Inside stuff: Korg Kronos

Vitaliy_Kiselev

Photos via: http://si7-lab.blogspot.com/2011/06/cpu-of-kronos-is-d510.html

Main part of synth - Atom D510 CPU on Intel ITX motherboard

Alfi666

I have a Roland from 1996 :) ... was always wondering how they did the Velocity sensing on keyboard... is it done with pressure sensors?

Vitaliy_Kiselev

@Alfi666

To measure velocity sensing you don't need anything except two contacts. You just need to remember definition of velocity.

Alfi666

@Vitaliy_Kiselev well.. from 2 contacts... how do they know if I pressed it hard or just softly? :) .. or do they use the carbon rubber thing which is changing its resistance? :)

Vitaliy_Kiselev

Velocity is velocity. It is not pressure.

Thing you are talking is called aftertouch. Normally on all modern keyboards it is channel (for all keys) and use something like piezo crystal.

Alfi666

Well OK, in MIDI editor, I see this as velocity (ie. the speed of how fast you press the key)... but if you press it fast, it will end up with stronger pressure (impact) as well.... and like on real piano, it is a different sound.

I found this on one forum:

"Velocity is how hard you strike the key. Hit it softly the volume is less. Strike it hard the volume is more. Velocity can be programmed to control other parameters as well. With your guitar sound the velocity likely opens up a filter to make it brighter and twangier.

Aftertouch is when you've already struck the key and still depressed down you can apply more pressure to the key and have it control a variety of effects or parameters. An organ sound may use aftertouch to increase or enable a rotary speaker effect. Saxophone maybe add some growl to it when the key is pushed harder. Vibrato to strings."

So I meant Velocity :) .. I wasn't even aware about aftertouch (don't have it on my old Roland).

Thanks anyway :)

Vitaliy_Kiselev

You clearly need to go back and check that velocity is.

Physical meaning and definition.

As key, generally, has one degree of freedom, it is just dx/dt (displacement/time spend on this).

So, if you know the moment then initial contact had been off and know the moment of second contact coming on, you can calculate velocity.

If you search, I am sure that you'll find description on how exactly they are doing this on modern keybeds.

Vitaliy_Kiselev

In fact, most important in the first post is one thing.

How proper programming and optimization allow cheap and slow Atom processor to handle all the load, including very good wavetable synth and also physical modelling and analog synth parts.

Make it in tablet form with USB port for input for master keyboard and digital and headphone outputs and you are done.

Alfi666

Ah thanks ! Now I got it... so they calculate the time between I push the key (releas an SPST), until I reach the "bottom" (push an SPST)... if its fast, it means it is being pressed hardly :)

I was thinking about potentiometers, but that wouldn't be very reliable.

Thanks! :)

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