[linux-audio-dev] PTAF link and comments

[David Olofson]

On Wednesday 05 February 2003 14.00, Sami P Perttu wrote:
> On Wed, 5 Feb 2003, David Olofson wrote:
> > Anyway, the reason for not using Hz or similar in the API is that
> > such units are harder to deal with, pretty much no matter what
> > you want to do. The only exception is when you actually want to
> > have some periodic action driven by it, ie sound. Thus, rather
> > than using Hz in the API and having event processors and whatnot
> > convert back and forth, we use linear pitch (1.0/octave)
> > throughout, and leave it to the final stage; the synth, to
> > convert it into whatever drives it's
>
> Okay, that is some kind of answer. The needs of the event
> processors outweigh the needs of the audio processors.

Not quite. It's only a matter of *where* to perform the conversion. It 
can never be avoided entirely. (Unless we assume that users will want 
to paint events in piano rolls with Hz on the vertical scale, that 
is. ;-)


> > oscillators. Which, mind you, is not necessarily Hz or
> > samples/period! It may well be coefficients for a resonant filter
> > you need.
>
> I guess you'd still convert them to linear frequency on the way.

Not if you're using an optimized approximation. That generally boils 
down to a plain polynomial or similar function, translating whatever 
you have directly into whatever you want.


> > As to actually doing the conversion, I suppose we could throw
> > some inline implementations into the plugin SDK.
>
> Yes, a control iterator would be nice: something that takes a pitch
> ramp event as input and then produces Hz values each sample as
> output.

Yeah, we can have all sorts of stuff like that. It's not really part 
of the API, so it won't be as hard to "get stuff in" - although it's 
obviously still a good idea to keep things nice and clean, and avoid 
obvious redundancies. After all, an SDK isn't of much help if it 
takes longer to find and/or understand what you need than it would 
take to implement it on your own.


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

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