Recent Patents in Signal Processing (January 2015) – Audio coding

For our January 2015 issue, we cover recent patents granted in the area of audio coding. The section below covers patents granted recently for various new audio coding methods, tonal artifact avoidance, and a novel MP3 encoder.

The invention no. 8,848,925 relates to a method and an apparatus in which samples of at least a part of an audio signal of a first channel and a part of an audio signal of a second channel are used to estimate a time delay between said part of the audio signal of said first channel and said part of the audio signal of said second channel. The method includes windowing the samples; performing a time-to-frequency domain transform; and determining an inter-channel time delay between said part of the audio signal of the first channel and said part of the audio signal of said second channel on the basis of the frequency domain representations. There is also disclosed a method and an apparatus for decoding the encoded samples.

In patent no. 8,838,442 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 .pi./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.

Parametric stereo coders in patent no 8,831,759 use perceptually relevant parameters of the input signal to describe spatial properties. One of these parameters is the phase difference between the input signals (ITD or IPD). This time difference only determines the relative time difference between the input signals, without any information about how these time differences should be divided over the output signals in the decoder. An additional parameter is included in the encoded signal that describes how the ITD or IPD should be distributed between the output channels.

An adaptive controller for a configurable audio coding system comprising a fuzzy logic controller modified to use reinforcement learning to create an intelligent control system ia presented in the invention no. 8,819,523. With no knowledge of the external system into which it is placed the audio coding system, under the control of the adaptive controller, is capable of adapting its coding configuration to achieve user set performance goals.

An efficient approach for estimating scalefactors for use in the quantization of audio signal spectrum values is described in patent no 8,799,002. The scalefactor estimation approach can be implemented in multiple stages. A first stage estimates a distortion level for a selected scalefactor band spectrum value based on a received maximum tolerant distortion threshold and the spectrum values in the scalefactor band. A second stage determines an interim process value based on the previously estimated distortion level and generates a scalefactor for a selected scalefactor band spectrum value based on the generated interim process value and a statistically predetermined fraction. A third stage generates a scalefactor that applies to the whole scalefactor band based on the scalefactor generated for the selected scalefactor band spectrum value. The approach provides a performance gain of 40% over previous techniques, thereby reducing device power requirements and audio encoder bottlenecks.

If you have an interesting patent to share when we next feature patents related to audio coding, or if you are especially interested in a signal processing research field that you would want to be highlighted in this section, please send email to Csaba Benedek (benedek.csaba AT sztaki DOT mta DOT hu).

References

Number: 8,848,925
Title: Method, apparatus and computer program product for audio coding 
Inventors:  M. Tammi
Issued:  September 30, 2014
Assignee:  Nokia Corporation (Espoo, FI)

Number: 8,838,442
Title: Method and system for two-step spreading for tonal artifact avoidance in audio coding
Inventors: T.B. Terriberry, J.M. Valin
Issued:  September 16, 2014
Assignee:  Xiph.org Foundation

Number: 8,831,759
Title:  Audio coding
Inventors:      D.J. Breebaart, A.W.J. Oomen
Issued: September 9, 2014   
Assignee:  Koninklijke Philips N.V. (Eindhoven, NL)

Number: 8,819,523
Title:  Adaptive controller for a configurable audio coding system
Inventors:  N. Smyth
Issued:  August 26, 2014
Assignee: Cambridge Silicon Radio Limited (Cambridge, GB)

Number: 8,799,002
Title: Efficient scalefactor estimation in advanced audio coding and MP3 encoder
Inventors:  L. Tang L, K. Ding, Z. Quan
Issued:  August 5, 2014
Assignee: Marvell International Ltd. (Hamilton, BM)