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120 lines
5.2 KiB
120 lines
5.2 KiB
function [S, sfc, G] = AACquantizer(frameF, frameType, SMR)
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%Implementation of Quantizer
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% Usage [S, sfc, G] = AACquantizer(frameF, frameType, SMR), where:
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% Inputs
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% - frameF is the frame in the frequency domain, in MDCT coefficients
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% representation containing only one of the audio channels stored in
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% a vector of length 1024
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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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% - SMR is the signal to mask ratio array of dimensions 42X8 for
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% EIGHT_SHORT_SEQUENCE frames and 69X1 otherwise
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%
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% Output
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% - S are the MDCT quantization symbols of one audio channel stored
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% in a vector of length 1024
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% - sfc are the scalefactors per band stored in an array of
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% dimensions NBX8 for EIGHT_SHORT_SEQUENCE frames and NBX1
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% otherwise, where NB is the number of bands
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% - G is the global gain stored in an array of dimensions 1X8 for
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% EIGHT_SHORT_SEQUENCE frames and a single value otherwise
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% Declares constant numbers of bands for long and short windows
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LONG_WINDOW_NUMBER_OF_BANDS = 69;
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SHORT_WINDOW_NUMBER_OF_BANDS = 42;
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% Declares persistent variable holding the TNS tables and initializes if empty
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persistent TNSTables;
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if isempty(TNSTables)
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TNSTables = load('TableB219.mat');
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end
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if ~strcmp(frameType, 'ESH')
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T(LONG_WINDOW_NUMBER_OF_BANDS, 1) = 0;
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quantCoeff(LONG_WINDOW_NUMBER_OF_BANDS, 1) = 0;
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sfc(LONG_WINDOW_NUMBER_OF_BANDS, 1) = 0;
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for band = 1:LONG_WINDOW_NUMBER_OF_BANDS
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frameWlow = TNSTables.B219a(band, 2) + 1;
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frameWhigh = TNSTables.B219a(band, 3) + 1;
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subFrameF = frameF(frameWlow:frameWhigh);
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T(band) = sumsqr(subFrameF) ./ SMR(band);
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% Calculates an initial quantization coefficient and attempts
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% quantization
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quantCoeff(band) = 16 * log2(max(frameF) ^ (3 / 4) / 8191) / 3;
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S(frameWlow:frameWhigh, 1) = sign(subFrameF) .* floor(( ...
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abs(subFrameF) .* 2 ^ (-quantCoeff(band) / 4)) ...
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.^ (3 / 4) + 0.4054);
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% Calculates current quantization error
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quantErr = sumsqr(subFrameF - S(frameWlow:frameWhigh));
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% Gradually increases the quantization coefficient
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while quantErr < T(band) && (band > 1 || ...
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(quantErr(band) - quantErr(band - 1) + 1) <= 60)
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quantCoeff(band) = quantCoeff(band) + 1;
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S(frameWlow:frameWhigh) = sign(subFrameF) .* round(( ...
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abs(subFrameF) .* 2 ^ (-quantCoeff(band) / 4)) ...
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.^ (3 / 4) + 0.4054);
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quantErr = sumsqr(subFrameF - S(frameWlow:frameWhigh));
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end
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if band == 1
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sfc(band) = quantCoeff(band);
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else
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sfc(band) = quantCoeff(band) - quantCoeff(band - 1);
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end
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end
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G = quantCoeff(1);
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else
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T(SHORT_WINDOW_NUMBER_OF_BANDS, 1) = 0;
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quantCoeff(SHORT_WINDOW_NUMBER_OF_BANDS, 1) = 0;
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sfc(SHORT_WINDOW_NUMBER_OF_BANDS, 8) = 0;
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G(1, 8) = 0;
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for subFrameIndex = 1:8
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currFrameStart = (subFrameIndex - 1) * 128 + 1;
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currFrameStop = currFrameStart + 127;
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subFrame = frameF(currFrameStart:currFrameStop);
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for band = 1:SHORT_WINDOW_NUMBER_OF_BANDS
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frameWlow = TNSTables.B219b(band, 2);
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frameWhigh = TNSTables.B219b(band, 3);
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subFrameF = subFrame(frameWlow + 1:frameWhigh + 1);
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T(band) = sumsqr(subFrameF) ./ SMR(band);
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% Calculates an initial quantization coefficient and attempts
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% quantization
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quantCoeff(band) = 16 * log2(max(subFrame) ^ (3 / 4) / 8191) / 3;
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S(currFrameStart + frameWlow:currFrameStart + frameWhigh, 1) = sign(subFrameF) .* floor(( ...
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abs(subFrameF) .* 2 ^ (-quantCoeff(band) / 4)) ...
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.^ (3 / 4) + 0.4054);
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% Calculates current quantization error
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quantErr = sumsqr(subFrameF - S(currFrameStart + frameWlow:currFrameStart + frameWhigh));
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% Gradually increases the quantization coefficient
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while quantErr < T(band) && (band > 1 || ...
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(quantErr(band) - quantErr(band - 1) + 1) <= 60)
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quantCoeff(band) = quantCoeff(band) + 1;
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S(currFrameStart + frameWlow:currFrameStart + frameWhigh) = sign(subFrameF) .* round(( ...
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abs(subFrameF) .* 2 ^ (-quantCoeff(band) / 4)) ...
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.^ (3 / 4) + 0.4054);
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quantErr = sumsqr(subFrameF - S(currFrameStart + frameWlow:currFrameStart + frameWhigh));
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end
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if band == 1
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sfc(band, subFrameIndex) = quantCoeff(band);
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else
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sfc(band, subFrameIndex) = quantCoeff(band) - quantCoeff(band - 1);
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end
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end
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G(1, subFrameIndex) = quantCoeff(1);
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end
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end
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end
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