[Stk] SKINI AfterTouch & ChannelPressure

[Carlos Pita]

Thank you. It makes sense for me now, altought the
the Errata in ChannelPressure specification
(http://www.borg.com/~jglatt/tech/midispec/pressure.htm)
explicitly distinguish between AfterTouch and
ChannelPressure characterizing the first
as per-key pressure (what you call Polyphonic
AfterTouch) and the second as per-channel
average pressure. So it leaves no margin
for interpretation, it's defining things
in a different way that SKINI constants do:
  MIDI AfterTouch != SKINI __SK_AfterTouch_
I'm pretty newbie to MIDI so I don't know
about de facto terminolgy usage but anyway
your explanation is clear to me.
Regards,
Carlos

> Carlos,
> 
> Different interpretations of the MIDI spec call these two
> things differently.
> 
> But the basic idea is that there is Channel Pressure,
> often called After Touch, which affects all notes
> currently sounding on that channel.
> Almost every MIDI keyboard that has After Touch
> implements this, because it's cheaper than Poly.
> AfterTouch is most often taken to mean Channel
> Pressure, hence the overloading in SKINI.
> 
> Poly Pressure, sometimes called Polyphonic AfterTouch,
> allows aftertouch to be sensed and sent from each individual
> key on a keyboard.  So if I'm sounding a C major chord
> and press on the E, only the currently sounding E would
> be affected.  Very few synthesizers and controllers
> implement poly pressure, but some do.  In STK it's called
> PolyPressure.
> 
> The extra alias of AfterTouch into Controller 128 (not a
> legal MIDI controller number, but a legal SKINI controller
> number) was a hack so that the .tcl scripts could use the
> same ControlChange function for all sliders.  It's a hack.
> 
> PRC
> 
> On Mon, 9 May 2005, Carlos Pita wrote:
> 
> > Hi! I can't make sense of the following equalities
> > (left side taken from MIDI specification at
> > http://www.borg.com/~jglatt/tech/midispec.htm,
> > right side from SKINI.msg):
> >
> > 0xa0 (AfterTouch) == 160 == __SK_PolyPressure_
> > 0xd0 (ChannelPressure) == 208 == __SK_AfterTouch_ == __SK_ChannelPressure_
> >
> > Why are you treating AfterTouch (individual key pressure)
> > and ChannelPressure (average channel pressure) as the same
> > thing and mapping them to MIDI ChannelPressure? And
> > what do you mean by PolyPressure and why is it mapped
> > to AfterTouch?
> > Is the rationale that PolyPressure gives the individual
> > key pressure while AfterTouch aka ChannelPressure should
> > be considered per channel pressure? If it is this way,
> > I find it very confusing, as it not only renames MIDI
> > messages but also refers to a different thing than MIDI by
> > AfterTouch.
> > Then there is AfterTouch_Cont, that is, AfterTouch
> > seen as a control. What is the role of AfterTouch here:
> > x key or x channel? What is the point of having it
> > again as a control (I noted that instruments in the
> > stk distribution prefer AfterTouch_Cont control over
> > AfterTouch message) ?
> >
> > Thank you in advance.
> > Regards,
> > Carlos
> >
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