MDCT-Domain Error Concealment

A decoding system for concealing errors in packets of data that are to be decoded in a modified discrete cosine transform (MDCT) based audio decoder arranged to decode a sequence of packets into a sequence of decoded frames, the system comprising:

• a receiver section configured to receive, from an MDCT based audio encoder arranged to encode an audio signal, a packet comprising a set of MDCT coefficients associated with a frame comprising time-domain samples of the audio signal;
• an error detection section configured to identify the received packet to be an erroneous packet in that the received packet comprises one or more errors;
• and
• an error concealment section configured to:
• generate estimated MDCT coefficients to replace the set of MDCT coefficients of the erroneous packet, the estimated MDCT coefficients being based on corresponding MDCT coefficients associated with a received packet, which directly precedes the erroneous packet in the sequence of packets;
• assign signs of a first subset of MDCT coefficients of the estimated MDCT coefficients, wherein the first subset comprises such MDCT coefficients that are associated with tonal-like spectral bins of the packet, to be equal to corresponding signs of the corresponding MDCT coefficients of the received packet, which directly precedes the erroneous packet in the sequence of packets;
• randomly assign signs of a second subset of MDCT coefficients of the estimated MDCT coefficients, wherein the second subset comprises such MDCT coefficients that are associated with noise-like spectral bins of the packet;
• generate a concealment packet based on the estimated MDCT coefficients and the selected signs of the packet;
• and
• replacing the erroneous packet with the concealment packet.

A method for concealing errors in packets of data that are to be decoded in a modified discrete cosine transform (MDCT) based audio decoder arranged to decode a sequence of packets into a sequence of decoded frames, the method comprising:

• receiving, from an MDCT based audio encoder arranged to encode an audio signal, a packet comprising N/2 MDCT coefficients associated with N windowed time-domain samples of the audio signal;
• identifying the packet to be an erroneous packet in that the packet comprises one or more errors;
• estimating a first subset comprising N/4 windowed time-domain aliased samples of a first half of an intermediate frame comprising N windowed time-domain aliased samples associated with the erroneous packet, the estimation being based on relations between windowed time-domain aliased samples of the first subset and windowed time-domain samples of the N windowed time-domain samples of the audio signal;
• and
• estimating a second subset comprising remaining N/4 windowed time-domain aliased samples of the first half of the intermediate frame based on symmetry relations between windowed time-domain aliased samples of the second subset and windowed time-domain aliased samples of the first subset.

A decoding system for concealing errors in packets of data that are to be decoded in a modified discrete cosine transform (MDCT) based audio decoder arranged to decode a sequence of packets into a sequence of decoded frames, the system comprising:

• a receiver section configured to receive, from an MDCT based audio encoder arranged to encode an audio signal, a packet comprising N/2 MDCT coefficients associated with N windowed time-domain samples of the audio signal;
• an error detection section configured to identify the packet to be an erroneous packet in that the packet comprises one or more errors;
• an error concealment section configured to:
• estimating a first subset comprising N/4 windowed time-domain aliased samples of a first half of an intermediate frame comprising N windowed time-domain aliased samples associated with the erroneous packet, the estimation being based on relations between windowed time-domain aliased samples of the first subset and windowed time-domain samples of the N windowed time-domain samples of the audio signal, and
• estimate a second subset comprising remaining N/4 windowed time-domain aliased samples of the first half of the intermediate frame based on symmetry relations between windowed time-domain aliased samples of the second subset and windowed time-domain aliased samples of the first subset.