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103 lines
4.5 KiB
103 lines
4.5 KiB
function frameF = filterbank(frameT, frameType, winType)
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%Implementation of the Filter Bank step
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% Usage frameF = filterbank(frameT, frameType, winType), where:
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% Inputs
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% - frameT is a frame in the time domain, containing both channels of
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% the audio stored in an array of dimensions 2048X2
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% - frameType is the type of the current frame in string
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% representation, can be one of "OLS" (ONLY_LONG_SEQUENCE), "LSS"
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% (LONG_START_SEQUENCE), "ESH" (EIGHT_SHORT_SEQUENCE), "LPS"
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% (LONG_STOP_SEQUENCE)
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% - winType is the type of the window selected, can be one of "KBD",
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% "SIN"
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%
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% Output
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% - frameF is the frame in the frequency domain, in MDCT coefficients
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% representation containing both channels of the audio stored in an
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% array of dimensions 1024X2
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% Declares persistent windows variables and initializes if empty
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persistent kaiserWindowLong kaiserWindowShort sinWindowLong sinWindowShort;
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if isempty(kaiserWindowLong) || isempty(kaiserWindowShort) || ...
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isempty(sinWindowLong) || isempty(sinWindowShort)
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kaiserLong = kaiser(1024, 6*pi);
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kaiserSumLong = sum(kaiserLong);
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kaiserShort = kaiser(128, 4*pi);
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kaiserSumShort = sum(kaiserShort);
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for n = 1:1024
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kaiserWindowLong(n) = sqrt(sum(kaiserLong(1:n))/kaiserSumLong);
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kaiserWindowLong(1024 + n) = sqrt(sum(kaiserLong(1:end-n+1))/kaiserSumLong);
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sinWindowLong(n) = sin(pi*(n + 0.5)/2048);
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sinWindowLong(1024 + n) = sin(pi*(1024 + n + 0.5)/2048);
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end
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for n = 1:128
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kaiserWindowShort(n) = sqrt(sum(kaiserShort(1:n))/kaiserSumShort);
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kaiserWindowShort(128 + n) = sqrt(sum(kaiserShort(1:end-n+1))/kaiserSumShort);
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sinWindowShort(n) = sin(pi*(n + 0.5)/256);
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sinWindowShort(128 + n) = sin(pi*(128 + n + 0.5)/256);
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end
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end
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frameF(1024, 2) = 0;
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% Applies appropriate window to the frame
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for channel=1:2
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if strcmp(frameType, 'OLS')
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if strcmp(winType, 'KBD')
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frameT(:, channel) = frameT(:, channel) .* kaiserWindowLong(:);
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elseif strcmp(winType, 'SIN')
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frameT(:, channel) = frameT(:, channel) .* sinWindowLong(:);
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else
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error('filterbank, l[20]: Unsupported window type input!')
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end
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frameF = mdct4(frameT);
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elseif strcmp(frameType, 'LSS')
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if strcmp(winType, 'KBD')
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frameT(1:1024, channel) = frameT(1:1024, channel) .* kaiserWindowLong(1:1024)';
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frameT(1473:1600, channel) = frameT(1473:1600, channel) .* kaiserWindowShort(129:end)';
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frameT(1601:end, channel) = 0;
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elseif strcmp(winType, 'SIN')
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frameT(1:1024, channel) = frameT(1:1024, channel) .* sinWindowLong(1:1024)';
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frameT(1473:1600, channel) = frameT(1473:1600, channel) .* sinWindowShort(129:end)';
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frameT(1601:end, channel) = 0;
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else
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error('filterbank, l[20]: Unsupported window type input!')
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end
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frameF = mdct4(frameT);
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elseif strcmp(frameType, 'LPS')
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if strcmp(winType, 'KBD')
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frameT(1:448, channel) = 0;
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frameT(449:576, channel) = frameT(449:576, channel) .* kaiserWindowShort(1:128)';
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frameT(1025:end, channel) = frameT(1025:end, channel) .* kaiserWindowLong(1025:end)';
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elseif strcmp(winType, 'SIN')
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frameT(1:448, channel) = 0;
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frameT(449:576, channel) = frameT(449:576, channel) .* sinWindowShort(1:128)';
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frameT(1025:end, channel) = frameT(1025:end, channel) .* sinWindowLong(1025:end)';
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else
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error('filterbank, l[20]: Unsupported window type input!')
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end
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frameF = mdct4(frameT);
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elseif strcmp(frameType, 'ESH')
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% Splits the frame into sub-frames
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[subFrames, ~] = buffer(frameT(449:end-448, channel), 256, 128, 'nodelay');
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if strcmp(winType, 'KBD')
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subFrames = subFrames .* repmat(kaiserWindowShort', [1 8]);
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elseif strcmp(winType, 'SIN')
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subFrames = subFrames .* repmat(sinWindowShort', [1 8]);
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end
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for subFrameIndex = 1:8
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frameF((subFrameIndex - 1) * 128 + 1:subFrameIndex * 128, channel) = mdct4(subFrames(:, subFrameIndex));
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end
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end
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end
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end
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