原理参考：

http://www.mahong.me/archives/97

将音频分段，各个段分别使用hrtf在Ls, L, R, Ls, Rrs, Lrs位置处的filter系数。是声音听起来来自Ls, L, R, Rs, Rrs, Lrs，就有旋转效果。

hrtf = load("E:\CIPIC_hrtf_database\standard_hrir_database\subject_21\hrir_final.mat");

Ls = [1 9];

L = [8 9];

R= [17 9];

Rs = [25 9];

Rrs = [17 41];

Lrs = [8 41];

%source from 5.1 to L ch

h_l_l = squeeze(hrtf.hrir_l(L(1), L(2), :));

h_r_l = squeeze(hrtf.hrir_l(R(1), R(2), :));

h_ls_l = squeeze(hrtf.hrir_l(Ls(1), Ls(2), :));

h_rs_l = squeeze(hrtf.hrir_l(Rs(1), Rs(2), :));

h_lrs_l = squeeze(hrtf.hrir_l(Lrs(1), Lrs(2), :));

h_rrs_l = squeeze(hrtf.hrir_l(Rrs(1), Rrs(2), :));

%source from 5.1 to R ch

h_l_r = squeeze(hrtf.hrir_r(L(1), L(2), :));

h_r_r = squeeze(hrtf.hrir_r(R(1), R(2), :));

h_ls_r = squeeze(hrtf.hrir_r(Ls(1), Ls(2), :));

h_rs_r = squeeze(hrtf.hrir_r(Rs(1), Rs(2), :));

h_lrs_r = squeeze(hrtf.hrir_r(Lrs(1), Lrs(2), :));

h_rrs_r = squeeze(hrtf.hrir_r(Rrs(1), Rrs(2), :));

[input, fs] = wavread('input.wav');

h_l = zeros(length(h_l_l), 6);

h_l(:, 1) = h_ls_l;

h_l(:, 2) = h_l_l;

h_l(:, 3) = h_r_l;

h_l(:, 4) = h_rs_l;

h_l(:, 5) = h_rrs_l;

h_l(:, 6) = h_lrs_l;

h_r = zeros(length(h_l_r), 6);

h_r(:, 1) = h_ls_r;

h_r(:, 2) = h_l_r;

h_r(:, 3) = h_r_r;

h_r(:, 4) = h_rs_r;

h_r(:, 5) = h_rrs_r;

h_r(:, 6) = h_lrs_r;

idx = 0;

%change to another direction every 2 second (every N samples)

N = fs * 2;

%divide audio to loop segment, each segment has N samples

loop = int32(length(input(:, 1)) / N);

fadeSize = 1024;

win = hamming(fadeSize * 2, 'symmetric');

fadeIn = win(1: fadeSize, 1);

fadeOut = win(fadeSize + 1 : fadeSize * 2, 1);

y = zeros(length(input(:, 1)), 2);

fadeInData = zeros(fadeSize, loop-1, 2);

fadeOutData = zeros(fadeSize, loop-1, 2);

fadeOutStartIdx = N - fadeSize;

outputStartIdx = 1;

for i = 1:1:loop-1

　　idx = mod(i, 6);

　　if idx == 0

　　　　idx = 6;　　

　　end

　　%current segment is inputStartIdx ~inputEndIdx

　　inputStartIdx = int32((i-1) * N + 1);

　　inputEndIdx = int32(i * N);

　　pInput = pOutput = zeros(N, 2);

　　pInput(:, 1) = input(inputStartIdx : inputEndIdx, 1);

　　pInput(:, 2) = input(inputStartIdx : inputEndIdx, 2);

　　if i * N < length(input(:, 1))

　　　　%current segment filter with HRTF, which make the sound comes from direction idx.

　　　　pOutput(:, 1) = filter(h_l(:, idx), 1, pInput(:, 1));

　　　　pOutput(:, 2) = filter(h_l(:, idx), 1, pInput(:, 2));

　　end

　　%fadeIn fadeOut at the begine & end of current segment to avoid pop noise

　　fadeInData(: ,i, 1) = pOutput(1: fadeSize, 1) .* fadeIn;

　　fadeInData(: ,i, 2) = pOutput(1: fadeSize, 2) .* fadeIn;

　　fadeOutData(: ,i, 1) = pOutput(fadeOutStartIdx + 1: N, 1) .* fadeOut;

　　fadeOutData(: ,i, 2) = pOutput(fadeOutStartIdx + 1: N, 2) .* fadeOut;

　　if i > 1

　　　　%add the cross fade data at the begin & end of segment

　　　　y(outputStartIdx:outputStartIdx + fadeSize-1, 1) = fadeInData(:, i, 1) + fadeOutData(:, i-1, 1);

　　　　y(outputStartIdx:outputStartIdx + fadeSize-1, 2) = fadeInData(:, i, 2) + fadeOutData(:, i-1, 2);

　　else

　　　　%the first segment

　　　　y(outputStartIdx:outputStartIdx + fadeSize-1, 1) = fadeInData(:, i, 1) ;

　　　　y(outputStartIdx:outputStartIdx + fadeSize-1, 2) = fadeInData(:, i, 2) ;

　　end

　　y(outputStartIdx + fadeSize + 1: outputStartIdx + fadeOutStartIdx , 1) = pOutput(fadeSize+1: fadeOutStartIdx, 1);

　　y(outputStartIdx + fadeSize + 1: outputStartIdx + fadeOutStartIdx , 2) = pOutput(fadeSize+1: fadeOutStartIdx, 2);

　　outputStartIdx = outputStartIdx + fadeOutStartIdx; 

end

% low pass filter to avoid pop noise at the begin & end of segment

wn = 10000 / fs;

[B, A] = butter(8, wn, 'low');

y = filter[B, A, y]

wavwrite(y, fs, 'output.wav');