[sdiy] Different pole notches and phasers
raphschwarz at gmail.com
Mon Apr 13 14:14:36 CEST 2020
> Le 13 avr. 2020 à 14:14, Schwarz Raphael <raphschwarz at gmail.com> a écrit :
>> Interesting thoughts
>> Additionally, what’s the difference between a notch filter and a notch created with an allpass filter and the input added together? Is there a difference?
> To me a notch filter removes a narrow frequency band at the cutoff frequency whereas an allpass changes the phase relationship between the input and output and hence creates notches or peaks depending on position when the two are added together. It won’t produce the same result when modulating
>> It seems to me there is, since multiple stages of allpass filters with the input added together (a phaser) creates multiple notches, whereas a multi-pole notch would just be a deeper/narrower notch. Is that right? Or could a 4-pole notch filter have two notches?
> That is more technical but I would assume the number of poles in a notch filter would be like in a bandpass so just steeper. As for a multipole allpass I don’t clearly understand why it creates more than one notch or peak instead of a more important phase displacement . Why two notches at 180° instead of one at 360° or 720° in an 8 pole allpass for example (assuming each cell is 90° )
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