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

Jeremy Jongepier jeremy at autostatic.com
Tue Aug 24 13:09:12 UTC 2010

On 08/24/2010 01:34 PM, Philipp Überbacher wrote:
> Excerpts from Jeremy Jongepier's message of 2010-08-24 10:22:57 +0200:
>> Hello all,
>> I've uploaded a new tutorial to YouTube:
>> http://www.youtube.com/watch?v=pnAqk054g7E
>> So using sidechain compression in Qtractor with the SC3 LADSPA plugin.
>> Concerning screencasting, anybody any experience with this? For this
>> tutorial I used recordMyDesktop, but it captures video to Theora, so
>> after editing and uploading the quality degrades considerably. The big
>> advantage of recordMyDesktop though is that it has JACK support and that
>> the overhead is pretty small so I can still run my setup at a decent
>> latency.
>> I've also started playing around with FFmpeg. The video quality is
>> waaaaay better if you capture to a lossless format but I'm having my
>> thoughts on the audio part. I compiled FFmpeg myself with libjack-dev so
>> it has JACK support. But FFmpeg apparently has troubles to keep up with
>> latencies below 20ms, lots of xruns on the FFmpeg side (JACK doesn't
>> complain though). And I have the feeling FFmpeg lags on the audio side.
>> So I'm thinking about capturing the video part with ffmpeg and the audio
>> part with jack_capture and mux the stuff later. But if anyone has any
>> other suggestions, let me know.
>> Best,
>> Jeremy
> Hi Jeremy.
> I know little about screencasting, but I do know that recordmydesktop
> can either encode on the fly or afterwards. Maybe it's possible to use
> and convert its raw data, whatever format that may be, to something else?
> The tutorial seems quite nice. I do have a little trouble with it
> because you seem to have a really high resolution screen, and my biggest
> screen has 1280x800. I'm also not sure it's a good thing that you can't
> see the mouse, recordmydesktop has an option for that.
> Seems to be quite a hassle to set sidechain compression up. The essence
> being: know which sc3 port corresponds to what and what to route where.
> I sadly couldn't get that from the video because of aforementioned
> problems.
> Regards,

Hello Philipp,

Concerning the mouse, that's a noob move.
I'm using a 1920x1080 resolution, which is also the maximum YouTube HD 
resolution and this should yield the best results: 
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.
I don't know where recordMyDesktop stores its raw/cache files, but afaik 
I have encode on the fly disabled.


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