[sdiy] Filter cut off DAC

[rburnett at richieburnett.co.uk]

I'd say that the answer is the same as the number of bits required to 
control a VCO :-)  The justification is this....

The human ear isn't particularly sensitive to "brightness" of a sound.  
So you could get away with quite a coarse control over a simple *non 
resonant* low-pass filter.  However, once you increase the resonance, 
you then start to boost a narrow band of frequencies.  Then your ear 
gets much more sensitive to changes in the cutoff frequency.  If you 
take this to the extreme, with enough resonance the filter 
self-oscillates and becomes an oscillator.  The human ear is very 
sensitive to changes in *pitch* though!  So the question now becomes how 
fine a resolution of pitch do I need?

That is how I would think about this problem.  The worst case scenario 
is when the filter is self-oscillating and then "oscillator rules" apply 
in terms of what pitch step size is perceptible.  Maybe something around 
10 cents? ...or as low as 1 cent even?

-Richie,


On 2018-05-21 15:53, paula at synth.net wrote:
> Random question,
> 
> How many bits is "enough" for controlling the filter cut off on a VCF?
> I would start with say 12, but would 16 be better? or 24?
> At some point there's a cost trade off.
> 
> Thoughts?
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