Mailing List Archive: newbie audio problems

newbie audio problems

Jun 15, 2003, 3:02 PM

Post #1 of 5 (1215 views)

I'm relatively new to mythtv, I have things sort of working but am
having trouble with audio quality.

I'm running 0.9.1 on Debian with a 2.4.20 kernel and alsa 0.9.4. I have
a Gigabyte 7VAXP which has VIA 8235 sound built in. My capture card is
a WinTV GO.

With some screwing around I have managed to get btaudio to work with
analog output on /dev/dsp2. I am able to watch live tv and record. Sound
quality is however pretty poor no matter what I try. There is a fair
bit of hissing and crackling all the time.

If I run xawtv and do the "sox -r 480000 -c 1 -t ossdsp /dev/dsp2 -t
ossdsp /dev/dsp" thing then sound quality is vastly better. My question
is, how do I set the sample rate that high in MythTV for both live
watching and recording? I tried actually setting the samplerate to
480000 in the codecparams table manually but that caused backend
crashes. If I run sox all the time, then I am getting sound output all
the time which also isn't good.

I've searched through the mailing list which did help me get btaudio
going, but I couldn't find any solutions to the poor quality sound.

Can anyone help me out with this?

thanks

-Steve

Re: newbie audio problems [ In reply to ]

ijr at po

Jun 15, 2003, 5:08 PM

Post #2 of 5 (1181 views)

Permalink

On Sunday 15 June 2003 06:02 pm, Stephen Mathezer wrote:
> I'm relatively new to mythtv, I have things sort of working but am
> having trouble with audio quality.
>
> I'm running 0.9.1 on Debian with a 2.4.20 kernel and alsa 0.9.4. I have
> a Gigabyte 7VAXP which has VIA 8235 sound built in. My capture card is
> a WinTV GO.
>
> With some screwing around I have managed to get btaudio to work with
> analog output on /dev/dsp2. I am able to watch live tv and record. Sound
> quality is however pretty poor no matter what I try. There is a fair
> bit of hissing and crackling all the time.
>
> If I run xawtv and do the "sox -r 480000 -c 1 -t ossdsp /dev/dsp2 -t
> ossdsp /dev/dsp" thing then sound quality is vastly better. My question
> is, how do I set the sample rate that high in MythTV for both live
> watching and recording? I tried actually setting the samplerate to
> 480000 in the codecparams table manually but that caused backend
> crashes. If I run sox all the time, then I am getting sound output all
> the time which also isn't good.
>
> I've searched through the mailing list which did help me get btaudio
> going, but I couldn't find any solutions to the poor quality sound.
>
> Can anyone help me out with this?

lame can't encode with a sampling rate that absurdly high, and I doubt the a/v
sync code in mythtv deals with it either. Only way you're going to get it
working is to add some audio resampling code to the record pipeline to bump
the sample rate down to normal levels.

Isaac

Re: newbie audio problems [ In reply to ]

craigl at begeek

Jun 15, 2003, 7:42 PM

Post #3 of 5 (1189 views)

Permalink

Stephen Mathezer wrote:

>I'm relatively new to mythtv, I have things sort of working but am
>having trouble with audio quality.
>
>I'm running 0.9.1 on Debian with a 2.4.20 kernel and alsa 0.9.4. I have
>a Gigabyte 7VAXP which has VIA 8235 sound built in. My capture card is
>a WinTV GO.
>
>With some screwing around I have managed to get btaudio to work with
>analog output on /dev/dsp2. I am able to watch live tv and record. Sound
>quality is however pretty poor no matter what I try. There is a fair
>bit of hissing and crackling all the time.
>
>If I run xawtv and do the "sox -r 480000 -c 1 -t ossdsp /dev/dsp2 -t
>ossdsp /dev/dsp" thing then sound quality is vastly better. My question
>is, how do I set the sample rate that high in MythTV for both live
>watching and recording? I tried actually setting the samplerate to
>480000 in the codecparams table manually but that caused backend
>crashes. If I run sox all the time, then I am getting sound output all
>the time which also isn't good.
>
do you mean 48 000 here? as opposed to 480 000 like you wrote.

