Semester assignment for the course "Multimedia systems and virtual reality" of THMMY in AUTH university.
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function frameT = iFilterbank(frameF, frameType, winType)
%Implementation of the Inverse Filter Bank step
% Usage frameT = iFilterbank(frameF, frameType, winType), where:
% Inputs
% - frameF is the frame in the frequency domain, in MDCT coefficients
% representation containing both channels of the audio stored in an
% array of dimensions 1024X2
% - frameType is the type of the current frame in string
% representation, can be one of "OLS" (ONLY_LONG_SEQUENCE), "LSS"
% (LONG_START_SEQUENCE), "ESH" (EIGHT_SHORT_SEQUENCE), "LPS"
% (LONG_STOP_SEQUENCE)
% - winType is the type of the window selected, can be one of "KBD",
% "SIN"
%
% Output
% - frameT is a frame in the time domain, containing both channels of
% the audio stored in an array of dimensions 2048X2
% Declares persistent windows variables and initializes if empty
persistent kaiserWindowLong kaiserWindowShort sinWindowLong sinWindowShort;
if isempty(kaiserWindowLong) || isempty(kaiserWindowShort) || ...
isempty(sinWindowLong) || isempty(sinWindowShort)
kaiserLong = kaiser(1024, 6*pi);
kaiserSumLong = sum(kaiserLong);
kaiserShort = kaiser(128, 4*pi);
kaiserSumShort = sum(kaiserShort);
for n = 1:1024
kaiserWindowLong(n) = sqrt(sum(kaiserLong(1:n))/kaiserSumLong);
kaiserWindowLong(1024 + n) = sqrt(sum(kaiserLong(1:end-n+1))/kaiserSumLong);
sinWindowLong(n) = sin(pi*(n + 0.5)/2048);
sinWindowLong(1024 + n) = sin(pi*(1024 + n + 0.5)/2048);
end
for n = 1:128
kaiserWindowShort(n) = sqrt(sum(kaiserShort(1:n))/kaiserSumShort);
kaiserWindowShort(128 + n) = sqrt(sum(kaiserShort(1:end-n+1))/kaiserSumShort);
sinWindowShort(n) = sin(pi*(n + 0.5)/256);
sinWindowShort(128 + n) = sin(pi*(128 + n + 0.5)/256);
end
end
frameT(2048, 2) = 0;
% Applies appropriate window to the frame
for channel=1:2
if strcmp(frameType, 'OLS')
frameT = imdct4(frameF);
if strcmp(winType, 'KBD')
frameT(:, channel) = frameT(:, channel) .* kaiserWindowLong(:);
elseif strcmp(winType, 'SIN')
frameT(:, channel) = frameT(:, channel) .* sinWindowLong(:);
else
error('filterbank, l[20]: Unsupported window type input!')
end
elseif strcmp(frameType, 'LSS')
frameT = imdct4(frameF);
if strcmp(winType, 'KBD')
frameT(1:1024, channel) = frameT(1:1024, channel) .* kaiserWindowLong(1:1024)';
frameT(1473:1600, channel) = frameT(1473:1600, channel) .* kaiserWindowShort(129:end)';
frameT(1601:end, channel) = 0;
elseif strcmp(winType, 'SIN')
frameT(1:1024, channel) = frameT(1:1024, channel) .* sinWindowLong(1:1024)';
frameT(1473:1600, channel) = frameT(1473:1600, channel) .* sinWindowShort(129:end)';
frameT(1601:end, channel) = 0;
else
error('filterbank, l[20]: Unsupported window type input!')
end
elseif strcmp(frameType, 'LPS')
frameT = imdct4(frameF);
if strcmp(winType, 'KBD')
frameT(1:448, channel) = 0;
frameT(449:576, channel) = frameT(449:576, channel) .* kaiserWindowShort(1:128)';
frameT(1025:end, channel) = frameT(1025:end, channel) .* kaiserWindowLong(1025:end)';
elseif strcmp(winType, 'SIN')
frameT(1:448, channel) = 0;
frameT(449:576, channel) = frameT(449:576, channel) .* sinWindowShort(1:128)';
frameT(1025:end, channel) = frameT(1025:end, channel) .* sinWindowLong(1025:end)';
else
error('filterbank, l[20]: Unsupported window type input!')
end
elseif strcmp(frameType, 'ESH')
for subFrameIndex = 1:8
subFrame = imdct4(frameF((subFrameIndex - 1) * 128 + 1:subFrameIndex * 128, channel));
if strcmp(winType, 'KBD')
subFrame = subFrame .* kaiserWindowShort';
elseif strcmp(winType, 'SIN')
subFrame = subFrame .* sinWindowShort';
end
frameT(449 + (subFrameIndex - 1) * 128 + 1:449 + (subFrameIndex + 1) * 128) = ...
frameT(449 + (subFrameIndex - 1) * 128 + 1:449 + (subFrameIndex + 1) * 128) + subFrame';
end
end
end
end