[gmpi] Re: Ramps
- From: Jeff McClintock <jeffmcc@xxxxxxxxxx>
- To: gmpi@xxxxxxxxxxxxx
- Date: Tue, 11 Jan 2005 10:04:36 +1300
> I am confused anyway. Smoothed up to what degree? Can
> a plugin trust a host to "smooth enough"? What is
> "smoothed enough"?
This is not voodoo. This is not subjective. This is resampling.
Your MIDI CCs arrive at a known rate, perhaps 20Hz.
GMPI controls are sample accurate. Ramps are directly convertible to an
audio rate signal. Therefore GMPI ramps are an audio rate signal.
The correct smoothing is equal to the MIDI CC period. (in this case
1/20 = 50ms). No more, no less.
Converting MIDI CC to ramps is upsampling. Sampling theory is well
understood. When upsampling, interpolate between samples. Linear
interpolation is the simplest method, and translates directly to ramps.
CC's are about 1000 times slower than audio rate, but as an example,
lets upsample *2.
Original MIDI CC values:
1
2
3
Good upsampling...
1
1.5
2
2.5
3
Bad alternative, sending CC as 'point' updates. Is equivalent to
upsampling by repeating the same sample several times.
Upsampling via 'point' updates... (ramps with duration = 0 )
1
1
2
2
3
3
this is a stair step, the crudest resampling method.
Upsampling to ramps is very straight forward. You don't actualy
generate the in-between samples...you generate ramp events.
Event 1:
Time:0
End Value: 1
Duration: 50ms
Event 2:
Time:50
End Value: 2
Duration: 50ms
Event 3:
Time:100
End Value: 3
Duration: 50ms
etc....
50ms is just an example, a GUI for example generates updates at a higher
rate e.g. 50Hz. The host adjusts the ramping duration dependant on the
control source.
Best Regards,
Jeff
Crudesoft wrote:
At the risk of being silly and all that, but if it is
the host's responsability to smooth events, then why
isn't the requirement more explicit? Why not add
something to req. 25 like "Plugins may expect smoothed
events for their controls." and leave it up to the
plugins to smooth some more if they want to?
I am confused anyway. Smoothed up to what degree? Can
a plugin trust a host to "smooth enough"? What is
"smoothed enough"? Wouldn't a plugin smooth anyway
just to be sure? If so, then this req. doesn't make
anything any simpler and it would probably be better
to simply ditch it. (This has been proposed before,
but I haven't seen an answer.)
Crudesoft
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