[sdiy] TB303 Slide

Richie Burnett rburnett at richieburnett.co.uk
Sun Jun 10 21:33:31 CEST 2012


Tom Wiltshire wrote:

> Could we just say "RC glide"?
> It's simple, descriptive, and it leaves to one side the question of 
> whether it's constant time or not!!

"First-order RC lag" with fixed time-constant of approx 22ms.  (Exact TC 
varies slightly from unit to unit with the tolerance on C35.)

When sliding from an old note to a new note the oscillator CV follows this 
equation:

Vpresent = Vnew + (Vold - Vnew) * exp(-t / 0.022)

where Vnew is the new note's CV, Vold is the old note's CV, t is the time in 
seconds since the slide was invoked, and Vpresent is the instantaneous pitch 
CV.

The start of the slide process is always audible because the sequencer holds 
on the gate from the currently playing note then the pitch CV starts slewing 
towards the pitch of the new note.  How much of the end of the slide process 
you hear depends on how long the second note is programmed to be.  If you 
slide to a 16th note at a brisk tempo you might not hear it get anywhere 
near the destination pitch before the note is snuffed out by the gate line 
dropping low.  Arbitrarily extending the programmed length of the second 
note will easily allow you to hear as much of the slide as you want.

-Richie, 




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