[sdiy] Beat timing calculations

[Joel B]

Thanks Andre, this was very helpful.

I replaced my:

persecond=60/tempo
interval=persecond*1000

with 

interval=(60/ tempo) / 4 *1000

and things are working a lot better now. I'll try switching to double precision as well, see if that improves things.

I don't at the moment have access to the sample-clock, I only have a millisecond counter.  


Thanks to the other posters as well!

 - Joel





On Jul 27, 2011, at 1:49 AM, Andre Majorel wrote:

> On 2011-07-26 21:02 -0700, Joel B wrote:
> 
>> I'm contemplating writing a drum machine like program and i'm
>> not sure how to calculate the timing to trigger a note, say a
>> 16th note pattern, for instance. Here is what I have so far:
>> 
>> 130 bpm= bps=60/130=0.46153846 
> 
> Yes.
> 
>> 1000ms per second * bps 
>> ms =461.53846  per beat division
> 
> Yes.
> 
>> 16 beats=16*461.53846 =7,384.61536
>> Milliseconds per loop
> 
> What ?
> 
> If by "16th note pattern" you mean a whole 4/4 bar of 16
> semiquavers, a semiquaver is 1/4th of a quarter note so about 60
> / 130 / 4 = 0.115 s and a whole bar lasts about 60 / 130 * 4 =
> 1.846 s.
> 
>> but there probably has to be something to handle things that
>> don't land on a proper digital boundary like 33.3333333333...
>> without throwing the tempo off with rounding or truncation
>> errors?