Re: sound recording
On 2007-03-05, BALLABIO GERARDO <GERARDO.BALLABIO@mpsgr.it> wrote:
> (please Cc: me, I'm not subscribed)
>
> Hi all,
>
> I'm trying to convert some old analog music recordings to CD format,
> using my PC running Sarge. I've found some directions in a howto, buyed
> a cable and plugged one side into the headphones output of my stereo,
> the other one into the line-in input of the PC. This worked fine: I can
> play my audio tapes on the stereo and hear them on the PC speakers. I
> can also record them with arecord, cut tracks with sox and burn CDs with
> cdrdao (I like command line tools).
>
> The problem showed up when I tried to do the same thing with a videotape
> (I just want to record the audio track, not the video). I plugged the
> cable into the headphones output of the TV, but this time something
> strange happens: the music plays fine on the PC speakers, but when I try
> to record it, the recorded track (wav file) is disturbed by a constant
> and annoying high-frequency whistle. I would think that arecord would
> record the exact same sound I hear on the speakers, but it doesn't and I
> have no idea why. Suspecting that some other signal was being recorded
> alongside the TV output, I opened the mixer (Gnome menu -> multimedia ->
> volume control) and muted all channels but Master, PCM and Line-in (I
> don't know what PCM is, but I found experimentally that if I mute that,
> the signal from line-in is muted too), but it didn't work, it was just
> the same as before. I'm really puzzled.
>
> Does anyone know what's happening and what should I do?
>
> Thank you in advance
> Gerardo
The horizontal frequency of the video is probably bleeding through
into the audio, and producing a beat tone with the sampling
frequency of the sound card while recording. You would not hear
it while listening to the signal, because it is routed from the
line input of the soundcard to the speaker out without being
digitised first. Run the vcr audio through a low-pass filter
before sending it to the input of the sound card.
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