calibration: we want to preserve the sign when transforming filter into minimum phase

calibration/src/sphear_design_fir_filters.m

@@ -96,12 +96,14 @@ function [FIR IR MPS] = sphear_design_fir_filters(F, n, SR, W, X, Y, Z, S, T, U,
     %% https://ccrma.stanford.edu/~jos/filters/Conversion_Minimum_Phase.html
     %%
     MPS(b,:) = real(ifft(mps(fft(IR(b,:)))));
+    %% we need to preserve the sign, the minimum phase transformation strips it
+    sgn = sign(IR(b,round(n/2+1)));
     %%
     %% create a raised cosine window for the end of the IR
     %% to make sure IR decays to zero (last 8 samples of a 256 sample IR)
     end_window = tukeywin(2 * n, 0.025)(n+1:end);
     %% truncate to original size and window end
-    FIR(b,:) = (MPS(b,:)')(1:n) .* end_window;
+    FIR(b,:) = (MPS(b,:)')(1:n) .* end_window * sgn;
   end
 end