From: mrk@gvgspd.GVG.TEK.COM (Michael R. Kesti) Subject: Re: Polyphonic aftertouch Date: 31 Dec 90 05:26:25 GMT Aftertouch, sometimes called pressure, is a MIDI control that is typically created by keyboards that sense how hard the user continues to press the keys after the initial presses. It differs from velocity sensing in that the user can alter the pressure while holding the note(s), whereas velocity is determined, and transmitted, once per key press. Aftertouch messages are sent anytime that a change in pressure greater than some threshold is detected. There are two types of aftertouch: channel and polyphonic. With channel aftertouch, the instantaneous pressure value is the average (or sometimes greatest) of the pressure of all keys currently pressed. Polyphonic aftertouch provides the means to transmit a unique pressure for each key. You can see that polyphonic aftertouch has a greater potential for adding to the MIDI clutter we have recently discussed. The aftertouch functions are allocated unique status bytes. The message formats are: polyphonic aftertouch: 1010nnnn 0kkkkkkk 0ppppppp channel aftertouch: 1101nnnn 0ppppppp where nnnn = channel number kkkkkkk = key number ppppppp = pressure >> My Roland U-220 supports it, but my Yamaha V50 doesn't seem to support it. This means that if your controller (the V50) were capable of generating aftertouch, your U-220 would be able to use this data to modulate the sounds being generated. Note that auxiliary controllers, such as the J.L. Cooper Fadermaster are capable of generating aftertouch (channel only, in this case) and may therefore be used to provide realtime modulation control of your U-220. Finally, note that keyboard controllers might have neither velocity nor pressure sensing, either velocity or pressure sensing, or velocity and pressure sensing, although I am not aware of any that feature pressure sensing without velocity sensing. ============================================================================ Michael Kesti Grass Valley Group, Inc. | "And like, one and one don't make mrk@gvgspd.GVG.TEK.COM | two, one and one make one." !tektronix!gvgpsa!gvgspd!mrk | - The Who, Bargain