[vorbis] Realtime resampling/encoding with oggenc

[vorbis]

On Tue, 15 May 2001, Beni Cherniavsky wrote:

Yes it is a good idea to throw out everything above 16kHz.  FM doesn't
give you anything above that anyway and for my station here, I get a nasty
19kHz feedback spike or something that confuses vorbis.  Now
that I'm cutting it out, vorbis doesn't have to waste bits trying to
replicate that nasty high pitch spike.  I get better compression and
vorbis uses the bits where it counts as well.

As for AM, I'm not sure, but I'd probably throw out everything above
10kHz and below 100Hz.  If I'm not mistaken it doesn't go above or
below that. Maybe someone knows what AM is optimzed for exactly.

I only use vorbis to record live sources as well because for some reason,
if the channels are not centered, lame's joint stereo gets confused and
introduces artifacts without fail (could use true stereo... but hey, 
vorbis kicks its ass).  Every single time.  

Vorbis's true stereo optimizations do a better job on the channels
independently.  Recordings taken from the radio and listened to on a nice
setup (pioneer amp,  acoustic research speakers, soundblaster 64AWE) sound
indistiguishable from the original (actually better because that stupid
19kHz spike is gone).

As for having to kill sox... I don't have much experience with sox, but
from what I can tell, there is no way to exit gracefully.  Man page, web
search, deja.com search yield nothing in the way of stoping sox
gracefully.  The best way to do it seems to be as stated.

--james

> On Tue, 15 May 2001, vorbis wrote:
> 
> > Don't know if anybody is still missing the lame oggenc features for
> > resampling, lowpass/highpass filters etc, but I wrote a little script that
> > uses sox to do all the stuff I need to real-time encode oggenc from the
> > radio, or any input device.
> > 
> > #!/bin/bash
> > DATE=`date '+%m-%d-%Y-(%H.%M)'`
> > DESTIN=/video/music/perftoday
> > export DATE=$DATE'-PerformanceToday.ogg'
> >  
> > sox -V -r 44100 -c 2 -t ossdsp -w -s /dev/dsp -t wav - filter \
> > 0-16000 2>/dev/null | oggenc - -o $DESTIN/$DATE -b 128&
> > sleep 7200
> > kill -9 $!
> > 
> > What you see here on the first two lines should be only one.  Note the
> > "\".
> > 
> > As you can guess, I use this to record my favorite classical music program
> > on NPR.  Anyway, I hope this solves somebody's problem similar to mine.
> > 
> Is it always healthy to lowpass a signal from the radio at 16KHz?  Is it
> the same for AM and FM?  I record most of my Ogg files from the radio
> (usually through an intermediate tapa cassete - how does this effect?).  
> I usually encode without filtering.  I only once noticed that for a
> particular station which was recieved very weakly, there was a parasitic
> 18Khz noise.  Should I get into the habit of filtering?
> 
> Unrelated question: the above script seems to kill the encoding as the
> normal means for ending a recording - is this a safe thing?  Does it only
> produce a little bad page/packet at the end that one can live with?
> 
> 

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