[sdiy] MIDI velocity

[Ullrich Peter]

Hi Richie!

>1. Is it reasonable to expect that I could use a low-end micro (e.g. PIC) to scan a 61-key Fatar velocity sensitive keyboard with sufficient velocity resolution to work well?  Or does >it need dedicated hardware to measure the time between top and bottom switch closures for every key in parallel with sufficient resolution.  For instance the old E510 is >quoted as having 128us resolution, and it sounds challenging to write a program to poll all
>61 keys nearly 8000 times a second?  Obviously I can use a free-running timer, and subtract time stamps obtained from the top and bottom switch closures for each key, but it >still sounds tight.  I couldn't find any online examples of PIC based DIY velocity sensitive keyboards, and most commercial keyboards seem to have an ASIC taking care of timing >the switch closures and reporting results to a general purpose micro to form the MIDI packets.

If a simple midi channel 0 only design is enough then you could use the keyboard chip from the Crumar bit one. It is a simple 8751 chip that outputs midi data and it is velocity sensitive. But you can only use it if it's a DIY project - so no commercial project... I have the binary on one of my PCs - so if you can program these chips this could be a solution for you.
The keyboard schematics can be found on page 3 of this service manual:
http://manuals.fdiskc.com/tree/Crumar/Crumar%20Bit%20One%20Service%20Manual.pdf

>3. How should a receiving synth set it's voice's volume depending on the velocity byte received?  I tried to think through the physics of someone hitting a piano key with a >specific velocity, what the energy is from
>0.5mv^2 etc, and how that should influence the amplitude of the resulting sound wave.  It seems that most synths either have a linear response or an
>x^2
>response curve to velocity, but many offer a selection of different responses.

As all instruments have their own interpretion some master keyboards have different velocity curves they send out.
I designed a velocity converter that in principles has some tables with different curves in it to convert from one velocity "feeling" to another.

Ciao
Peter

http://www.ullrich.at.tt        (My homepage)
http://synpro.heimat.eu/datadial.htm    (Synth addon)
http://rc100-usb.at.tt/     (Roland sampler tool)






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