Transform encoding/decoding of harmonic audio signals

A method of audio signal reconstruction comprising:

• receiving an encoded frequency transformed harmonic audio signal;
• decoding the encoded frequency transformed harmonic audio signal and thereby obtaining a reconstructed frequency transformed harmonic audio signal, based on:
• decoding spectral peak regions of the encoded frequency transformed harmonic audio signal, said spectral peak regions comprising spectral peaks having magnitudes exceeding a predetermined frequency dependent threshold;
• decoding at least one low-frequency set of Modified Discrete Cosine Transform (MDCT) coefficients of the encoded frequency transformed harmonic audio signal;
• distributing the MDCT coefficients of each low-frequency set outside the spectral peak regions and below a crossover frequency that depends on a number of bits used to encode the peak regions;
• decoding a noise-floor gain of at least one high-frequency set of MDCT coefficients of the encoded frequency transformed harmonic audio signal that are outside of the spectral peak regions;
• filling each high-frequency set of MDCT coefficients with noise having the corresponding decoded noise-floor gain;
• and
• outputting the reconstructed frequency transform harmonic audio signal.

An encoder for encoding a frequency transformed harmonic audio signal, said encoder configured to obtain the frequency transformed harmonic audio signal and comprising a processing circuit configured to:

• generate an encoded frequency transformed harmonic audio signal corresponding to the frequency transformed harmonic audio signal, based on being configured to:
• locate spectral peaks in the frequency transformed harmonic audio signal that have magnitudes exceeding a predetermined frequency dependent threshold;
• encode peak regions including and surrounding the located spectral peaks;
• encode at least one low-frequency set of Modified Discrete Cosine Transform (MDCT) coefficients outside the peak regions and below a crossover frequency that depends on a number of bits used to encode the peak regions;
• and
• encode a noise-floor gain of at least one high-frequency set of not yet encoded MDCT coefficients outside the peak regions;
• and
• output the encoded frequency transformed harmonic audio signal.

A decoder configured for audio signal reconstruction, said decoder configured to receive an encoded frequency transformed harmonic audio signal and comprising a processing circuit configured to:

• decode the encoded frequency transformed harmonic audio signal and thereby obtain a reconstructed frequency transformed harmonic audio signal, based on being configured to:
• decode spectral peak regions of the encoded frequency transformed harmonic audio signal, said spectral peak regions including spectral peaks having magnitudes exceeding a predetermined frequency dependent threshold;
• decode at least one low-frequency set of Modified Discrete Cosine Transform (MDCT) coefficients;
• distribute the MDCT coefficients of each low-frequency set outside the spectral peak regions and below a crossover frequency that depends on a number of bits used to encode the peak regions;
• decode a noise-floor gain of at least one high-frequency set of MDCT coefficients outside of the spectral peak regions;
• and
• fill each high-frequency set of MDCT coefficients with noise having the corresponding noise-floor gain;
• and
• output the reconstructed frequency transformed harmonic audio signal.