MIDI Kinetics Forum

According to Macciza'a link though, even my second question (original post) now has a different answer. The unofficial info i found states that an average is calculated while the official spec clearly states that the greater pressure value of all keys pressed is sent (when talking about mono-aftertouch/channel pressure).

Phil999 wrote:yes, there are two kinds:

a) monophonic aftertouch. AKA channel aftertouch. Every middle-class keyboard has it. One parameter is sent, regardless of the key number.
b) polyphonic aftertouch. AKA key aftertouch. Only few high-end keyboards have it. It's expensive, because each key has an individual pressure sensor.

Now, for the question: I don't know how real keyboards featuring b) send poly AT values; I planned to get such a keyboard, but never got one unfortunately. Yeah I also guess it goes to zero after release.

perhaps you know-have investigated what happens in a)? I mean after releasing a key (lets say we pressed only one) what happens to channel pressure? Jump to 0, ramp down to 0 or no message at all?

Yeah . . . Release Velocity is one of those messages not widely supported, just like Poly Pressure, and presumably for similar reasons - cost to build individual sensors per key. Thinking about the hardware for a second, it's likely that the same sensors would be useful for sensing both values.

However, and here's where you might score big - I'm not sure your VST has to support RV so long as you DAW does, and can map / assign this to whatever parameter you wish to control.

This is what I used to do back in the good old Atari Cubase days to gain some extra realtime controllers - ironically using channel and poly messages painted into the key editor. I was fortunate enough to have a rack workstation synth that responded to poly, although of course I didn't use it as intended (as it was clearly intended to take the everloving p*ss out of MIDIs bandwidth).

Softcore wrote:perhaps you know-have investigated what happens in a)? I mean after releasing a key (lets say we pressed only one) what happens to channel pressure? Jump to 0, ramp down to 0 or no message at all?

I don't know either. Both masterkeyboards I bought in the last years do not feature AT, not even mono AT. That wasn't very wise. I once had a PPG PRK FD which surely had mono AT, but it stopped working eons ago unfortunately. Mmmh, really. Such a nice keyboard it was. On top of it, legend said it belonged to Andreas Vollenweider before, a good and famous musician which I adore very much. Sorry, I digress. Old memories.
Hmm, with this approach the poly AT values remain where they were left after release. I have no idea if this is of any help for you, for me it is the first poly AT template ever. Maybe I can use it some day. It would need some dynamic resizing like in the SynthX app to be a real useful keyboard controller, but I guess this won't be too difficult to make.

Hi
It is also one of those mis-named one . . . - it is a NoteOff / velocity message . . .
Same as with 'Aftertouch' - its Polyphonic Key Pressure and Channel Pressure . . Aftertouch is a nickname / advertising slogan

Physically there is a sensor that is affected by all the keys - this sensor generally outputs the largest (channel) pressure which is why that is the result you get . . . You would need poly key pressure sensing to average it out

Message flow would be something like NoteOn velocity, then varying values 0-127 as pressure varies , highest value used as fingers change, then final pressure value reduces to 0 before NoteOn vel 0 or noteoff triggered. . .
There is no other physical way to do it really. Notes can be on with Pressure of 0 and have to transit back to 0 before note offs are possible . .

Cheers
MM

I wouldn't call it misnamed - it is the correct name, though you're of course correct in that it isn't a separate parameter in its own right, rather the third byte in a genuine NoteOff msg.

All that aside, I feel the whole idea of using Pressure msgs from the iPad to be a bit . . . skeuomorphic? Just forget about the notion that it ought to behave like the real thing and embrace the idea that it can behave as you (dynamically) wish perhaps?

[edit]

Thinking about it . . . NoteOff Vel is probably how I saw this referred to more officially, Release Vel colloquially.

Well i didnt know that - about the Note off velocity - I might as well implement that too!

@Phil: Yeah, ufortunately I wasnt that wise either - I dont even have a monophonic aftertouch keyboard (channel pressure). I will send you my approach this afternoon since you are also interested in this!

Its a concept testing with ONE midi key sending note on (transposable via "octave selection" buttons), velocity and aftertouch (the monophonic one, channel pressure)

The thing is - and my thinking could be totally wrong on this of course - implementing NOV is probably as tricky as any of these other "what happens when I let go of the controller" CCs.

That is, you can technically implement them easily enough - but the hardware is different enough that they don't make a lot of sense in this context?

What I'm trying to say is, anything you can attach to these CCs for parameter-change could just as well be attached to any other CC (if indeed you need to use a fader or similar). On the other hand . . . there might be some sort of sensor apparatus on the iDevice that tracks the surface area of your finger when it's in contact with the screen - and if there is, and you can get access to it you can then calculate CP, PP and NOV with relative ease.

This will be a job for Liine to implement into the core app, if the sensor data is extant and available - but it would go a long way to bridging the gap between the hardware of a traditional keyboard and the touchscreen.

Anyone looking for a fairly cheapish way to experience (at the least) CP - the Novation Impulse line of controller kbds support it. Not fantastically well IME - but probably as much to do with the fact I'm no keyboard player as anything else.

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