fit the spline only for the high frequencies, for low frequencies keep the A2B coefficients untouched, make graphs of filters better

sphear_fir_design.m

@@ -11,12 +11,12 @@
 %% n: order of the FIR filter being created
 %% maxboost: max high and low frequency boost in dB of the final filter
 %% Fs: sampling rate
+%% Fl: frequency limit, below it use A2B matrixes, above it use WXYZ shapes
 %%
-%% for the first run do not supply Fl/W/XYZ, render the filters and from inspection
-%% determine the limit frequency, then run sphear_fir_extract to extract the
-%% W and XYZ filter shapes and run this again with the extra parameters below
+%% for the first run do not supply W/XYZ, render the filters and then run
+%% sphear_fir_extract to extract the W and XYZ filter shapes, finally run
+%% this again with the extra parameters below
 %%
-%% Fl: frequency limit, below it use A2B matrixes, above it use WXYZ shapes
 %% W: extracted shape of W filter (used above Fl)
 %% XYZ: extracted shape of X, Y and Z filters (used above Fl)
 %%
@@ -38,8 +38,6 @@
 
 function [FIR] = sphear_fir_design(F, A2BF, n, maxboost, Fs, Fl, W, XYZ)
 
-  FIR = zeros(4, 4, (n + 1));
-
   %% all b format components
   for b = 1:4
     %% all capsules
@@ -75,10 +73,19 @@ function [FIR] = sphear_fir_design(F, A2BF, n, maxboost, Fs, Fl, W, XYZ)
 	end
       end
 
-      %% fit a spline over the existing points and extrapolate
-      %% for low and high ends of spectrum
-      fi = (0:200/(Fs/2):1)';
-      ri = spline(F/(Fs/2), A2BF(:,c,b)', fi);
+      %% fit a spline to the W and XYZ segments and extrapolate
+      %% highest frequency if it does not exist in the measurements
+      fh = (F(dlast)/(Fs/2):200/(Fs/2):1)';
+      fh(end) = 1;
+      rh = spline(F(dlast:end)/(Fs/2), A2BF(dlast:end,c,b)', fh);
+
+      %% extract the low frequency A2B coefficients
+      fl = [0 F(1:dlast-1)']' ./ (Fs/2);
+      rl = [A2BF(1,c,b) A2BF(1:dlast-1,c,b)']';
+
+      %% concatenate low and high frequency arrays
+      fi = cat(1, fl, fh);
+      ri = cat(1, rl, rh);
 
       printf("low frequency boost %f, high frequency boost %f\n", 20*log10(ri(1)), 20*log10(ri(end)));
       %% force a max boost at low and high frequencies
@@ -95,18 +102,20 @@ function [FIR] = sphear_fir_design(F, A2BF, n, maxboost, Fs, Fl, W, XYZ)
 	end
       end
       
-      %% real measured points
+      %% plot real measured points
+      axis([300, 24000]);
+      grid on;
       if (b == 1)
-	semilogx(F/(Fs/2), A2BF(:,c,b)','*g');
+	semilogx(F, 20*log10(abs(A2BF(:,c,b)))','*k');
       else
-	semilogx(F/(Fs/2), A2BF(:,c,b)','*b');
+	semilogx(F, 20*log10(abs(A2BF(:,c,b)))','*k');
       end
       hold on;
-      %% extrapolated spline
+      %% plot extrapolated spline
       if (b == 1)
-	semilogx(fi,ri,'g');
+	semilogx(fi*(Fs/2), 20*log10(abs(ri)), 'b');
       else
-	semilogx(fi,ri,'r');
+	semilogx(fi*(Fs/2), 20*log10(abs(ri)), 'r');
       end
 
       %% design the filter