[sdiy] Question for those with musical ears

Mike Beauchamp list at mikebeauchamp.com
Fri Apr 16 18:32:54 CEST 2021

On 4/14/21 7:47 PM, Mike Bryant wrote:
> Consider a continuous glissando played on an analogue synth - the frequency rises smoothly between the start and end pitches.
> But on a digital synth there will always be discrete steps between successive frequencies as the frequency is gradually stepped between the start and end pitches.
> Question is, what is the minimum step (in cents) needed such that the best musical ears cannot tell the frequency isn't rising smoothly as on the analogue synth, but in many discrete steps.
> It may be that the rate of change can effect it so if so please assume a glissando starting at middle C rising at 1 second per semitone.
> Thanks
> Mike

Interesting question Mike..

I have built a continuous pitch instrument that covers 4 octaves, while 
it is all analog it also has a MIDI output. So those 4 octaves get 
turned into a 14bit pitch bend message which should be .2 cent 
resolution. Previously I was only getting 12 useable bits out of my ADC 
which is a little more than 1-cent resolution and that's as low of 
resolution as I'm personally OK with going.

It would be very easy to test the perception of this by just lowering 
the ADC resolution until I hear some stair stepping in the pitch. But 
like all the other perceptions, I'm very reluctant to assume that my 
threshold is on par with other people that might use this gear. If 
you've ever heard me sing, you know that pitch isn't something I'm most 
sensitive to :)

But as others have mentioned as well, the context probably matters - so 
if another instrument is holding a steady note while this one is being 
changed or if there are long reverb tails or delays to leave the 
original note for the new note to beat against then the perceptions of 
the pitch changes would be heard in these beatings and that could make 
things very noticeable.

I'd imagine this gets more sensitive at higher pitches too:

- A 1 cent pitch difference at C2 gives a beat frequency of .5Hz. Great.
- A 1 cent pitch difference at C8 gives a beat frequency of 41Hz. Yikes!

When it comes to turning something into discrete steps, I think we 
should be aiming for close-to-ideal instead of barely-perceptible when 
hardware allows.

The pitch resolution is usually an after-thought since most synths are 
played with keyboards, so the pitch resolution is only important for the 
tuning granularity and pitch-bend-wheel flourishes. But more alternative 
controllers are around that are pushing for constant continuous pitch 
(like the giant Roli) and I think digital synths need to be designed 
with this in mind, allowing for large pitch-bends (at least 4 octaves) 
and with a very high resolution.


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