[LAU] Tutorial on sidechain compression in Qtractor and a question about screencasting

Philipp Überbacher hollunder at lavabit.com
Wed Aug 25 14:06:31 UTC 2010

Excerpts from Jeremy Jongepier's message of 2010-08-25 10:30:05 +0200:
> On 08/24/2010 04:48 PM, Philipp Überbacher wrote:
> > 
> > Ok, but on a much smaller screen it's hard to read/see things. It's hard
> > for me to see connections or which settings you used for the compressor.
> > 
> I agree, and I will post the settings of the compressor in the
> description of the video. Concerning the JACK connections, I'm aware
> that those can become illegible at lower resolutions. But then one can
> ask the question, is that the uploader's fault or a limitation of YouTube?

The question is what kind of display you assume those watching your
video have. It also depends on what you're showing. In a movie details
might not matter as much as in a tutorial.

> >> And the SC3 ports, I explain it in the video, the first two inputs of 
> >> the 3-channel Synth Duck track are for the stereo audio input you'd like 
> >> to compress and the third input is for the sidechain compression source, 
> >> in this case a kick from Hydrogen.
> >> For the outputs, 1 and 3 are the 
> >> compressed audio signals that I feed into the Synth Mix track.
> > 
> > Thanks Jeremy,
> > I managed to reproduce it with jack-rack, h2 and aeolus.
> > Yes, it's perverse to sidechain duck an organ, but I figured it would
> > provide a nice, constant sound, and thus be ideal for testing.
> > 
> > I had to enable 'create per-instrument outputs' in h2 to get the kicks
> > alone.
> > 
> Oh yeah, thanks for mentioning, I'll add that to the description too
> because you need per-instrument outputs in Hydrogen.
> > The routing in jack-rack is a bit funky.
> > in_1 is the sidechain input, in_2 the left and jack_rack_5655:sc3_1-1_i1
> > the right input.
> > So you hook up the h2 kick to in_1 and the signal to be ducked to the
> > next two ins.
> > You'll get the ducked signal left part from out_1 and right from out_2,
> > as you would expect.
> > 
> > The funky part is when the plugin is disabled though, in which case it
> > will route in_1 straight to out_1 and in_2 to out_2. If you go from
> > jack-rack straight to you speakers it results in the kick in the left
> > and the left signal in the right speaker.
> > 
> That part confuses me too, the internal routing of the plugin.

I wrote to Steve Harris about it yesterday and in the meanwhile figured
out how to change the port order in the sc3 ladspa plugin. It was rather
trivial, no C knowledge required.

As far as I can see, sc2 and sc3 in both ladspa and lv2 variants are
affected. Are there any more swh plugins with that kind of problem?

Writing patches for those would only take minutes, but the question is
whether it should be done. It would require re-routing in projects that
use the affected plugins. A lot of hosts don't support plugins where the
number of in/out ports doesn't match or isn't 1/1 2/2, so I think there
aren't that many projects affected.

> > Another thing worth mentioning with sc3 is that the 'chain balance'
> > parameter is most significant, you need to turn it up to hear any
> > ducking effect.
> > 
> That's right, it has to be set to 1 otherwise it doesn't use the
> sidechain signal:
> http://plugin.org.uk/ladspa-swh/docs/ladspa-swh.html#id1427
> > Thanks Jeremy, I wouldn't have bothered investigating without your video
> > :)
> >
> You're welcome. I like doing this stuff so hopefully more to come.
> > 
> >> I don't know where recordMyDesktop stores its raw/cache files, but afaik 
> >> I have encode on the fly disabled.
> >>
> >> Jeremy
> > 
> > It should be possible to figure out where it stores the raw data. I don't
> > know how to convert it to whatever yt prefers.
> > 
> recordMyDesktop stores its cache stuff in /tmp. Unfortunately the .tmp
> it creates can't be read by any app I've tried (ffmpeg, mplayer etc.).
> So I'm going to try ffmpeg with jack_capture.
> Best,
> Jeremy

"Wir stehen selbst enttäuscht und sehn betroffen / Den Vorhang zu
und alle Fragen offen." Bertolt Brecht, Der gute Mensch von Sezuan

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