> Having only real coeffecients for biquad forces the poles (zeros) to take this form.

yeah, that makes sense. The tricky part seems to be how a complex conjugate pair does that too. Is it because you'd add them up and then the imaginary part becomes zero? That's what I can think of...

2014-07-25 10:49 GMT-03:00 Claude Heiland-Allen <claude@mathr.co.uk>:

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
--
http://mathr.co.uk

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