EDWARD.STAUFF@OFFICE.WANG.COM (Edward L. Stauff) (12/01/90)
Dave Kenny (among others) wanted to know how I built a velocity-sensitive pedalboard. Velocity is quite easy to implement, regardless of whether it's a manual keyboard or a pedalboard. All you need is two switches for each key, and a means of measuring the time delay between the two switches changing state. One switch opens or closes near the top of the key travel, the other opens or closes near the bottom of the key travel. I interfaced my key switches to a PC with an extremely simple I/O mapped scheme; I'd rather futz with software than hardware. My software scans the key switches and notices when a switch changes state, and measures the time delay between a key's top switch and bottom switch. A little experimentation showed how to translate the time to a MIDI velocity value. The hardest part was getting a counter to increment fast enough; Int 08 isn't fast enough. I ended up getting some code (which I don't fully understand) that uses the CMOS clock or something like that. Does anyone know if any synth manufacturers use a different method for sensing velocity? Just curious. Also, does anyone know how (in detail) to do polyphonic aftertouch? I've heard that you put a piezo-electric something-or-other under each key, but I'd like to get more detailed info on how to do it. And now, an update on pedal velocity, beginning with a relevant digression: For many years I played organ in stocking (or sometimes bare) feet. Eventually I studied with a teacher who required that I wear shoes, arguing that (proper) shoes give one better control. I always disagreed with this, but complied. Recent empirical studies have shown that pedal velocity does seem to be somewhat less difficult to control with shoes. My feet are starting to develop sensitivity to velocity when playing slow passages. Fast footwork, on the other hand, seems to consistently max out the velocity. Actually, the most intractable problem I've encountered so far is how to control sustain when my feet are busy! -- Ed Stauff Edward.Stauff@OFFICE.Wang.com