[PD] [bp~] really equal to [vcf~]?

[Claude Heiland-Allen]

On 25/07/14 14:36, Alexandre Torres Porres wrote:
>> it's accurate to say that [biquad~] is a real-valued 2-pole/2-zero filter.
>
> but why, if the poles and zeros can have complex values?

If the poles (zeros) occur in as a complex conjugate pair (with 
identical real parts and opposite imaginary parts), or both poles 
(zeros) are real, then the filter will have real output for real input. 
  Having only real coeffecients for biquad forces the poles (zeros) to 
take this form.


Claude
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