[mythtv-users] Razzy/Tinny audio

Daryl McDonald darylangela at gmail.com
Fri May 9 03:59:10 UTC 2014


On Thu, May 8, 2014 at 9:45 PM, Stephen Worthington
<stephen_agent at jsw.gen.nz> wrote:
> On Thu, 8 May 2014 12:44:23 -0400, you wrote:
>
>>Greetings Mythizens, as the subject implies I'm looking into
>>distortion from recordings on my analog card.
>>"http://www.mythtv.org/wiki/Hauppauge_PVR-150" this wiki suggests
>>adding a line to my change-channel.sh, like so: "sleep 5; v4l2-ctl
>>--set-audio-input 1 -d /dev/video0 > /dev/null 2>&1" . Before
>>implementing this solution, I'd like to confirm that since my UDEV
>>rule names the card "/dev/videoPVR150" then the added line of script
>>should reflect this change thusly?  "sleep 5; v4l2-ctl
>>--set-audio-input 1 -d /dev/videoPVR150 > /dev/null 2>&1" . Should
>>anything else be changed? The digital cards sound good and the analog
>>card has sounded good before, which is why I'm going for this idea
>>first.   TIA, Daryl
>
> This problem seems to be caused by mixing of audio from other sources
> on the card.  I have this problem with my PVR-500 (dual PVR-150).  It
> happens randomly at the start of using the card for a recording, and I
> have never been sure what the cause was, but the drivers have never
> been patched to fix it.  The fix you found does work, but what you
> need to do depends on what you are using your PVR-150 for.  If you are
> using it to tune to an analogue TV channel, then that fix is the right
> one.  If, like me, you are using its S-Video or composite video inputs
> to interface to an STB, then the fix is more complex.  In the latter
> case, you also need a command (v4l2-ctl -f <freq>) to tune the TV
> receiver to a frequency that is currently not in use by a signal it
> can receive.  This is to ensure that the TV audio does not get mixed
> into the S-Video connection's audio.
>
> This is what I have in my ivtv_audio_fix.sh file that I run from my
> channel change script:
>
> #!/bin/sh
>
> # Workaround for bug which causes audio distortion on some recordings.
> # From http://urlgrey.net/?p=231
>
> sleep 3
>
> if [ $# -eq 0 ]; then
>     device=/dev/video0
> else
>     device=$1
> fi
>
> # First, set the audio input in turn to each of the unwanted audio
> inputs.
> # This only became necessary as of Mythbuntu 12.04.
> v4l2-ctl -d$device --set-audio-input=2
> v4l2-ctl -d$device --set-audio-input=0
>
> # Next, also set the tuner frequency.  This also seems to be necessary
> # since Mythbuntu 12.04 to suppress a slightly different audio
> distortion.
> # The frequency should be for an unused part of the spectrum, as the
> unwanted
> # audio is coming from whatever the TV tuner is tuned to.
> v4l2-ctl -d$device -f 420
>
> # Reset the audio input to source 1 (the wanted input).
> v4l2-ctl -d$device --set-audio-input=1
>
>
> And this is my channel change script (change-channel-skynz.sh):
>
> #!/bin/sh
>
> REMOTE_NAME=Pace_RC-30
> cmd="$1"
>
> # If things work OK with sleep 1, try this for faster channel changes:
> # sleep 0.3
> sleep_amt=1.0
>
> # See if this helps with missing digits at the start of a channel
> change.
> sleep 1.0
>
> #echo Change channel: $cmd >>/tmp/irsend.txt
>
> case $cmd in
>     [0-9]*)
>     # make sure we unmute by hitting vol up
>     #/usr/bin/irsend SEND_ONCE $REMOTE_NAME Vol+
>     #sleep $sleep_amt
>     for digit in $(echo $1 | sed -e 's/./& /g'); do
>             #echo irsend SEND_ONCE $REMOTE_NAME $digit
>>>/tmp/irsend.txt
>         /usr/bin/irsend SEND_ONCE $REMOTE_NAME $digit
>         sleep $sleep_amt
>     done
>     ;;
>
>     *)
>         /usr/bin/irsend SEND_ONCE $REMOTE_NAME $cmd
>         ;;
> esac
>
>
> # Workaround for bug which causes audio distortion on some recordings.
> /usr/local/bin/ivtv_audio_fix.sh &
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Thanks Stephen, I use my PVR 150 to record from an analog STB
connected via RCA jacks, this card has apparently has five possible
input connections, one "tuner" via coax and two each of "component"
and "S-video". To leave my system connected as is, I would need to
create a new " ivtv_audio_fix.sh" file like yours, but change the name
of the tuner card appropriately and modify my "change-channel.sh" as
outlined in the original post? Or, maybe more simply, change the input
connection to "tuner" over coax and add the one line to my
"change-channel.sh"? with the first solution, I must need one more
line in the "change-channel.sh" to call the new "ivtv_audio_fix.sh"
script, right? But I'm not sure where to put it.
Daryl


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