[linux-audio-dev] XAP and Event Outputs

David Olofson david at olofson.net
Mon Dec 9 16:17:00 UTC 2002


On Monday 09 December 2002 18.59, Steve Harris wrote:
> On Mon, Dec 09, 2002 at 05:47:47PM +0100, David Olofson wrote:
> > 	* Hosts may chose whatever buffer size they want.
> >
> > 	* You may be running off-line, in which case you
> > 	  could potentially run with "huge" buffers.
> >
> > It still doesn't matter? I do believe concistency matters in
> > serious audio applications, so latency has to be *defined* - even
> > if not incredibly low.
>
> Sure, thats why I'm confused my your suggestion of changing the
> buffer size inside loops.

Well, unless you're already using a buffer size that's small enough, 
you'll have to switch to smaller buffers for the plugins involved in 
the feedback loop.

That explicit delay element I'm talking about would probably be an 
internal host object that's aware of the buffer size in the loop it 
sits in, and subtracts the corresponding latency from the delay 
parameter, so you get *exactly* the delay requested.


> > Well, one would assume that the host forbids feedback loops
> > without delay elements, so at least, the user cannot do this
> > without being aware of what's going on, to some extent. If the
> > buffer size goes below some sensible number, the host could warn
> > the user about potential CPU load increase. ("Read docs for more
> > info".)
>
> My experience is that this isn't neccesary. Genrally nothing really
> supprising happens in fedback systems, unless the blocksize is very
> large.

Well, most VST and DX hosts don't allow feedback loops at all, 
AFAIK... I wouldn't think it's a major loss, unless you're doing 
things that you *should* be doing on a modular synth.

But then again, why prevent XAP from reaching a bit into that field? 
In the case of feedback loop handling, it's actually entirely a host 
side issue, so there's nothing preventing some hosts from doing what 
I describe.

Indeed, you could most probably do that with VST plugins as well. 
It'll most probably be a bit more hairy and less efficient than with 
XAP, though!


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

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