Method and system for two-step spreading for tonal artifact avoidance in audio coding

A method of coding an audio signal in an audio coding system comprising a decoder circuit coupled to an encoder circuit, the method comprising:

• grouping frequency domain coefficients generated by a transform function performed on an input audio signal into a plurality of partitions, wherein each partition spans some subset of frequencies in a band, and wherein each partition is coded by the processor-based device using a defined number of bits, and further wherein the frequency domain coefficients are coded using one or more codebooks;
• arranging the coefficients for a first partition into a linear array;
• computing a gain factor for the bits of first partition;
• deriving a rotation angle for successive pairs of coefficients of the linear array based on the gain factor, wherein the rotation angle is between π/4 and π/2;
• and
• applying one or more rotation operations to successive pairs of coefficients in the linear array using a defined rotation angle and a defined stride length for each rotation operation of the one or more rotation operations, wherein the one or more rotation operations includes a rotation operation in which the defined stride length is a unity distance between members of the successive pairs of coefficients.

A system for coding an audio signal, comprising:

• a first decoder component in a decoder circuit grouping frequency domain coefficients generated by a transform function performed on an input audio signal into a plurality of partitions, wherein each partition spans some subset of frequencies in a band, and wherein each partition is coded by the processor-based device using a defined number of bits, and further wherein the frequency domain coefficients are coded using one or more codebooks;
• a second decoder component arranging the coefficients for a first partition into a linear array, computing a gain factor for the bits of first partition;
• and
• a first coefficient spreading function executed by the decoder component and deriving a rotation angle for successive pairs of coefficients of the linear array based on the gain factor, wherein the rotation angle is between π/4 and π/2, and applying one or more rotation operations to successive pairs of coefficients in the linear array using a defined rotation angle and a defined stride length for each rotation operation of the one or more rotation operations, wherein the one or more rotation operations includes a rotation operation in which the defined stride length is a unity distance between members of the successive pairs of coefficients.