num/denom v's double (was: Re: [LAD] [ANN] LV2 beta3)

[Loki Davison]

On 5/30/07, Lars Luthman <lars.luthman at gmail.com> wrote:
> On Wed, 2007-05-30 at 10:30 +0100, Steve Harris wrote:
> > On 26 May 2007, at 18:05, Dave Robillard wrote:
> >
> > > On Fri, 2007-05-11 at 18:24 +0100, Steve Harris wrote:
> > >> On 11 May 2007, at 15:07, Fons Adriaensen wrote:
> > >>> On Fri, May 11, 2007 at 03:33:04PM +0200, Lars Luthman wrote:
> > >>>
> > >>>> That sounds like a good argument for two ints to me. Although
> > >>>> you'd have
> > >>>> to do a lot better than double if you wanted to represent
> > >>>> irrational
> > >>>> numbers in binary form. =)
> > >>>
> > >>> Two 32-bit ints can represent (the non-integer part of) most (not
> > >>> all)
> > >>> irrational values to better precision than a double. The algo to
> > >>> find
> > >>> them is a bit mysterious but very simple. Simple example: 355/113 is
> > >>> equal to pi with a relative error of less than 1e-7, not bad for two
> > >>> 3-digit numbers. It's not difficult to find two 32-bit ints that
> > >>> would
> > >>> be better than a double.
> > >
> > > So, what's the verdict on this?
> > >
> > > Don't want to fall into the perpetual beta with known issue trap, I'd
> > > like to fix the sample rate issue and crank out another beta ASAP..
> > >
> > > I'm skeptical we'd ever actually see a plugin that would use rational
> > > sample rate, so I vote double unless:
> > >
> > > - rational is required for perfect video sync over long time frames
> > >
> > > - someone can provide a concrete example of a realistic plugin that
> > > would require/benefit from rational
> >
> > Agreed. And no-one has to my knowledge.
> >
> > Multirate processing would require an extension, so that extension
> > may as well add the num/denom format for the sample rates as and when
> > it's needed.
>
> Unless you count internal filter banks with lower samplerate for each
> band (to save memory and CPU, since they have lower bandwidth than the
> total signal). But I don't know enough about multi-rate processing to
> suggest an actual example.
>
>
> --ll
>


mmm. This isn't really an example for the num/denom format but I used
to run my physical synthesis ladspa plugins with low sample rates as
you could control sample rate as a way of controlling wave speed. It
also made the processor load a lot lower. Using these in jack
environment where your actually doing anything else would possibly be
an example but you can do the multirate code in the plugin instead of
the host though just as easily. I can't think of another use but i
don't know anything about video stuff.

Loki