauge/Voodoo msp34xx: reset line init [5]
> bttv0: Hauppauge eeprom indicates model#44801
> bttv0: using tuner=8
> bttv0: i2c: checking for MSP34xx @ 0x80... not found
> bttv0: i2c: checking for TDA9875 @ 0xb0... not found
> bttv0: i2c: checking for TDA7432 @ 0x8a... not found
> bttv0: i2c: checking for TDA9887 @ 0x86... not found
> bttv0: registered device video0
> bttv0: registered device vbi0
> bttv0: PLL: 28636363 => 35468950 ..<5>sd 0:0:0:0: Attached scsi generic sg0 
> type 0
>   
Ok, then you will need your patch cable. You might try setting the 
line-in /line-out levels lower in case you are blowing away the audio 
card A/D converter. Not sure what else to check.