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78 lines
3.2 KiB
78 lines
3.2 KiB
function frameType = SSC(~, nextFrameT, prevFrameType)
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%Implementation of the Sequence Segmentation Control step
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% Usage frameType = SSC(frameT, nextFrameT, prevFrameType), 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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% - nextFrameT is the next frame in the time domain, containing both
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% channels of the audio stored in an array of dimensions 2048X2
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% - prevFrameType is the type of the previous 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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%
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% Output
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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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% Examines the cases where the determination of the type of the next
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% frame isn't needed for
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if strcmp(prevFrameType, 'LSS')
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frameType = 'ESH';
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return;
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elseif strcmp(prevFrameType, 'LPS')
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frameType = 'OLS';
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return;
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end
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% Determines the type of the next frame
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% Filters frame
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nextFrameT = filter([0.7548 -0.7548], [1 -0.5095], nextFrameT, [], 1);
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channelFrameType = {'nan', 'nan'};
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for channel = 1:2
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% Calculates sub-frame energy estimation
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[subFrames, ~] = buffer(nextFrameT(577:end - 448, channel), 128, 0, 'nodelay');
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energyEstimations = sum(subFrames .^ 2, 1);
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% Calculates the ratio of the sub-frame energy to the average energy of
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% the previous sub-frames
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energyRatios = movmean(energyEstimations, [8 0]);
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energyRatios = energyEstimations ./ [energyEstimations(1) energyRatios(1:end-1)];
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if ~isempty(find(energyEstimations > 10^(-3), 1)) && ...
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~isempty(find(energyRatios(energyEstimations > 10^(-3)) > 10, 1))
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% Next frame is ESH
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if strcmp(prevFrameType, 'ESH')
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% This frame of this channel is an EIGHT_SHORT_SEQUENCE type
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% frame. This means the frames of both channels will be encoded
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% as EIGHT_SHORT_SEQUENCE type frames.
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frameType = 'ESH';
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return;
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elseif strcmp(prevFrameType, 'OLS')
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channelFrameType{channel} = 'LSS';
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end
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else
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if strcmp(prevFrameType, 'ESH')
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channelFrameType{channel} = 'LPS';
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elseif strcmp(prevFrameType, 'OLS')
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channelFrameType{channel} = 'OLS';
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end
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end
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end
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% Joins decision for both channels
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if strcmp(channelFrameType{1}, 'nan') || strcmp(channelFrameType{2}, 'nan')
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error('SSC, l[73]: Internal error occurred!')
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end
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if strcmp(channelFrameType{1}, 'OLS')
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frameType = channelFrameType{2};
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elseif strcmp(channelFrameType{2}, 'OLS')
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frameType = channelFrameType{1};
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elseif strcmp(channelFrameType{1}, channelFrameType{2})
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frameType = channelFrameType{1};
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else
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frameType = 'ESH';
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end
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end
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