Subject: Re: Feedback in LADSPA (was Re: [linux-audio-dev] New LADSPA Version - Issues Resolved?)
From: David Olofson (david_AT_gardena.net)
Date: la maalis 11 2000 - 23:07:39 EST
On Fri, 10 Mar 2000, Jarno Seppanen wrote:
> David Olofson <david_AT_gardena.net> writes:
>
> > On Thu, 09 Mar 2000, Jarno Seppanen wrote:
> > > > Feedback loops in the host's network are beyond the scope of this API. The
> > >
> > > Stressing out: this does not need changes in the current API!
> >
> > Not completely true, if the feedback delay time is to be accurate.
>
> What do you mean by accurate? It is sample accurate in the sense that the
> user knows how much additional pure delay will be in his loops (that's always
> exactly one buffer's length, provided that the plugin execution order is
> appropriate).
"Accurate" as in "the user will not see random latencies depending on
what plugins he/she uses".
> Who defines the "ideal" or "desired" delay inside a feedback? We, as
> programmers, don't! It's the *user* who defines how much delay he wants. And
> the user cares only about the sound the thing produces.
Exactly. That's why the host should be able to compensate for the
inherent delay of plugins, so that the user won't have to do that by
hand, as in systems that believe that plugins have no delay.
> > Plugins have to specify a processing delay value. Sounds pretty
> > simple, but there is one problem; the delay may depend on control
> > inputs...
>
> All in all, this would only be needed in order to tell it to the user. Or how
> would you utilize such values otherwise?
To allowing the user to specify the feedback loop delay and actually
*enabling the engine to set it up*. Without plugins telling the host
about their internal delay, the user will have to tune every setup to
the desired feedback delay by hand.
> You could only tell the user the
> exact number of samples your feedback signal is delayed, but I argue that the
> user doesn't care.
Samples is not an issue... As you cannot handle feedback exactly as
in analog systems (where it is the actual delay of the processing
modules that define the feedback delay), the most intuitive
compromize should be used. This is certainly *not* something that
depends on the current buffer size of the engine.
//David
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