[linux-audio-dev] XAP: a polemic

[David Olofson]

On Wednesday 18 December 2002 11.51, Steve Harris wrote:
> On Wed, Dec 18, 2002 at 11:22:44 +0100, David Olofson wrote:
> > It's not very hard to do for basic stuff, and it means many
> > plugins won't need any internal filtering at all.
>
> Unlikly. Most plugins will only render the control values ever 32
> samples (say) and then will just use linear sections between those.
>
> I think providing all that specification is a mistake, its quite
> complex and will not be usefull most of the time.
>
> > Many effects will make this audible, and thus, will need to
> > implement filtering internally anyway. Splines can probably
> > eliminate this in most cases.
> >
> > We should probably try it though. Anyone around here has real
> > experience with this?
>
> Splines have some unfortunate side effects, like excursions, which
> make them only suitable for a small number of cases. Also the
> calcuation cost means they have to be used sparingly.
>
> The place the're most useful is where you have high bandwidth, low
> rate of change values, eg. in internal ringbuffer pointers. You
> wouldn't want to use them on external controls very often.

Right. I've mentioned that you're really meant to deal only with the 
current block, and thus, we're *not* talking about low rates of 
changes. (BTW, AudioUnits also does it this way, if I understand it 
correctly. You have to keep telling the receiving control about the 
ramp for each block.)


> Also, remember that most of the time the controls are going to come
> (ultimatly) from the user moving a slider around (etiher real or
> GUI) its not easy to generate good splines from that data. Ramps
> are much more practical, and more convienient for the DSP
> programmer.

All good points.

It seems to me that we should do like everyone else: Linear ramps 
only. Dead simple (well, almost), well defined and *very* much better 
than no ramps at all.


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

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