Audio encoder and decoder for encoding frames of sampled audio signals

A method for encoding frames of a sampled audio signal to acquire encoded frames, wherein a frame comprises a number of time domain audio samples, comprising:

• determining, performed by a predictive coding analysis stage, information on coefficients of a synthesis filter and information on a prediction domain frame based on a frame of audio samples;
• transforming, performed by a frequency domain transformer, a frame of audio samples to the frequency domain to acquire a frame spectrum;
• deciding, performed by an encoding domain decider, whether encoded data for a frame is based on the information on the coefficients and on the information on the prediction domain frame, or based on the frame spectrum;
• determining, performed by a controller, information on a switching coefficient when it is decided that encoded data of a current frame is based on the information on the coefficients and the information on the prediction domain frame when encoded data of a previous frame was encoded based on a previous frame spectrum acquired by the frequency domain transformer;
• and
• encoding, performed by a redundancy reducing encoder, the information on the prediction domain frame, the information on the coefficients, the information on the switching coefficient and/or the frame spectra,
• wherein the information on the switching coefficient comprises an information enabling an initialization of a predictive synthesis stage, and the determination of the information on the switching coefficient is performed based on an LPC analysis of the previous frame, and
• the controller is adapted for determining the information on the switching coefficient based on a high pass filtered version of a decoded frame spectrum of the previous frame,
• wherein at least one of the predictive coding analysis stage, the frequency domain transformer, the encoding domain decider, the controller and the redundancy reducing encoder comprises a hardware implementation.

An audio decoder apparatus for decoding encoded frames to acquire frames of a sampled audio signal, wherein a frame comprises a number of time domain audio samples, comprising:

• a redundancy retrieving decoder for decoding the encoded frames to acquire information on a prediction domain frame, information on coefficients for a synthesis filter and/or a frame spectrum;
• a predictive synthesis stage for determining a predicted frame of audio samples based on the information on the coefficients for the synthesis filter and the information on the prediction domain frame;
• a time domain transformer for transforming the frame spectrum to the time domain to acquire a transformed frame from the frame spectrum;
• a combiner for combining the transformed frame and the predicted frame to acquire the frames of the sampled audio signal;
• and
• a controller for controlling a switch-over process, the switch-over process being effected when a previous frame is based on a transformed frame and a current frame is based on a predicted frame, the controller being configured for providing a switching coefficient to the predictive synthesis stage for initialization of the predictive synthesis stage by estimating an LPC filter corresponding to an end of the previous frame so that the predictive synthesis stage is initialized when the switch-over process is effected,
• wherein at least one of the redundancy retrieving decoder, the predictive synthesis stage, the time domain transformer, the combiner and the controller comprises a hardware implementation.

A method for decoding encoded frames to acquire frames of a sampled audio signal, wherein a frame comprises a number of time domain audio samples, comprising:

• decoding, performed by a redundancy retrieving decoder, the encoded frames to acquire information on a prediction domain frame, and information on coefficients for a synthesis filter and/or a frame spectrum;
• determining, performed by a predictive synthesis stage, a predicted frame of audio samples based on the information of the coefficients for the synthesis filter and the information on the prediction domain frame;
• transforming, performed by a time domain transformer, the frame spectrum to the time domain to acquire a transformed frame from the frame spectrum;
• combining, performed by a combiner, the transformed frame and the predicted frame to acquire the frames of the sampled audio signal;
• and
• controlling, performed by a controller, a switch-over process, the switch-over process being effected when a previous frame is based on the transformed frame, and a current frame is based on thr predicted frame;
• providing, performed by the controller, a switching coefficient for initialization by estimating an LPC filter corresponding to an end of the previous frame so that a predictive synthesis stage is initialized when the switch-over process is effected,
• wherein at least one of the redundancy retrieving decoder, the predictive synthesis stage, the time domain transformer, the combiner and the controller comprises a hardware implementation.

A non-transitory computer-readable storage medium having stored thereon a computer program comprising a program code for performing, when a computer program runs on a computer or processor, the method for encoding frames of a sampled audio signal to acquire encoded frames, wherein a frame comprises a number of time domain audio samples, comprising:

• determining information on coefficients of a synthesis filter and information on a prediction domain frame based on a frame of audio samples;
• transforming a frame of audio samples to the frequency domain to acquire a frame spectrum;
• deciding whether encoded data for a frame is based on the information on the coefficients and on the information on the prediction domain frame, or based on the frame spectrum;
• determining information on a switching coefficient when it is decided that encoded data of a current frame is based on the information on the coefficients and the information on the prediction domain frame when encoded data of a previous frame was encoded based on a previous frame spectrum acquired by the frequency domain transformer;
• and
• encoding the information on the prediction domain frame, the information on the coefficients, the information on the switching coefficient and/or the frame spectra,
• wherein the information on the switching coefficient comprises an information enabling an initialization of a predictive synthesis stage, and the determination of the information on the switching coefficient is performed based on an LPC analysis of the previous frame, and
• the controller is adapted for determining the information on the switching coefficient based on a high pass filtered version of a decoded frame spectrum of the previous frame.

A non-transitory computer-readable storage medium having stored thereon a computer program comprising a program code for performing, when a computer program runs on a computer or processor, the method for decoding encoded frames to acquire frames of a sampled audio signal, wherein a frame comprises a number of time domain audio samples, comprising:

• decoding the encoded frames to acquire information on a prediction domain frame, and information on coefficients for a synthesis filter and/or a frame spectrum;
• determining a predicted frame of audio samples based on the information of the coefficients for the synthesis filter and the information on the prediction domain frame;
• transforming the frame spectrum to the time domain to acquire a transformed frame from the frame spectrum;
• combining the transformed frame and the predicted frame to acquire the frames of the sampled audio signal;
• and
• controlling a switch-over process, the switch-over process being effected when a previous frame is based on the transformed frame, and a current frame is based on thr predicted frame;
• providing a switching coefficient for initialization by estimating an LPC filter corresponding to an end of the previous frame so that a predictive synthesis stage is initialized when the switch-over process is effected.