[linux-audio-dev] XAP: Some thoughts on control ramping

[David Olofson]

On Tuesday 21 January 2003 10.18, Steve Harris wrote:
> On Tue, Jan 21, 2003 at 05:09:34 +0100, David Olofson wrote:
> > For example, setting the initial level of an envelope and then
> > setting up the delay or attack phase won't work, unless you wait
> > for one frame before sending the RAMP event for the delay or
> > attack phase. Similarly, an attack duration of 0 would result in
> > the decay starting at the current value, instead of the attack
> > peak level.
>
> Yes, you're right. Damn.
>
> OTOH If we define that RAMP events arring in the same timestamp for
> the same control override each other then it becomes the hosts job
> to normalise them (not a hard task).

It's not hard, but I didn't like the way it looked in Audiality's EG, 
and I don't like the logical glitch that is a broken duration 0.

With only RAMP events and RAMP(value, 0) as a special case on the 
receiver end, the EG code is nice and simple, and the receiver end 
if() is trivial.

I could just test for 0 duration in the EG, but the only really 
straightforward solution would be to delay for an extra frame, which 
would effectively make a 0 duration stage take one frame too many ==> 
timing error build-up. Then I would need to shorten the next section 
by 1 - but what happens if the next section is 0 or 1 frames...?

I don't feel like I need that when I'm adding multiplication with 
ramped input - and this is still pretty basic event processing! :-)


> Envelope sections with 0 duration are often not provided anyway.

They definitely generate nasty clicks, but setting the initial level 
of an envelope higher than 0 generally doesn't, unless the waveform 
starts with a click. Anyway, this isn't as much of an issue as the 
special-casing needed in senders, I think.


//David Olofson - Programmer, Composer, Open Source Advocate

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