Re: [LAU] ecasound/nama signal path queries

On Tue, Mar 06, 2012 at 10:43:06PM +0000, James Mckernon wrote:
> 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?

Hi,

With Ecasound, you can change effect parameters without
interrupting playback.

Adding and removing effects can create a pop, which Nama
hides by briefly muting the track.
 
Changing effect parameters can also change effect latency,
which would create a pop. Nama doesn't protect you in that
case.

The first example of signal processing you give is easy to
do, presuming you've spend a little time to learn the Nama
or Ecasound ways of doing it!

> 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.

You may have to roll your own.

> 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?

I haven't seen an example with Ecasound.

Regards,

-- 
Joel Roth
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