[sdiy] Aftertouch via Pressure

[Glen]

At 05:39 AM 7/9/03 , jhaible at debitel.net wrote:

>But the mechanical part is difficult. You must find a way to insert
>the tube (hose?) beneath the keys, such that it's equally actuated from
>blacks's and white's. And, worst of all, you have to find a way to
>get enough key travel even with the additional thickness of the
>tube. But then again, the SH-2000's keyboard also has reduced 
>key travel, and it plays nicely ...

Mount the back edge of your keyboard assembly on a hinge, possibly piano
hinge (that eliminates any alignment problems of multiple small hinges.)
Place the front edge of your keyboard assembly over the sensor hose (which
would run from left to right, underneath the whole keyboard.) The front
edge would need some springs added to help hold the keyboard assembly down,
just in case your instrument was ever turned upside down--possibly when
being transported. You might even add some "return" springs underneath the
front edge of the keyboard to ensure that the keyboard would move back up
to its proper resting position after you stop pressing down on it. The
rubber hose underneath the front edge will provide a spring effect of its
own, but this will probably need to be augmented with such actual springs.
Using return springs also allows you to use a more flexible and more
sensitive type of tubing underneath the keyboard assembly. This should give
you a more sensitive assembly that needn't be pressed so hard that you
think you are going to break something, just to get some after touch. (My
Kawai K4 has after touch, but is far too stiff and insensitive for my
taste. I feel like I'm going to break something just trying to activate the
after touch.) If you mount your whole keyboard on a hinged sheet of stiff
metal (sort of a sub-chassis), you could even move the tubing away from the
front edge of the keyboard. This would allow for adding more pressure to
the hose, for a given amount of applied downward pressure, at the expense
of having to press the keyboard farther, due to leverage effects. (I hope
you know what I mean by this.)

All of this assumes that you only want to develop a global pressure
parameter, and not have individual after touch sensors underneath each key.
If that's what you really want, it's going to get a lot more complicated.

I look forward to hearing from other Synth-DIY members, as I haven't
actually seen a keyboard built like I'm describing, but I think it should
work. Let me know what you think. The advantage of my technique is that it
does not screw around with your keyboard's key action--just the keyboard
assembly mounting. The keyboard's keys should play with the same "feel"
that they always have.


later,
Glen Berry