[sdiy] harmonics & vibrato

[jhaible at debitel.net]

Very good points.

Randomizing Vibrato is a good start (The Yamaha VL7 has this), but I think
it's not enough. 

"Random" functions are much overused / misused in music, IMO.

Randomize the pitch of individual notes on a (DCO or VA) Polysynth?
As if the voice allocation of a polysynth would work like random!

Randomize the quantisation of drum machines to get a human touch ?
As if a good drummer would play around the beat at random!

(sorry for the rant.)

Back to vibrato, I think what we need is a good control of the player
on both, vibrato depth and vibrato rate. Routing both, vibrato depth
and a tiny amount of vibrato speed to aftertouch is helpful. But
vibrato depth and speed being linked too much isn't perfect either.

Initial vibrato amount on a mod wheel, and then additional depth and 
rate on Aftertouch might be better.

Another thing to experiment: LFO with DC offset, depth (including the
offset part) thru a VCA, controlled by Aftertouch, and then AC-coupled
before it goes to the VCO. Thus a rather slowly varying force from
your fingertips will be superposed to the LFO's wave.

JH.






> Like vibrato. Firstly real vibrato isn't a sine wave. It's going to be 
> slightly randomised wrt both pitch and amplitude. And it probably won't be 
> perfectly symmetric. And it will have a frequency curve that varies. Listen 
> to a real cellist and you can hear that their vibrato often starts slow and 
> then speeds up a little.
> 
> Secondly I'm wondering how the speed of a moving finger compares with the 
> speed of the displacement waves in a string that create the sound. If 
> they're comparable, you're going to get harmonic non-linearities because 
> the nodes won't have time to settle the way they would if a fixed obstacle 
> were damping the string.
> 
> Bottom line is you'll get interesting timbral variations that are richer 
> than just a generic fixed LFO wobble. If I had a frequency shifter to hand 
> (which I don't) I'd wonder about creating string vibrato with a slightly 
> randomised LFO driving the frequency shift amount as well as VCO frequency.
> 
> If anyone does have one to hand, I'd be interested to hear how the results 
> compare with simple vibrato.
> 
> Richard
> 
> 
> 
> 




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