Time warped modified transform coding of audio signals

A decoder for reconstructing an audio signal having a first frame, a second frame following the first frame and a third frame following the second frame, using first warp information, the first warp information describing a pitch information of the audio signal for the first and the second frame, second warp information, the second warp information describing a pitch information of the audio signal for the second and the third frame, first spectral coefficients for the first and the second frame and second spectral coefficients for the second and the third frame, the decoder comprising:

• a spectral value processor adapted
• to derive a first combined frame using the first spectral coefficients and the first warp information, the first combined frame having information on the first and on the second frame;
• and
• to use a first window function for applying weights to sample values of the first combined frame, the first window function depending on the first warp information;
• the spectral value processor further adapted to
• derive a second combined frame using the second spectral coefficients and the second warp information, the second combined frame having information on the second and the third frame;
• and
• to use a second window function for applying weights to sample values of the second combined frame, the second window function depending on the first warp information;
• and
• a synthesizer for reconstructing the second frame using the first combined frame and the second combined frame.

A method of deriving a representation of an audio signal having a first frame, a second frame following the first frame, and a third frame following the second frame, the method comprising:

• estimating first warp information for the first and the second frame and for estimating second warp information for the second frame and the third frame, the warp information describing a pitch information of the audio signal;
• deriving first spectral coefficients for the first and the second frame using the first warp information and a first weighted representation of the first and the second frame, the first weighted representation derived by applying a first window function to the first and the second frames, wherein the first window function depends on the first warp information;
• deriving second spectral coefficients for the second and the third frame using the second warp information and a second weighted representation of the second and the third frame, the second weighted representation derived by applying a second window function to the second and the third frames, wherein the second window function depends on the second warp information;
• and
• outputting the representation of the audio signal including the first and the second spectral coefficients.

A method of reconstructing an audio signal having a first frame, a second frame following the first frame and a third frame following the second frame, using first warp information, the first warp information describing a pitch information of the audio signal for the first and the second frame, second warp information, the second warp information describing a pitch information of the audio signal for the second and the third frame, first spectral coefficients for the first and the second frame and second spectral coefficients for the second and the third frame, the method comprising:

• deriving a first combined frame using the first spectral coefficients and the first warp information, the first combined frame having information on the first and on the second frame;
• using a first window function for applying weights to sample values of the first combined frame, the first window function depending on the first warp information;
• deriving a second combined frame using the second spectral coefficients and the second warp information, the second combined frame having information on the second and the third frame;
• using a second window function for applying weights to sample values of the second combined frame, the second window function depending on the first warp information;
• and
• reconstructing the second frame using the first combined frame and the second combined frame.

A non-transitory computer readable digital storage medium having stored thereon a computer program having a program code for performing, when running on a computer, a method for deriving a representation of an audio signal having a first frame, a second frame following the first frame, and a third frame following the second frame, the method comprising:

• estimating first warp information for the first and the second frame and for estimating second warp information for the second frame and the third frame, the warp information describing a pitch information of the audio signal;
• deriving first spectral coefficients for the first and the second frame using the first warp information and a first weighted representation of the first and the second frame, the first weighted representation derived by applying a first window function to the first and the second frames, wherein the first window function depends on the first warp information;
• deriving second spectral coefficients for the second and the third frame using the second warp information and a second weighted representation of the second and the third frame, the second weighted representation derived by applying a second window function to the second and the third frames, wherein the second window function depends on the second warp information;
• and
• outputting the representation of the audio signal including the first and the second spectral coefficients.

A non-transitory computer readable digital storage medium having stored thereon a computer program having a program code for performing, when running on a computer, a method of reconstructing an audio signal having a first frame, a second frame following the first frame and a third frame following the second frame, using first warp information, the first warp information describing a pitch information of the audio signal for the first and the second frame, second warp information, the second warp information describing a pitch information of the audio signal for the second and the third frame, first spectral coefficients for the first and the second frame and second spectral coefficients for the second and the third frame, the method comprising:

• deriving a first combined frame using the first spectral coefficients and the first warp information, the first combined frame having information on the first and on the second frame;
• using a first window function for applying weights to sample values of the first combined frame, the first window function depending on the first warp information;
• deriving a second combined frame using the second spectral coefficients and the second warp information, the second combined frame having information on the second and the third frame;
• using a second window function for applying weights to sample values of the second combined frame, the second window function depending on the first warp information;
• and
• reconstructing the second frame using the first combined frame and the second combined frame.

An encoder for deriving a representation of an audio signal having a first frame, a second frame following the first frame, and a third frame following the second frame, the encoder comprising:

• a processor comprising:
• a warp estimator for estimating first warp information for the first and the second frame and for estimating second warp information for the second frame and the third frame, the warp information describing a pitch information of the audio signal;
• a spectral analyzer adapted to derive first spectral coefficients for the first and the second frame using the first warp information and a first weighted representation of the first and the second frame, the first weighted representation derived by applying a first window function to the first and the second frames, wherein the first window function depends on the first warp information;
• the spectral analyzer further adapted to
• derive second spectral coefficients for the second and the third frame using the second warp information and a second weighted representation of the second and the third frame, the second weighted representation derived by applying a second window function to the second and the third frames, wherein the second window function depends on the second warp information;
• and
• an output interface for outputting the representation of the audio signal including the first and the second spectral coefficients.