[sdiy] Question for those with musical ears

Mike Bryant mbryant at futurehorizons.com
Fri Apr 16 18:54:19 CEST 2021

Thanks Mike

Good point about C2 vs C8.  Need to think on this one.  I could use '0.n' Hz bins rather than 'n' cent bins, but would end up with an awful lot of bins to check at higher frequencies.


-----Original Message-----
From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Mike Beauchamp
Sent: 16 April 2021 17:33
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] Question for those with musical ears

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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