[LAU] ecasound/nama signal path queries

James Mckernon jmckernon at gmail.com
Tue Mar 6 22:43:06 UTC 2012


Hi all,

I have a few questions about using ecasound and/or nama with slightly more
complex, 'non-linear' chains of audio effects. By this I mainly mean
'forking' chains - such as highpassing a signal and applying a delay loop
to the high-frequency components of the sound, and a distortion to the
rest, for example.

This kind of thing would generally be straightforward enough to implement
in hardware with physical cables, but elegant implementations in DSP seem
rarer -- at least in linux. One of the reasons I am interested in ecasound
is that I gather from its 'examples' webpage that it handles exactly this
kind of thing quite elegantly:
'Ok, let's next do some parallel processing: two chains are created and the
input and output files are connected to them. As a result, the input signal
is processed with two sets of effects, and then mixed back together. You
can create as many chains this way as you want.' (
http://www.eca.cx/ecasound/Documentation/examples.html#effects)

However, I suspect that ecasound in its raw form could be somewhat unwieldy
for the sort of work I'd like to do, so I'd like to be able to use nama
instead. Would this sort of 'forking' signal chain be as easy to set up in
nama as it seems to be in ecasound? Also, in nama, is it possible/easy to
adjust and play with the effects path (and effect parameters) on the fly,
without interrupting playback?



Relatedly, another thing I'd like to be able to do is a delay effect, with
effect(s) (i.e. filters or certain kinds of distortion, followed by a gain
reduction) applied 'inside' the delay loop, such that the effect is
recursively, cumulatively applied to the looped material. Might sound like
a strange requirement, I know, but it's actually a fairly central effect to
the kind of music I'd like to make (dub reggae). Unfortunately, this is
difficult to achieve easily in Linux. Since no delay plugin that I know of
includes the kind of internal effects that I want, the only way to achieve
this is with some kind of 'circular' DSP chain, which most programs don't
allow. Does anyone know if this kind of 'circular' DSP chain might be
achievable in any way in ecasound - for example, by feeding a track's
output back to itself?

Any tips on achieving either of the above with other programs welcomed,
too! Thanks, all!

James
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