MATLAB: Help on understanding Band Properties of Arbitrary Response Filter in FilterBuilder

arbitraryfilterfilterbuildervector

hello all,

I would like your help to understand the inputs of Frequencies and Amplitudes, of the Band Properties Panel.

So I open filterbuilder, select the Arbitrary Response Filter. In the Main tab I set Impulse Response to FIR, Order of 200 and Filter Type Single-rate. In the Response Specifications the number of bands is 1, I have specified the response as Amplitudes and the Frequency units are set to Hz. I set the Input Fs equal to 44100Hz.

In the Band Properties, the Frequencies vector acts as the X axis while the Amplitudes as the Y?

I guess what I'm asking is what do the vectors Frequencies and Amplitudes serve as?

Thank you in advance!

Best Answer

You can think of Frequency and Amplitude as samples from frequency response of the filter. If you plot Amplitude vs. Frequency, it should approximately look like your desired frequency response.

HTH

Related Solutions

MATLAB: Arbitrary response Filterbuilder Amplitude question

Tony, You're incorrect about the frequency vector, it must begin at 0 and end with Fs/2

I've shown you already how to convert dB SPL to amplitudes:

dB = [108.8 108.8 104.5  111.4  116.2  116.5  114.7  122.4  130.8...
127.2  133.4  129.6  137.2  136.0  137.5  136.6  136.2...
134.0  135.0  133.7  133.8  133.1  132.6  131.8  131.9...
132.3  131.2  131.6  131.6  132.9  131.4  127.6  124.1  125.2];
A = sqrt(db2pow(dB));

A is now your amplitude vector. Note that I simply repeated the entry for 12.5 Hz for the necessary 0 frequency value.

Now for your frequency vector, it must begin with 0 and end with Fs/2.

F  = [0 12.500  16.000  20.000  25.000  31.500  40.000  50.000  63.000...
  80.000  100.000  125.000  160.000  200.000  250.000  315.000  400.000...
  500.000  630.000  800.000  1000.00  1250.00  1600.00  2000.00  2500.00...
  3150.00  4000.00  5000.00  6300.00  8000.00  10000.0  12500.0  16000.0  24000.0];

You can paste the F and the A vector into the Workspace and then put those variables F and A in the Arbitrary Response Design dialog, or simply use the code I gave you in my first answer which does exactly what filterbuilder does from the command line.

Thank you for accepting my answer if I have helped you.

If you want you can try to have a first frequency element not equal to 0 and a last element not equal to Fs/2, but it will errror.

MATLAB: Designing an Arbitrary FIR Filter

This is probably as close as you can get:

Frequency = [100  125  160  200  250  315  400  500  630  800  1000  1250  1600  2000  2500  3150  4000  5000  6300  8000  10000];
Required_Filter_Response = [55.38  55.74  52.13  52.64  51.25  49.04  46.50  44.99  42.95  40.73  39.47  37.53  35.36  34.33  32.33  30.36  28.01  25.98  23.19  20.42 18.65];
Fs = 20000;                                                                 % Create Sampling Frequency (Not Supplied, Must Be > 20000 Here)
Fn = Fs/2;
Fnew = linspace(min(Frequency), max(Frequency), fix(numel(Frequency)/2)*2);
Rnew = interp1(Frequency, Required_Filter_Response, Fnew);
b = firls(100, Fnew/Fn, Rnew/max(Rnew));
figure
freqz(b, 1, 2^14, Fs)
[h,f] = freqz(b, 1, 2^14, Fs);
figure
plot(Fnew, 20*log10(Rnew/max(Rnew)))
hold on
plot(f, 20*log10(abs(h)))
hold off

Note that the filter and the desired response are essentially the same in the second plot.

Best Answer

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MATLAB: Arbitrary response Filterbuilder Amplitude question

MATLAB: Designing an Arbitrary FIR Filter

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