Re: [ecasound] Seeing compression amount of LADSPA compressor?

From: Kai Vehmanen <kvehmanen@email-addr-hidden>
Date: Mon Mar 28 2005 - 16:24:45 EEST


I guess you've already got quite a few replies on linux-audio-user to
this topic, but just a few comments more from Ecasound POV...

On Sat, 26 Mar 2005, Iain Duncan wrote:

> Hi, I am planning on using ecasound to host midi and api controlled LADSPA
> plugins for live mastering, specifically compression and eq. I'd like to be
> able to assign midi controls or have other apps control the parameters, so
> ecasound seems like the right host. But on the other hand, being able to see
> the audio levels going in and the gain reduction amount is pretty helpful for
> setting them right. Is there some way to do this with ecasound? Does

The LADSPA compressors do not export any "current level" output
parameters, so you cannot monitor those, but you can monitor the audio

Try the following:

sh> ecasound -i foo.mp3 -o rtnull -evp -c
ecasound> start

... then issue "cop-status" to see the current peak volume for each
channel (nominal range [0.0,1.0]). After each "cop-status" (or short-hand
"es"), the peak value is resetted. You can add multiple -evp's:

sh> ecasound -i foo.mp3 -o rtnull -evp -el:sc4,3,3,3,3,3,3 -c

... to use the SC4 LADSPA compressor (used in JAMin) and monitor audio
before and after the compressor. I've not used SC4 this way, so I cannot
give tips concerning its parameters. You can do the same with Ecasound's
own compressor:

sh> ecasound -i foo.mp3 -o rtnull -evp -eca:69,0.01,0.5,1.0 -c

The same compressor is also available as a LADSPA plugin ("Dyson

Ecasound also provides "-ev", which gives more statistics about the signal
amplitude. You can use it in the same way as "-evp".

In addition to the interactive mode, you can write scripts or small
utils to adapt the tools to your purpose. For example ecasignalview is
built on top of the "-ev" operator. Try:

ecasignalview foo.mp3 rtnull

... that monitors audio levels of foo.mp3 while it is played on a dummy
sound device (rtnull).

Btw, replace "rtnull" with "alsa", "jack_alsa" or "/dev/dsp" if you want
to route the audio to a real sound device in the examples.

> ecamegapedal do this? And, if I use ecamegapedal for the gui, is it still
> possible to easily assign midi controls or use the api to control parameters?

With ecamegapedal, you cannot use MIDI controls, unfortunately.

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Received on Mon Mar 28 20:15:05 2005

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