>I've searched through the mailing list which did help me get btaudio
>going, but I couldn't find any solutions to the poor quality sound.
>
>Can anyone help me out with this?
>
i've heard that with btaudio you need to set 32K as the sample rate. i
understood that this was all btaudio could handle, but it sounds like
you get it to work with higher raters, so maybe its something other than
btaudio that prevents >32K.

cheers,

CraigL->Thx();

Re: newbie audio problems [ In reply to ]

jcaputo1 at comcast

Jun 15, 2003, 8:20 PM

Post #4 of 5 (1202 views)

Permalink

> i've heard that with btaudio you need to set 32K as the sample rate. i
> understood that this was all btaudio could handle, but it sounds like
> you get it to work with higher raters, so maybe its something other than
> btaudio that prevents >32K.

It's not btaudio that needs 32000Hz, it's the card itself. Some (most? all?)
of the Haupauge WinTV cards are only capable of sampling at that rate. If
you request a different rate, I imagine different programs/drivers handle it
differently... they may try to up/down sample the audio, but this is where
the crappy audio happens. Try 32KHz in Myth, I think you might be pleasantly
surprised!

-JAC

Re: newbie audio problems [ In reply to ]

mathezer at yahoo

Jun 15, 2003, 8:34 PM

Post #5 of 5 (1215 views)

Permalink

* Craig Longman <craigl@begeek.com> [030615 21:03]:
> Stephen Mathezer wrote:
>
> >I'm relatively new to mythtv, I have things sort of working but am
> >having trouble with audio quality.
> >
> >I'm running 0.9.1 on Debian with a 2.4.20 kernel and alsa 0.9.4. I have
> >a Gigabyte 7VAXP which has VIA 8235 sound built in. My capture card is
> >a WinTV GO.
> >
> >With some screwing around I have managed to get btaudio to work with
> >analog output on /dev/dsp2. I am able to watch live tv and record. Sound
> >quality is however pretty poor no matter what I try. There is a fair
> >bit of hissing and crackling all the time.
> >
> >If I run xawtv and do the "sox -r 480000 -c 1 -t ossdsp /dev/dsp2 -t
> >ossdsp /dev/dsp" thing then sound quality is vastly better. My question
> >is, how do I set the sample rate that high in MythTV for both live
> >watching and recording? I tried actually setting the samplerate to
> >480000 in the codecparams table manually but that caused backend
> >crashes. If I run sox all the time, then I am getting sound output all
> >the time which also isn't good.
> >
> do you mean 48 000 here? as opposed to 480 000 like you wrote.
>

Nope, I do mean 480000. I got that from
http://lloyd.dyndns.org/index.php?MythTV%20Page by following the links
to the btaudio stuff:

http://lloyd.dyndns.org/index.php?Btaudio%20installation

It may be that I am SOL with this particular capture card and btaudio
unless I use sox to resample. For what it is worth, sox actually tells
me that the rate it ends up using is 192000.

> >I've searched through the mailing list which did help me get btaudio
> >going, but I couldn't find any solutions to the poor quality sound.
> >
> >Can anyone help me out with this?
> >
> i've heard that with btaudio you need to set 32K as the sample rate. i
> understood that this was all btaudio could handle, but it sounds like
> you get it to work with higher raters, so maybe its something other than
> btaudio that prevents >32K.
>
> cheers,
>
> CraigL->Thx();
>

I have no idea on that one. I have found btaudio rather difficult to
figure out.

So, I guess my choices are
-use sox to resample, I will play with this.
-record using the little loopback cable from my WinTV going to line in
(what to I set the record device to for this? /dev/dsp0?)
-get another card. If it costs a little bit more money to make this
work, then so be it. What does everyone else use? All I need is a
capture card, I have a separte video card with TV out.

thanks for any suggestions

-Steve