Downscaled decoding
AssigneeFraunhofer-Gesellschaft zur Foerderung der angewandten Forschung e.V.
InventorsMarkus SCHNELL, Manfred LUTZKY, Eleni FOTOPOULOU, Konstantin SCHMIDT, Conrad BENNDORF, Adrian TOMASEK, Tobias ALBERT, Timon SEIDL
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Abstract
A downscaled version of an audio decoding procedure may more effectively and/or at improved compliance maintenance be achieved if the synthesis window used for downscaled audio decoding is a downsampled version of a reference synthesis window involved in the non-downscaled audio decoding procedure by downsampling by the downsampling factor by which the downsampled sampling rate and the original sampling rate deviate, and downsampled using a segmental interpolation in segments of 1/4 of the frame length.
Claims23
An audio decoder comprising:
- a receiver configured to receive, for each of frames of an audio signal, a spectrum forming a spectral decomposition of a temporal portion comprising the respective frame and N−1 previous frames, with N being an integer;
- a grabber configured to grab-out for each frame, a low-frequency fraction of 1/F, in length, of the spectrum;
- a spectral-to-time modulator configured to subject, for each frame, the low-frequency fraction to an inverse transform so as to acquire a temporal representation of the temporal portion;
- a windower configured to window, for each frame, the temporal representation of the temporal portion using a synthesis window comprising a zero-portion of 1/4 of a frame length at a leading end thereof and comprising a peak within a temporal interval of the synthesis window, which succeeds the zero-portion, so that the windower acquires a windowed temporal representation of the temporal portion;
- and
- a time domain aliasing canceler configured to subject the windowed temporal representation of the temporal portion of the frames to an overlap-add process at a mutual inter-frame distance corresponding to the frame length,
- wherein the inverse transform is an inverse MDCT or inverse MDST, and
- wherein the synthesis window is a downsampled version of a reference synthesis window, downsampled by a factor of F by a segmental interpolation in 4·N segments of mutually equal segment length.
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A method for decoding an audio signal, the method comprising:
- receiving, for each of frames of the audio signal, a spectrum forming a spectral decomposition of a temporal portion comprising the respective frame and N−1 previous frames, with N being an integer;
- grabbing-out for each frame, a low-frequency fraction of 1/F, in length, of the spectrum;
- performing a spectral-to-time modulation by subjecting, for each frame, the low-frequency fraction to an inverse transform so as to acquire a temporal representation of the temporal portion;
- windowing, for each frame, the temporal representation of the temporal portion using a synthesis window comprising a zero-portion of 1/4 of a frame length at a leading end thereof and comprising a peak within a temporal interval of the synthesis window, which succeeds the zero-portion, so that a windowed temporal representation of the temporal portion is acquired;
- and
- performing a time domain aliasing cancellation by subjecting the windowed temporal representation of the temporal portion of the frames to an overlap-add process at a mutual inter-frame distance corresponding to the frame length,
- wherein the inverse transform is an inverse MDCT or inverse MDST, and
- wherein the synthesis window is a downsampled version of a reference synthesis window, downsampled by a factor of F by a segmental interpolation in 4·N segments of mutually equal segment length.
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Dependencies are inferred from the claim text.