[CM] LADSPA implementation

[e deleflie]

There is LV2 (http://lv2plug.in/), apparently the 'successor' spec to
LADSPA but there isn't much evidence of uptake (in either form:
plugins or hosts).... perhaps still a bit early.

...  I still cant get apply-ladspa to write to the 'currently
selected' sound. I've written a simplified test script that
illustrates my problem (included below). So far, with my track-record,
I've probably written some bad code somewhere ... although the below
script executes without errors, but the resultant file is empty...

#!/usr/local/bin/snd -b
!#
(use-modules (ice-9 format))
; set some global variables
(set! (ladspa-dir) "/usr/lib/ladspa")


(let* ((outsound (new-sound "out.wav" :channels 2))
        (insound (open-sound "in.wav")))

        (let ((readers
                (list   (make-sample-reader 0 insound 0)
                        (make-sample-reader 0 insound 1) )))

        ; make sure the outsound is selected so LADSPA can write to it
        (select-sound outsound)

        ; execute the ladspa plugin
        (apply-ladspa readers
                        (list "amp.so" "amp_stereo" 0.5)
                        (mus-sound-frames "in.wav")
                        "applying amp_stereo")

        ; free up the reader buffers
        (for-each (lambda (r) (if r (free-sample-reader r))) readers))

        ; write outsound to disk
        (save-sound-as "out.wav" :sound outsound)

        (close-sound insound)
        (close-sound outsound)
)
(exit)