[linux-audio-dev] Fwd: Re: Sidechains, was Re: [linux-audio-announce] [ANN] swh-plugins 0.3.4

Steve Harris S.W.Harris at ecs.soton.ac.uk
Fri Jan 10 04:35:00 UTC 2003


Sorry, replied direct to Robert, not list.

----- Forwarded message from Steve Harris <S.W.Harris at ecs.soton.ac.uk-----

Date: Fri, 10 Jan 2003 09:25:32 +0000
From: Steve Harris <S.W.Harris at ecs.soton.ac.uk>
Subject: Re: Sidechains, was Re: [linux-audio-announce] [ANN] swh-plugins 0.3.4
To: Robert Jonsson <robert.jonsson at dataductus.se>

On Fri, Jan 10, 2003 at 09:47:26 +0100, Robert Jonsson wrote:
> >SC4 is more-or-less like SC3, but has no sidechain and a subtly different
> >algorithm. The sidechain was confusing hosts.
> >
> 
> Yes, I was wondering how the 3<-->2 port sidechain compressor plugin 
> would be handled in hosts...

The answer is 'badly'. ;)
 
> What if the sidechain was a separate ladspa plugin that in turn uses 
> some ipc mechanism to communicate to the plugin being controlled?
> I have no idea what kind of ipc is best for this, named pipes seem easy 
> but they are probably slow, yes?

Pipes are non-deterministic, so banned in LADSPA. The only one thats an
option is shared memory.

> By using one of the controls of the ladspa plugin to select which 
> sidechain "channel" (e.g. 1-10) they should send and receive on (much 
> like a comm-radio) you could have several different sidechains up and 
> running simultaneously.

Its an interesting idea.

> This construction has a number of interesting side effects (pun not 
> intended):
> * 1-n setups can be produced, one sidechain can control several effects.
> * Atleast with named pipes the control would be application agnostic.
>   The sidechain would not need to be used in the same host as the effect
>   plugin.

The same is true of SHM, but if the hosts are not running in sample sync
all hell will break loose.

> * I don't know if other types of plugins are applicable to this, but
>   since the sidechain is a separate plugin you could make _any_ plugin
>   sidechain aware. mmmm audio controlled room-size  for reverbs...mmmm
>   :-D.

Ahh, theres a misundersantding about what sidechains do here, they really
are just an audio stream.

> Any thoughts?

Neat idea. Kinda evil though. Very tempting...
 
> Top priority is a LADSPA stereo delay, I couldn't find one in Steves 
> collection.
> But it would also be nice with:
> - stereo autopanner
> - auto sweeping filters.
> Apologies if these infact are available and it's just my poor eyesight.

What do you want from a stereo delay? There is an left-centre-right delay,
but thats actually a mono delay that takes stereo input and pans the
result. A stereo delay would be easy to implemnt, what controls do you
want?

There is an auto-phaser (sweeping allpass filter), but no auto wah
(sweeping bandpass), or auto panner, true. I tend to build things like
that out of SSM or pd. But there should be complete plugins.

- Steve



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