How do I cascade biquad filters (dsp.BiquadFilter)?

Hello everyone,

I want to cascade twelve biquad filters and apply the result to an audio signal.

My problem is that I have twelve frequencies that I want to boost on an audio signal.

My solution would be to use a biquad filter in MATLAB with the dsp.biquad object. I use the designParamEQ function for a parametric equalizer design, so that I'm able to set the gain, bandwidth, filter order and frequency. See the code below from this example.

Fs = 48e3;
N1 = 2;
G  = 5; % 5 dB
Wo = 10000/(Fs/2);
BW = 4000/(Fs/2);
[B1,A1] = designParamEQ(N1,G,Wo,BW);
BQ1 = dsp.BiquadFilter('SOSMatrix',[B1.',[1,A1.']]);

Cascading twelve biquad filters with the dfilt.cascade function does not work. Cascades must be made of discrete-time filter (DFILT) objects and I currently use dsp.BiquadFilter objects.

Is there a way to design a biquad filter with the dsp.BiquadFilter object that is able to boost twelve frequency coefficients? If yes, how do I do this?

By the way, I don't want to change the bandwidth for each frequency. There should be one bandwidth variable and one gain variable with decreasing amplitude for all the frequency coefficients.

How do I apply my biquad filter to an audio signal? Which function should I use?

Is there a better solution than to use a parametric equalizer design?

I can't find any help on this in the MATLAB documentation.

Thanks in advance,

Patrick

Answer 1

[jibrahim]

Hi Patrick,

You can use dsp.FilterCascade to cascade dsp.BiquadFilter objects

[Patrick Boettcher]

Thanks!

However, if I use a filter function MATLAB tells me that there are not enough input arguments. I only have two, the cascaded filter and the signal that I want to apply the filter on. I get the following error message:

% Error using filter
% Not enough input arguments.

% Error in Prototype (line 153)
y = filter(CascadedBiquads,out);

What do I need to change to apply my cascaded biquad filters to a signal?

[jibrahim]

Hi Patrick,

filter is not a supported command for dsp.FIlterCascade.

This is how you should call the object:

y = CascadedBiquads(out);

[Patrick Boettcher]

Thank you for helping me!