Apparatus and a method for unwrapping phase differences

Patent metadata

Field	Value
Publication number	US-10834505-B2
Application number	US-201916424147-A
Country	US
Kind code	B2
Filing date	May 28, 2019
Priority date	Nov 28, 2016
Publication date	Nov 10, 2020
Grant date	Nov 10, 2020

Abstract

An apparatus configured to obtain a plurality of phase differences is provided. Each phase difference represents a difference in phase between a spectral component in a first sound signal and a corresponding spectral component in a second sound signal, to estimate an aliasing frequency. Phase differences in frequency bands above the aliasing frequency are expected to be wrapped, and to unwrap the plurality of phase differences in dependence on the estimated aliasing frequency. A phase difference obtained from spectral components that are comprised in one frequency band is unwrapped independently of any phase difference obtained from spectral components that are comprised in another frequency band.

First claim

What is claimed is:

1. An apparatus comprising a processor that is configured to:
obtain a plurality of phase differences, wherein each phase difference represents a difference in phase between (i) a spectral component in a first sound signal captured by a first microphone, and (ii) a spectral component in a second sound signal captured by a second microphone,
wherein each spectral component is part of a signal spectrum for its respective sound signal,
wherein each signal spectrum represents its respective sound signal as a plurality of spectral components, and
wherein each spectral component is comprised in a respective frequency band of a plurality of frequency bands representing the respective sound signal;

estimate an aliasing frequency; and
unwrap the plurality of phase differences in dependence on the estimated aliasing frequency, including determining a wrapping direction for unwrapping each phase difference by assigning each phase difference to one of one or more sets, wherein:
(a) each set comprises phase differences obtained from spectral components that are comprised in a particular segment of the plurality of frequency bands of the first and second sound signals; and
(b) each phase difference is assigned to one of the sets in dependence on the estimated aliasing frequency, such that none of the phase differences assigned to a particular set is wrapped relative to the other phase differences assigned to the same set;

fit a line to each set of phase differences; and
estimate the wrapping direction in dependence on slopes of the lines fitted to the sets of phase differences,
wherein each phase difference obtained from spectral components that are comprised in one frequency band is unwrapped independently of any phase difference obtained from spectral components that are comprised in another frequency band.

2. The apparatus as claimed in claim 1 , wherein the phase differences are obtained from spectral components in more than three of the plurality of frequency bands that are comprised in the first and second sound signals.

3. The apparatus as claimed in claim 1 , wherein the processor is further configured to estimate the aliasing frequency in dependence on a fundamental frequency associated with the phase differences obtained from the spectral components that are comprised in the first and second sound signals.

4. The apparatus as claimed in claim 1 , wherein the processor is further configured to unwrap the phase difference obtained from spectral components comprised in a particular frequency band by determining the unwrapped phase difference to be:

Φ
i
″

=

Φ
i

+

2
⁢

k
d

⁢

⌊

N
a

+
i

2
⁢

N
a

⌋

⁢
π

where Φ i ′ is the unwrapped phase difference for frequency band i between a spectral component comprised in the first sound signal that is comprised in frequency band i and a spectral component comprised in the second sound signal that is also comprised in frequency band i, Φ i is the wrapped phase difference for frequency band i between a spectral component comprised in the first sound signal that is comprised in frequency band i and a spectral component comprised in the second sound signal that is also comprised in frequency band i, N a is a frequency band associated with the estimated aliasing frequency, k d is an unwrapping direction, and └ ┘ denotes a floor function.

5. The apparatus as claimed in claim 1 , wherein before estimating the aliasing frequency, the processor is further configured to:
for each spectral component in the first and second sound signals, obtain a covariance matrix that represents the covariance of corresponding spectral components in the first and second sound signals and determine an eigenvalue associated with an eigenvector of that matrix;
identify any spectral components in the first and second sound signals that are associated with a covariance matrix that has an eigenvalue that is below a predetermined threshold;
disregard any phase difference that was obtained from one of the identified spectral components when estimating the aliasing frequency;
determine a replacement phase difference by interpolating between phase differences obtained from spectral components that were identified as having covariance matrices with eigenvalues above the predetermined threshold; and
replace a disregarded phase difference with a replacement phase difference.

6. The apparatus as claimed in claim 1 , wherein the processor is further configured to determine the wrapping direction in dependence on spectral components in more than three of the plurality of frequency bands that are comprised in the first and second sound signals and to unwrap the plurality of phase differences in dependence on the wrapping direction.

7. The apparatus as claimed in claim 1 , wherein before fitting the lines to the set of phase differences for estimating the wrapping direction, the processor is further configured to denoise the phase differences in each set by:
identifying any phase differences that should be classified as noise by determining a distance between each phase difference in a respective set and the line fitted to that set and classifying as noise any phase difference that is associated with a distance greater than an adaptive threshold, wherein the adaptive threshold is determined in dependence on a number of phase differences that are respectively above or below the line fitted to each set; and
removing any phase differences that are classified as being noise from their respective set.

8. The apparatus as claimed in claim 1 , wherein the processor is further configured to, after unwrapping the plurality of phase differences:
identify a phase difference that has been unwrapped incorrectly in dependence on a difference between an unwrapped phase difference obtained from spectral components comprised in a particular frequency band and a phase difference that is predicted for that frequency band by the slope of the line fitted to the unwrapped phase differences.

9. The apparatus as claimed in claim 8 , wherein the processor is further configured to determine whether or not the phase differences should be unwrapped by:
summing the plurality of phase differences to obtain a first sum;
for each frequency band, determining a difference between an unwrapped phase difference obtained from spectral components comprised in that particular frequency band and a phase difference that is predicted for that frequency band by the slope of the line fitted to the unwrapped phase differences;
summing the differences determined for the plurality of frequency bands to obtain a second sum; and
determining whether or not the phase differences should be unwrappe

Assignees

• Huawei Tech Duesseldorf Gmbh

Inventors

• Geiger Jürgen
• Chen Kainan
• Grosche Peter

Classifications

• G01S3/8006 Primary

  Multi-channel systems specially adapted for direction-finding, i.e. having a single aerial system capable of giving simultaneous indications of the directions of different signals · CPC title

• H04R29/005

  Microphone arrays · CPC title

• G01S3/8083

  determining direction of source · CPC title

• G10L21/0232

  Processing in the frequency domain · CPC title

• H04R1/406

  microphones · CPC title