Листинг myVAD.m

function trimmedX = myVAD(x)

% Syntax: trimmedSample = myVAD(samplex);

% This function accepts an audio sample 'samplex' as input and returns a

% trimmed down version with non-speech sections trimmed off. Also known as

% voice activity detection, it utilises the algorithm due to Rabiner &

% Sambur (1975)

Ini = 0.1; % Initial silence duration in seconds

Ts = 0.01; % Frame width in seconds

Tsh = 0.005; % Frame shift in seconds

Fs = 16000; % Sampling Frequency

counter1 = 0;

counter2 = 0;

counter3 = 0;

counter4 = 0;

ZCRCountf = 0; % Stores forward count of crossing rate > IZCT

ZCRCountb = 0; % As above, for backward count

ZTh = 40; % Zero crossing comparison rate for threshold

w_sam = fix(Ts*Fs); % No of Samples/window

o_sam = fix(Tsh*Fs); % No of samples/overlap

lengthX = length(x);

segs = fix((lengthX-w_sam)/o_sam)+1; % Number of segments in speech signal

sil = fix((Ini-Ts)/Tsh)+1; % Number of segments in silent period

win = hamming(w_sam);

Limit = o_sam*(segs-1)+1; % Start index of last segment

FrmIndex = 1:o_sam:Limit; % Vector containing starting index for each segment

ZCR_Vector = zeros(1,segs); % Vector to hold zero crossing rate for all segments

% Below code computes and returns zero crossing rates for all segments in

% speech sample

for t = 1:segs

ZCRCounter = 0;

nextIndex = (t-1)*o_sam+1;

for r = nextIndex+1:(nextIndex+w_sam-1)

if (x(r) >= 0) && (x(r-1) >= 0)

elseif (x(r) >= 0) && (x(r-1) < 0)

ZCRCounter = ZCRCounter + 1;

elseif (x(r) < 0) && (x(r-1) < 0)

elseif (x(r) < 0) && (x(r-1) >= 0)

ZCRCounter = ZCRCounter + 1;

end

end

ZCR_Vector(t) = ZCRCounter;

end

% Below code computes and returns frame energy for all segments in speech

% sample

Erg_Vector = zeros(1,segs);

for u = 1:segs

nextIndex = (u-1)*o_sam+1;

Energy = x(nextIndex:nextIndex+w_sam-1).*win;

Erg_Vector(u) = sum(abs(Energy));

end

IMN = mean(Erg_Vector(1:sil)); % Mean silence energy (noise energy)

IMX = max(Erg_Vector); % Maximum energy for entire utterance

I1 = 0.03 * (IMX-IMN) + IMN; % I1 & I2 are Initial thresholds

I2 = 4 * IMN;

ITL = min(I1,I2); % Lower energy threshold

ITU = 5 * ITL; % Upper energy threshold

IZC = mean(ZCR_Vector(1:sil)); % mean zero crossing rate for silence region

stdev = std(ZCR_Vector(1:sil)); % standard deviation of crossing rate for

% silence region

IZCT = min(ZTh,IZC+2*stdev); % Zero crossing rate threshold

indexi = zeros(1,lengthX); % Four single-row vectors are created

indexj = indexi; % in these lines to facilitate computation below

indexk = indexi;

indexl = indexi;

% Search forward for frame with energy greater than ITU

for i = 1:length(Erg_Vector)

if (Erg_Vector(i) > ITU)

counter1 = counter1 + 1;

indexi(counter1) = i;

end

end

ITUs = indexi(1);

% Search further forward for frame with energy greater than ITL

for j = ITUs:-1:1

if (Erg_Vector(j) < ITL)

counter2 = counter2 + 1;

indexj(counter2) = j;

end

end

start = indexj(1)+1;

Erg_Vectorf = fliplr(Erg_Vector);% Flips round the energy vector

% Search forward for frame with energy greater than ITU

% This is equivalent to searching backward from last sample for energy > ITU

for k = 1:length(Erg_Vectorf)

if (Erg_Vectorf(k) > ITU)

counter3 = counter3 + 1;

indexk(counter3) = k;

end

end

ITUf = indexk(1);

% Search further forward for frame with energy greater than ITL

for l = ITUf:-1:1

if (Erg_Vectorf(l) < ITL)

counter4 = counter4 + 1;

indexl(counter4) = l;

end

end

finish = length(Erg_Vector)-indexl(1)+1;% Tentative finish index

% Search back from start index for crossing rates higher than IZCT

BackSearch = min(start,25);

for m = start:-1:start-BackSearch+1

rate = ZCR_Vector(m);

if rate > IZCT

ZCRCountb = ZCRCountb + 1;

realstart = m;

end

end

if ZCRCountb > 3

start = realstart; % If IZCT is exceeded in more than 3 frames

% set start to last index where IZCT is exceeded

end

% Search forward from finish index for crossing rates higher than IZCT

FwdSearch = min(length(Erg_Vector)-finish,25);

for n = finish+1:finish+FwdSearch

rate = ZCR_Vector(n);

if rate > IZCT

ZCRCountf = ZCRCountf + 1;

realfinish = n;

end

end

if ZCRCountf > 3

finish = realfinish; % If IZCT is exceeded in more than 3 frames

% set finish to last index where IZCT is exceeded

end

x_start = FrmIndex(start); % actual sample index for frame 'start'

x_finish = FrmIndex(finish-1); % actual sample index for frame 'finish'

trimmedX = x(x_start:x_finish); %T rim speech sample by start and finish indices

Дата добавления: 2015-07-11