[sdiy] VCO autotune for poly analog modular

[Magnus Danielson]

From: Tom Wiltshire <tom at electricdruid.net>
Subject: Re: [sdiy] VCO autotune for poly analog modular
Date: Wed, 4 Apr 2007 15:27:40 +0100
Message-ID: <758F5585-1BDC-4234-AF0F-E34B6A2B1A29 at electricdruid.net>

> 
> On 4 Apr 2007, at 14:38, harrybissell at copper.net wrote:
> 
> > Should be easy to do by calibrating maybe five
> > octave spaced points, then use linear interpolation
> > within those note ranges. The Prophet V worked this way,
> > and it was quite effective. That was a Z-80 iirc with very
> > little RAM
> >
> > H^) harry
> 
> I second that. As others have said, you'd easily manage to do this  
> with a modern uP. Storing a selection of points (octaves are an  
> obvious choice, but you could go to half or quarter-octaves) and  
> doing linear interpolation between them isn't too demanding. To make  
> life easier, you could make sure the chip you use has a hardware  
> multiply, since you'll need to multiply for the interpolation.

The trick is to make a calibration method in which the correction is cheap
and where the calibration may take a few seconds but you generate the
calibration data that makes the correction cheap. You do corrections much more
often than calibration.

Cheers,
Magnus