[linux-audio-dev] XAP: a polemic

David Olofson david at olofson.net
Sat Dec 14 21:56:00 UTC 2002


On Sunday 15 December 2002 03.25, David Gerard Matthews wrote:
[...]
> >I would like to clarify something here: musical time as used in an
> >API is not by definition "periodic". (That's just an
> > interpretation of it, normally based of the time signature.)
> >
> >The APIs that don't use audio frames for timestamps and song
> > position generally use "ticks". 1.0 per quarter note is a fine
> > unit, for example, if we (like practically everyone else) decide
> > to use the quarter note as the base. It's rather handy, because a
> > quarter note is always a quarter note, but a bar might be
> > anything...
>
> Well, not necessarily!  A quarter note is not always the unit of a
> single beat.

Well, I never said it was the unit of a *beat*. ;-)


>  In traditional
> music theory, 6/8 meter is frequently thought of in 2  - the
> dotted-quarter note gets the beat.

Well, yes - I've actually used that sometimes.


> Half-note based meters (2/2, 3/2) are also very common, and things
> like 5/16 are not
> uncommon in modern music.  That said, I think what you mean by
> quarter-note is
> what I would call "counting unit" or "durational unit" or something
> like that.

Yes. And either way, even if you never *use* a quarter note, or the 
corresponding distance, in your music, quarters, dotted quarters, 
16ths or whatever still have a fixed relation. Just tell the plugin 
to do 16ths, and it'll get the idea.


> >  while you can just modulate some audio with
> >(sin(musical_time * M_PI * 2.0) + 1.0) or whatever. ;-)
>
> Nice.  Sounds like fun.

Or maybe not...

	out = in * (1.0 - fmod(musical_time * 4.0, 1.0));

would be more fun, although you'd need some filtering on the 
modulator to kill that awfull clicking. Or just use it to index an 
interpolated "envelope waveform" of some 16 points or so. (*Now* it 
starts to get interesting. :-)


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

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