Cross product enhanced subband block based harmonic transposition

A system configured to generate a time stretched and/or frequency transposed signal from an input signal, the system comprising one or more processing elements that:

• derive a number Y ≥1 of analysis subband signals from the input signal, wherein each analysis subband signal comprises a plurality of complex-valued analysis samples, each having a phase and a magnitude;
• generate a synthesis subband signal from the Y analysis subband signals using a subband transposition factor Q and a subband stretch factor S, at least one of Q and S being greater than one by:
• forming Y frames of L input samples, each frame being extracted from said plurality of complex-valued analysis samples in an analysis subband signal, wherein L is a frame length greater than 1, and wherein at least one of the L input samples is derived by interpolating two or more of the plurality of complex-valued analysis samples;
• applying a block hop size of h samples to said plurality of complex-valued analysis samples, prior to forming a subsequent frame of L input samples, thereby generating a sequence of frames of input samples;
• generating, on the basis of Y corresponding frames of input samples, a frame of processed samples by determining a phase and magnitude for each processed sample of the frame, wherein, for at least one processed sample:
• i) the phase of the processed sample is based on the respective phases of corresponding input samples in each of the Y frames of input samples;
• and
• ii) the magnitude of the processed sample is determined as a mean value of the magnitude of the corresponding input sample in a first frame of the Y frames of input samples and the magnitude of the corresponding input sample in a second frame of the Y frames of input samples;
• applying a window function of a length which corresponds to the frame length L to the frame of processed samples;
• and
• determining the synthesis subband signal by overlapping and adding the samples of a sequence of frames of processed samples;
• and
• generating the time stretched and/or frequency transposed signal from the synthesis subband signal, wherein the system is operable at least for Y=2.