dsp.AllpassFilter coefficient translation

Hi

I need to create an All Pass filter with selectable frequency in an audio plugin I´m developing. As Frequency is not a property in dsp.AllpassFilter object, is there any function to calculate the coefficientes matrix from frequency input (among other parameters of course)? (e.g something similar to designShelvingEQ or designVarislopeFilter).

If not, any formulas to buitl my own function?

Thanks

Br

Pablo

[Pablo Panitta]

I´ve found the answer in the description of dfilt.allpass function, where the transfer function of all pass filter is shown (just in case someone else is interesting in this)

Answer 1

[jibrahim]

Relevant methods of dsp.allpassFilter include:

• freqz: Frequency response of discrete-time filter System object
• coeffs: Returns the filter System object coefficients in a structure

[Pablo Panitta]

Thanks jibrahim for your promt response, but I don´t see how this two methods can help me. freqz is for visualization analysis and coeff is to know the coefficients of a filter. I need to calculate the coefficients from a know frequency cutoff value (selectable by user).

[jibrahim]

I see, sorry about the confusion. Can you say more about the cutoff frequency of the all-pass filter? Is this a crossover filter?

[Pablo Panitta]

Yes of course jibrahim, the frecuency where we have a phase shift of n*pi/2 [rad] (n=order). e.g In a second order ap filter would be phase shift of pi [rad].