Added ICS-43432 equalizer filter

esp32-i2s-slm.ino

@@ -95,6 +95,12 @@ const float ICS43434_B[] = {0.47733, -0.48649, -0.33646, 0.23462, 0.11102};
 const float ICS43434_A[] = {1.0, -1.9307338, 0.8651946, 0.0644284, 0.0011125};
 IIRFilter ICS43434(ICS43434_B, ICS43434_A);
 
+// TDK/InvenSense ICS-43432
+// Datasheet: https://www.invensense.com/wp-content/uploads/2015/02/ICS-43432-data-sheet-v1.3.pdf
+const float ICS43432_B[] = {-0.457337, 1.1222867, -0.77818279, 0.0096893, 0.1034567};
+const float ICS43432_A[] = {1,-3.3420781, 4.4033694, -3.0167073, 1.2265537, -0.2962229, 0.0251086};
+IIRFilter ICS43432(ICS43432_B, ICS43432_A);
+
 // TDK/InvenSense INMP441
 // Datasheet: https://www.invensense.com/wp-content/uploads/2015/02/INMP441.pdf
 const float INMP441_B[] = {1.00198, -1.99085, 0.98892};

ics43432.m

@@ -0,0 +1,59 @@
+%
+% ICS-43432 Equalizer filter design
+%
+% (c)2019 Ivan Kostoski
+%
+
+clear;
+Fs = 48000;
+format long G;
+
+% IEC specified frequencies
+iec_w = [10, 12.5, 16, 20, 25, 31.5, 40, 50, 63, 80, ...
+         100, 125, 160, 200, 250, 315, 400, 500, 630, 800, ...
+         1000, 1250, 1600, 2000, 2500, 3150, 4000, 5000, 6300, 8000, ...
+         10000, 12500, 16000, 20000];
+
+% Values visually estimated from ICS-43432 datasheet for IEC frequencies
+% https://www.invensense.com/wp-content/uploads/2015/02/ICS-43432-data-sheet-v1.3.pdf
+% Figure 5 on page 9
+%            10, 12.5,   16,   20,   25,  31.5,   40,   50,   63,   80,
+ds_e_dB = [ -22,  -19,  -15,  -12,   -8,    -6, -4.5, -3.5, -2.1, -1.1, ...
+           -0.4, +0.1, +0.6, +0.9, +1.0,   0.9, +0.8, +0.6, +0.4, +0.3, ...
+              0, +0.3,  +0.4, +0.5, +0.7, +1.0, +1.2, +1.4, +1.8, +2.3, ...
+           +3.5, +6.0,  +9.0, +14.0];
+
+% Manually chosen and adjusted values for fitting the transfer function
+ds_f  = [ 20, 100,   630, 1150, 2000, 10000, 20000];
+ds_dB = [-16, -0.5, +0.7,    0, +0.5,  +3.5,   +14];
+[ds_B, ds_A] = invfreqz(arrayfun(@db2mag, ds_dB), (ds_f.*((2*pi)/Fs)), 6, 4);
+% Stabilize polynoms
+ds_Bs = polystab(ds_B) * norm(ds_B) / norm(polystab(ds_B));
+ds_As = polystab(ds_A) * norm(ds_A) / norm(polystab(ds_A));
+ds_H = freqz(ds_Bs, ds_As, iec_w, Fs);
+
+% Equalizer filter, i.e. inverse from estimated transfer filter
+% Swap A and B coefficients, and normalize to ds_B(1) 
+eq_B = ds_As./ds_Bs(1)
+eq_A = ds_Bs./ds_Bs(1)
+eq_H = freqz(eq_B, eq_A, iec_w, Fs);
+% Check for poles ouside unit circle
+roots(eq_B)
+roots(eq_A)
+
+clf;
+hold on;
+semilogx(iec_w, ds_e_dB, 'g;ICS-43432 Datasheet plot (estimated);');
+semilogx(iec_w, 20 * log10 (abs (ds_H)), 'r;IIR filter frequency response;');
+semilogx(iec_w, (ds_e_dB + 20*log10(abs(eq_H))), 'b;Adjusted frequency response;', 'linewidth', 3);
+title("ICS-43432 Adjusted frequency response");
+grid minor;
+xlabel('Frequency (Hz)');
+xlim([10, 20000]);
+ylabel('Amplitude (dB)');
+ylim([-20, 20]);
+legend ('boxoff');
+legend ('location', 'northwest');
+ylim ([-20, 20]);
+grid on;
+hold off;