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 Forum index » DIY Hardware and Software
Velocity sensitive keyboard?
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bigtex



Joined: Mar 30, 2006
Posts: 321
Location: Cupertino, California

PostPosted: Fri May 19, 2006 4:39 pm    Post subject: Velocity sensitive keyboard? Reply with quote  Mark this post and the followings unread

Hi all. I was just looking at Ray Wilson's keyboard projects and I got thinking about some keyboards I have. One of them is this older Casio CP-300, which was intended to sound like a real piano and not have a bunch of fancy "kid's toy" features. Well, it doesn't sound much like a real piano, so it's really of no use. Except that is is 61 full size keys and it is velocity sensitive. I could do a MIDI->CV conversion, but I'm thinking of tearing it apart, re-housing it in wood (just because) and making it a CV keyboard.

So, my real question is this: how hard is it to make a CV keyboard velocity sensitive?

This keyboard uses little membrane switches and probably looks at the timing between the keypress of the first and second switch (I'm just guessing it has two switches.. I haven't looked at it in a long, long time and I'm not at home now). So if this is the case, there must be a circuit that would convert the width of a single pulse into a velocity voltage, right?

Anyway, I'll probably think about this some more and see what I can work out, but I was just wondering if anybody else had done a similar project.
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elektro80
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Joined: Mar 25, 2003
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PostPosted: Fri May 19, 2006 5:22 pm    Post subject: Reply with quote  Mark this post and the followings unread

Trivia: velocity sensing is overrated for synths. Keep in mind that at least for live use and impros timbre/sound/filtering will be more important than polkastyle velocity stuff. A big mixer and various expressive signal routings using through compressors and reverbs and whatnot makes more sense than adding velocity sensing. It makes more sense to set up a footpedal rig in order to play filter parameters. You play the actual note events with your right hand, you use your left hand for playing the synth and you use your feet for playing the filter parameters. BTW: it is great fun to store various parameters in a sequencer and use your feet for stepping back and forth between settings.
Very Happy

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bigtex



Joined: Mar 30, 2006
Posts: 321
Location: Cupertino, California

PostPosted: Fri May 19, 2006 5:29 pm    Post subject: Reply with quote  Mark this post and the followings unread

You know, what I really want goes way beyond just a velocity sensitive keyboard. I'm really not even all that into veocity sensitivity or keyboards for that matter. But I took piano lessons when I was young, so it is a convenient interface for me.

Here's what I really want:
It would be something like a piano keyboard, but with bags of air under each key. The key would be springloaded or something so that the bag would re-inflate after pushing a key. The air let out by pushing down on the key could be short puffs or long, slow blows, or hard and fast bursts. Each key would then have a pressure transducer and a air velocity sensor to read these things. Changes in pressure and velocity would then be mapped to parameters. You could press a key down just a little bit and have it do something. I think that would be way more expressive and usefull.

I guess it could be done without air, but the air creates a nice feedback effect in the air pressure. But another way could have each key pivoting to be turning a potentiometer. You could use position, velocity, and acceleration of the key to control parameters. That would be much more fun. Forget about pushing the key all the way down to make a note. I want it to be more expressive.

....but... if I were to just try and turn my old Casio into a velocity sensitive keyboard, there must be a way that isn't too painfully difficult...
but maybe I shouldn't bother...
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elektro80
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PostPosted: Fri May 19, 2006 5:37 pm    Post subject: Reply with quote  Mark this post and the followings unread

I have had my piano lessons too. Very Happy Don´t misunderstand me, I,m all for the good old velocity stuff.

Why not get some very inexpensive secondhand midi controllers and add some midi to CV interfaces? You could add an old mac or PC with MAX or KeyKit for some midi processing. That way you could process the midi input into something really useable? Very Happy

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jksuperstar



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PostPosted: Sat May 20, 2006 7:07 am    Post subject: Reply with quote  Mark this post and the followings unread

I think the MIDI>CV is probably your least painful ticket for those keys. Handling those switches in an analog fashion would be terror, since they are designed to be scanned very fast, in order to get polyphony, etc. Not that you'd need that for your rack, but it's what they were designed for. So to scan all those switches and figure out which one was the trigger to the keys, well, you'd probably end up adding 61 resistors in a ladder much like typical mono CV keyboards do.

But, if you want something crazy, and don't *need* the feedback, this is probably the closest thing I've seen to your description:
http://www.electro-music.com/forum/viewtopic.php?highlight=continuum&t=1142
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bigtex



Joined: Mar 30, 2006
Posts: 321
Location: Cupertino, California

PostPosted: Sat May 20, 2006 9:58 am    Post subject: Reply with quote  Mark this post and the followings unread

Wow, that continuum controller is amazing. I'd sure love one of those but I just blew all my money on blacet stuff (which I'll get more use out of anyway).

I figured a MIDI->CV converter might be the right path, I just was curious about doing it without MIDI. Just for the sake of it. But considering the work that would likely be involved, and a result that probably wouldn't be worth all of that work, I'll just forget it. And like I said, I'm not even into keyboards all that much. They're just a convenient way to control something.

Thanks for the replies.
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toppobrillo



Joined: Dec 10, 2005
Posts: 766
Location: oakland, ca
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PostPosted: Sun May 21, 2006 2:36 am    Post subject: Reply with quote  Mark this post and the followings unread

heres an easy way to do it, mount piezo transducers to the plastic underside of where your keys hit. thats the way that EH did on their mini-synthesizer i understand. i guess theres about a million ways to turn that into data for your synthesizers...cheap but it might actually work OK so long as you isolate them from other bumps your kb may encountre.
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Yorky



Joined: Feb 14, 2005
Posts: 244
Location: Boston, UK

PostPosted: Thu Jul 27, 2006 10:30 am    Post subject: Reply with quote  Mark this post and the followings unread

It's easy, you have a spdt under each key, and the time it takes from leaving the top one to reaching the bottom gives you the velocity (shorter times = more velocity).
Since I only work in (mostly) analogue, I'd do this by holding a capacitor at 0V and allowing it to charge while the key is in motion, resultant voltage, inverted and made to correct level, goes to VCA, you can even have a pot across this voltage to give a 'velocity-sensitivity-ness' control on your panel.
There's more to this but that's the basic idea.

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