Re: [ecasound] changing filter cutoff on the fly

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Subject: Re: [ecasound] changing filter cutoff on the fly
From: Kai Vehmanen (
Date: Tue Oct 05 1999 - 12:29:19 EEST

On Mon, 4 Oct 1999, Kali Griffin wrote:

> I made an eca app that just does low-pass filtering from one of the
> ecatool examples. my question is this, is there a way to change the

If you want to change effect paremeters without interruptions to
processing, you'll have to use controllers (=oscillators).
1.6.x will offer routines for changing parameters in realtime and
through ECA_PROCESSOR interface. This is high on my priority list,
as ecasound and qtecasound desperately need this feature, too.

> filter cutoff on the fly without respawing the eca program? or do I have
> to crash it?

If you need to control the processing from outside, you should use
ECA_CONTROLLER. So instead of...:

-- scenario 1 --
ECA_SESSION esession;
ECA_CONTROLLER ctrl (&esession);
[... other setup functions ]
ECA_PROCESSOR p (&esession);
p.exec(); // blocks until processing is finished

-- start the processing with:

-- scenario 2 -- [... normal setup as in scen1] ctrl.start(); // doesn't block --

The third way to use is to use ECA_PROCESSOR directly...:

-- scenario 3 -- ECA_SESSION esession (COMMAND_LINE& obj); ECA_PROCESSOR p (&esession); p.exec(); --

There might be better ways to organize these classes. Hmm, I don't know, does this seem confusing to you? And of course, you can bypass the ecasound base-classes altogether and use individual classes directly. So...:

-- scenario 4 -- - create a SAMPLE_BUFFER object for storing the samples - read samples with (for example) using WAVEFILE - process them with EFFECT_LOWPASS - maybe change filter-freq with EFFECT_LOWPASS::set_parameter(1, new_value) ... - write samples to OSSDEVICE --

-- Kai Vehmanen <> -------- CS, University of Turku, Finland . - linux audio processing . - ambient-idm-rock-... mp3/ra/wav

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