Topic by groovy

  • Avatar
  • groovy
  • Member
  • Offline
  • Registered: 12-06-2009
  • Posts: 717

Topic: Real velocities?

Hello,

I had an idea to estimate the real speed a pressed key has and how it is related to the midi velocity.

All I needed was a flat piece of wood, a coin and Pianoteq's midi-eventmonitor.

http://fs5.directupload.net/images/170218/4prxturv.jpg

With this wooden "tool" I can press three white keys at the same time. Because a ten eurocent coin is 1.93 mm thick, the note-on event of the key below, here c3, happens a little earlier than note-on of d3. The distance of 1.93 mm divided by this eventtime-difference is a rough estimation of the speed of key c3.

Example:
30729 ms Note On C3 veloc: 75
30736 ms Note On D3

ds = 1.93mm
dt = 7ms
keyspeed = ds/dt = 1.93mm/7ms = 0.276 m/s

This velocity 75 and keyspeed 0.276 m/s are representing one point in the graph. I set a linear trendline in libreoffice, but many other curves would fit, so I'm not sure it is really a linear relationship in the Kawai. I have to test a few more keys because those rubberbubble-contacts are prone for high tolerances.

http://fs5.directupload.net/images/170218/h26yfcta.png

From midi velocity 60 upwards the method is getting unprecisely. The highest resolution in PTQ's midi-eventmonitor is 1 ms and the faster the keys are pressed, the nearer dt comes to this limit.

Thanks for your interest

Reply by groovy

  • Avatar
  • groovy
  • Member
  • Offline
  • Registered: 12-06-2009
  • Posts: 717

Re: Real velocities?

... hm, seems to be linear with another key too (here c2):

http://fs5.directupload.net/images/170219/96zrnp7i.png

If a key would be massless, a linear speed to velocity conversion seems to be a good construction. But a real key has a mass, that has to be accelerated to reach a given velocity. And acceleration against inertia needs a force F=m*a. That could be an explanation, why I use and prefer my s-shaped curve to the default linear velocity mapping:

http://fs5.directupload.net/images/170219/goqwnlpj.png

Such a shaped curve makes the key virtually "heavier" in the ppp-mp range, where inertia is low, and virtually lighter in the mf-fff range, where F=m*a is stronger. As a result the keyboard response "feels" linearly balanced.

A question could be, whether an s-shaped curve can be derived/calculated somehow from the measured key-speed function and F=m*a. Any ideas or show-stoppers welcome ...

Reply by julien

  • Avatar
  • julien
  • Admin
  • Offline
  • Registered: 19-04-2007
  • Posts: 1,000

Re: Real velocities?

Wow this is really a great idea ! Very smart, indeed.

julien's Website

Reply by Mossy

  • Avatar
  • Mossy
  • Member
  • Offline
  • Registered: 22-01-2014
  • Posts: 200

Re: Real velocities?

I had to read the message 3 times before I realized the coin had to face down.  I kept trying to visualize out how the difference was calculated with a piece of wood across 3 keys and the coin on top.

https://soundcloud.com/mossy456/

Reply by bSharpCyclist

  • Avatar
  • bSharpCyclist
  • Member
  • Offline
  • From: California
  • Registered: 22-08-2016
  • Posts: 31

Re: Real velocities?

Cool idea. I don't use an S curve, but something similar I guess. I clip the bottom at 20 and the top at a 105, linear in between those two points. Seems to be OK with my YDP-181.