[linux-audio-user] Information on using LADSPA plugins

Mike Rawes linux-audio-user@music.columbia.edu
Sun Oct 12 19:09:00 EDT 2003


On Sun, 12 Oct 2003 12:23:41 -0800
"Paul Berry" <pnberry@gustavus.ak.us> wrote:

> Greetings all:
> 
> I am trying to learn about the LADSPA plugins. I have downloaded and
> installed the ladspa_sdk, read the ladspa.h header file and read Dave
> Phillips article on the O'Reilly network. I've also added the CMT
> plugin library.
> 
> Okay, so I've got my plugins but I need some helping making them go. I
> don't really understand how they work. I am trying to learn about them
> in a console environment, that is to say just by themselves (if that
> is possible, maybe that is part of the difficulty). I understand the
> basics of the C language and the Linux operating system but most of
> the information I have found seems to cover developing plugins and
> consequently goes right over my head.

The plugins can't be used by themselves - they need a host application,
that provides connections to sound devices, allows you to set control
values etc. 
 
> Lets say I wanted to use the sine.so plugin from the sample library to
> play a continuos pitch from my sound card, how would I do that? I'm
> confused by the need of an input file for this as I see the sine.so
> plugin as the source. Can the output file be a dev file? How about
> using the ALSA hw plugin hw:0,0 as the output, how would I do that?
> I've read the ALSA library documentation about plugins and LADSPA but
> again it goes right over my head.

'applyplugin' which comes with the ladspa_sdk assumes you are processing
.wav files, applying a plugin as an effect. Most LADSPA hosts are GUI
driven, and the only commandline host I have found is ecasound (which
does a whole lot more!) - from the ecasound web page:

http://www.wakkanet.fi/~kaiv/ecasound/welcome.html

example to play a sinewave (under 'effects processing'):

ecasound -i null -o /dev/dsp -el:sine_fcac,440,1

(no input, output to /dev/dsp, use ladspa plugin sine_fcac with
frequency 440, amplitude 1)

Use analyseplugin from the ladspa_sdk to get details of the plugin label
and ports.

Ecasound also comes with a nice interactive cli, which allows you to
build 'chains' of plugins amongst other things. The manpages will tell
you all about it.

- 
Myk



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