PitchTimeAmdf

computes the lag of the average magnitude difference function
> called by ::ComputePitch
>
> @param x: audio signal
> @param iBlockLength: block length in samples
> @param iHopLength: hop length in samples
> @param f_s: sample rate of audio data 
>
> @retval f_0 amdf lag (in Hz)
> @retval t time stamp of f_0 estimate (in s)
 ======================================================================

0001 %computes the lag of the average magnitude difference function
0002 %> called by ::ComputePitch
0003 %>
0004 %> @param x: audio signal
0005 %> @param iBlockLength: block length in samples
0006 %> @param iHopLength: hop length in samples
0007 %> @param f_s: sample rate of audio data
0008 %>
0009 %> @retval f_0 amdf lag (in Hz)
0010 %> @retval t time stamp of f_0 estimate (in s)
0011 % ======================================================================
0012 function [f_0, t] = PitchTimeAmdf(x, iBlockLength, iHopLength, f_s)
0013 
0014     % blocking
0015     [x_b, t] = ToolBlockAudio(x, iBlockLength, iHopLength, f_s);
0016     iNumOfBlocks = size(x_b, 1);
0017     
0018     % allocate memory
0019     f_0 = zeros(1, iNumOfBlocks);
0020 
0021     % initialization
0022     f_max = 2000;
0023     f_min = 50;
0024     eta_min = round(f_s/f_max);
0025     eta_max = round(f_s/f_min);
0026 
0027     for n = 1:iNumOfBlocks
0028   
0029         if (sum(abs(x_b(n, :))) == 0)
0030             f_0(n) = 0;
0031             continue;
0032         end
0033         
0034         % calculate the amdf_I minimum
0035         afAMDF = amdf_I(x_b(n, :), eta_max);
0036         [fDummy, T_0(n)] = min(afAMDF(1+eta_min:end));
0037         
0038         % convert to Hz
0039         f_0(n) = f_s ./ (T_0(n) + eta_min);
0040     end
0041 end
0042 
0043 function [AMDF] = amdf_I(x, eta_max)
0044     K = length(x);
0045  
0046     AMDF = ones(1, K);
0047     
0048     for eta=0:min(K-1,eta_max-1)
0049         AMDF(eta+1) = sum(abs(x(1:K-1-eta) - x(eta+2:end))) / K;
0050     end
0051 end