[mythtv-users] Razzy/Tinny audio

Fri May 9 16:41:47 UTC 2014

On Fri, May 9, 2014 at 11:47 AM, Stephen Worthington
<stephen_agent at jsw.gen.nz> wrote:
> On Fri, 9 May 2014 10:48:08 -0400, you wrote:
>
>>On Fri, May 9, 2014 at 3:29 AM, Stephen Worthington
>><stephen_agent at jsw.gen.nz> wrote:
>>> On Thu, 8 May 2014 23:59:10 -0400, you wrote:
>>>
>>>>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
>>>
>>> Create the ivtv_audio_fix.sh file (I have mine in /usr/local/bin where
>>> my change-channel-skynz.sh script is).  Then if your existing channel
>>> change script works at all like mine, you can just add these two lines
>>> at the end of it:
>>>
>>> # Workaround for bug which causes audio distortion on some recordings.
>>> /usr/local/bin/ivtv_audio_fix.sh /dev/videoPVR150 &
>>>
>>> What that does is to run the ivtv_audio_fix.sh script as a separate
>>> independent job (that is what & does).  The channel change script can
>>> finish and that lets MythTV know that the channel change has been
>>> done.  The ivtv_audio_fix.sh script will do its sleep while MythTV
>>> records for the sleep time (you will hear the tinny sound for the
>>> first few seconds of the recording, if it happened for that
>>> recording), then the script will wake up and do its fix.  The fix has
>>> to be done after all the recording startup work that MythTV does - if
>>> it is done too early it does not work as the v4l commands sent by
>>> MythTV override it.  When the ivtv_audio_fix.sh script has done its
>>> v4l commands it will just stop without reporting back to the script
>>> that called it (which finished several seconds before).
>
>>Hopefully I'm not over-reading this, what I did is create the
>>ivtv_audio_fix.sh file in /usr/local/bin, and I changed (near the top)
>>"device=/dev/video0" to "devive=/dev/videopvr150" and then added the
>>two lines to the end of my "change-channel.sh" exactly as yours is
>>(without the /dev/videoPVR150) [my uDev rule uses lower case pvr, my
>>bad] . This preceding issue is at the heart of my original question;
>>am I correct or wrong in assuming that the new name created by my uDev
>>rule should be reflected in the "ivtv_audio_fix.sh" script?  Thanks
>>again  Daryl
>
> If you exactly copied the two lines I posted to the bottom of your
> change-channel.sh, then it will not work, due to the mis-spelling of
> /dev/videopvr150 as /dev/videoPVR150 in what I wrote.  My
> ivtv_audio_fix.sh script accepts one optional parameter on its command
> line, the name of the device to control.  If that parameter is absent,
> it will use the default device setting you changed at the top of
> ivtv_audio_fix.sh.  It was not necessary to change that as the two
> lines I posted had the device name as a parameter.  So you either need
> to fix the spelling of /dev/videopvr150 on the call to
> ivtv_audio_fix.sh in change-channel.sh, or remove the /dev/videoPVR150
> from there and let ivtv_audio_fix.sh use its default device name that
> you have already fixed.
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What I exactly copied into my change-channel.sh was the last two lines
of your change_channel_skynz.sh, so I think I'm good with the audio
fix script edited to reflect the uDev name of my analog card and my
channel script calling the fix script just like yours does, not the
way you suggested had I not edited.

The University of Toronto is offering free online computer science
courses this fall, after applying myself in this direction I hope to
get a much better practical understanding of all the things that I've
received excellent coaching on from this list. Thanks Stephen, thanks
list, enormous thanks Devs, I love Mythtv.   (BE & FE)   Daryl