Normalize the coefficients to fit in range +-1, so h_fir_max = 1.

applications/apertif/matlab/pfir_coeff.m

@@ -27,7 +27,7 @@
 %   bandwidth BWchan. Typically BWchan = 1/N or somewhat more have -3dB
 %   reponse between channels.
 %
-%   The FIR coeeficients can be caluculated with Matlab 'fir1' or with
+%   The FIR coefficients can be caluculated with Matlab 'fir1' or with
 %   Matlab 'fircls1' dependend on config.design.
 %
 %   For Matlab fircls1() r_pass and r_stop are the maximum passband and
@@ -36,6 +36,12 @@
 %   interpolating a shorter filter with an upsampling factor Q. This
 %   reduces computation time substantially. N, L and Q must be powers of 2.
 %
+%   The FIR coefficients are normalized to fit in range +-1. Given that
+%   the impulse response has a sync pulse shape this implies that the
+%   largest coefficient is h_fir_max = 1. Most energy is passed on via
+%   the center tap and therefore the filter DC gain per poly phase
+%   h_fir_dc_gain is close to 1.
+%
 %   For nof_bits>1, the FIR filter coefficients are quantized with
 %   nof_bits bits.
 %
@@ -114,13 +120,20 @@ else
     end
 end;
 
-% normalization, scale coefficients to have DC response is 1
-h_fir = h_fir / sum(h_fir);
+% normalize the coefficients to fit in range +-1
+disp(sprintf('pfir_coeff : Normalizing the PFIR coefficients to fit in range +-1.'));
+h_fir = h_fir / max(h_fir);
+h_fir_max = max(h_fir);  % note: is 1 due to the normalization
+h_fir_min = min(h_fir);
+h_fir_dc_gain = sum(h_fir) / N;
+disp(sprintf('             . Maximum coefficient value : %f', h_fir_max));
+disp(sprintf('             . Minimum coefficient value : %f', h_fir_min));
+disp(sprintf('             . DC gain per polyphase     : %f\n', h_fir_dc_gain));
 
 % quantize the coeffients
 if nof_bits>0
     disp(sprintf('pfir_coeff : Quantizing FIR coefficients nof_bits = %d\n', nof_bits));
-    h_fir = quantize(h_fir, max(h_fir), nof_bits, 'half_away');
+    h_fir = quantize(h_fir, h_fir_max, nof_bits, 'half_away');  % note: h_fir_max is 1 due to the normalization
 end;
 
 % output FIR coefficient