[ardour-users] bypass/activate plugins with automation?

Sampo Savolainen v2 at iki.fi
Tue Feb 14 00:02:36 PST 2006

Quoting David Slimp <rock808 at gmail.com>:

> Am I missing something?
> I'm not seeing a way to bypass/activate the plugins with automation.
> at a certain time, I want to stop one plugin and start another on the
> same track.

In fact. You are missing something. :)

This is not possible at the moment, and probably won't be. This is not
really a limitation in ardour's code, but a fact of life in signal processing.

Say you have a track where you use a compressor. You have loads of make up
gain dialed in the compressor. When you activate the plugin mid-signal, the
compressor's make up gain will make a non-linear jump in the signal:
crackles, in the basic sense.

A compressor is still a simple case, as they don't inherently cause latency
to the signal. But let's say the plugin is a convolution reverb which uses
FFT in it's processing, thus delaying the signal by the amount of frames
used in the FFT window.

What happens to the signal when you activate the plugin mid-stream? Does the
plugin spew out a zero signal for the duration of the FFT window? What
happens when you deactivate the plugin mid-stream? The stream would jump
forwards FFT window size samples. In both cases we would be producing nasty
non-linearities, and not what you would want it to happen.

This probably can be circumvented by making hacks in the code like running
the same stream through both without and with the plugin and crossfading
them. But I don't feel A) the workload is justified or B) that the end
result would even be what people want.

There are much simpler ways of doing this: Use multiple tracks or automate a
value which in effect turns on/off the plugin you would want to activate or

A track means a certain path of effects: if there is audio on a track where
you want radically different effecting, why not make another track? It's not
like you'd be "running out of tracks" in ardour.. :)


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