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

摘要

Embodiments are directed to an audio coding scheme implemented in a codec that eliminates birdie artifacts generated by transform coding methods. A frequency coefficient spreading method invertibly rotates a spectrum of coefficient values based on a defined rotation angle, The rotated spectrum is then quantized, and the rotation operation is then reversed so that a previously sparse spectrum (i.e., one with few non-zero values) becomes one that has many non-zero values. The method arranges the coefficients for a particular partition into a linear array and computes a gain factor for the partition. A rotation angle of between 0 and π/4 for successive pairs of coefficients of the linear array based on the gain factor is then derived. One or more rotation operations are then applied to successive pairs of coefficients in the linear array using a specific rotation angle and a stride length for each rotation operation.

主权项

1. A method of transforming a first spectrum having few non-zero values into a spectrum having a large number of non-zero values, the sparse spectrum including a number N of points lying in a plane, the method comprising:
defining, by a processor-based device, a rotation angle for rotating successive pairs of points of the first spectrum, wherein the rotation angle is between π/4 and π/2, the processor-based device being executed on a computer having a non-transitory computer readable medium storing a plurality of instructions executable by one or more processors; applying, by the processor-based device, a first rotation operation using the rotation angle on a first set of successive pairs of points, wherein members of each pair of points of the first set of successive pairs of points are separated by a first stride length; and applying, by the processor-based device, a second rotation operation using a second rotation angle on a different set of successive pairs of points, wherein members of each pair of points of the different set of successive pairs of points are separated by a second stride length.