Spectral shape estimation from mdct coefficients

A decoder configured to control a concealment method for a lost audio frame associated with a received audio signal, the decoder apparatus comprising:

• a processor;
• and
• a memory storing instructions that, when executed by the processor, cause the decoder to perform operations comprising:
• decoding a first audio frame of the received audio signal to obtain modified discrete cosine transform, MDCT coefficients;
• determining values of a first spectral shape based upon MDCT coefficients decoded from the first audio frame decoded, the first spectral shape comprising a number of sub-bands;
• decoding a second audio frame of the received audio signal;
• determining values of a second spectral shape based upon MDCT coefficients decoded from the second audio frame decoded, the second spectral shape comprising the number of sub-bands;
• transforming the values of the first spectral shape and a first frame energy of the first audio frame into a first representation of a first fast Fourier transform, FFT, based spectral analysis and transforming the values of the second spectral shape and a second frame energy of the second audio frame into a second representation of a second FFT spectral analysis;
• detecting, based on the first representation of the first FFT and the second representation of a second FFT, a transient condition;
• and
• responsive to detecting the transient condition, modifying the concealment method by selectively adjusting a spectrum magnitude of a substitution frame spectrum.