System and method for generating comfort noise
View Patent ↗Comfort noise, such as can be used in voice communications can be generated using methods in the frequency domain and/or in the time domain. In various embodiments, a comfort noise spectrum can be generated in the frequency domain as the product of a background noise sample and a random noise sample. In other embodiments, the comfort noise can be generated directly in the time domain as the convolution of a background noise sample and a random noise sample.
1. A method for generating comfort noise, the method comprising:
obtaining a sample of background noise and voice communications of at least two users in a time domain at a communication device, wherein the communication device is used to transmit and receive the voice communications between the at least two users;
filtering the voice communications from the sample of background noise and voice communications to obtain a filtered sample of background noise;
converting, by the communication device, the filtered sample of background noise, without converting the voice communications of the at least two users, from the time domain to a frequency domain, thereby creating a background noise spectrum in the frequency domain; and
multiplying, by the communication device, the background noise spectrum in the frequency domain by a random white noise spectrum, thereby creating a comfort noise spectrum in the frequency domain.
2. A non-transitory computer readable medium having stored therein instructions for causing a processor to execute the method of claim 1 .
3. The method of claim 1 , further comprising converting the comfort noise spectrum in the frequency domain to the time domain.
4. The method of claim 3 , wherein an inverse Discrete Fourier Transform is used to convert the comfort noise spectrum in the frequency domain to the time domain.
5. The method of claim 3 , further comprising scaling a power level of the comfort noise in the time domain to approximately match a power level of the sample of the background noise in the time domain.
6. The method of claim 1 , wherein converting the sample of background noise from the time domain to a frequency domain comprises performing a Fourier Transform on the sample of background noise in the time domain.
7. The method of claim 1 , wherein the sample of the background noise in the time domain is given by h(k) with 0<=k<N and wherein N is between 80 and 256 inclusive, and wherein converting the sample of background noise from the time domain to a frequency domain comprises taking the N-point Discrete Fourier Transform (“DFT”) of h(k).
8. The method of claim 1 , wherein converting the sample of background noise from the time domain to a frequency domain comprises performing a cosine transform or a sine transform on the sample of background noise in the time domain.
9. The method of claim 8 , wherein the sample of the background noise in the time domain is given by h(k) with 0<=k<N and wherein N is between 80 and 256 inclusive, wherein the background noise spectrum in the frequency domain is given by Y(m), and wherein performing the cosine transform on the sample of background noise in the time domain comprises performing the cosine transform on h(k) according to the formula
Y
(
m
)
-
2
N
∑
k
=
0
N
-
1
h
(
k
)
cos
(
π
(
k
+
0.5
)
(
m
+
0.5
)
N
so as to obtain Y(m).
10. The method of claim 8 , further comprising performing an inverse cosine transform or an inverse sine transform on the comfort noise spectrum in the frequency domain so as to convert the comfort noise spectrum to the time domain.
11. The method of claim 1 , wherein obtaining the sample of background noise in a time domain comprises sampling, at a sampling rate of at least 8000 Hz, a signal on a voice connection currently established between two devices.
12. A method for generating comfort noise, the method comprising:
filtering voice communication from background noise to obtain a background noise segment in a time domain at a communication device;
obtaining a random noise segment in the time domain at the communication device; and
generating, by the communication device, a comfort noise segment in the time domain by convolving the background noise segment and the random noise segment.
13. A non-transitory computer readable medium having stored therein instructions for causing a processor to execute the method of claim 12 .
14. The method of claim 12 , wherein n(k) represents the random noise segment, wherein h(i) represents the background noise segment, wherein x(n) represents the comfort noise segment, and wherein the x(n) is obtained according to the formula
x
(
n
)
=
∑
i
=
0
N
-
1
h
(
i
)
n
(
k
-
i
)
.
15. The method of claim 12 , wherein obtaining a random noise segment in the time domain comprises converting the random noise segment to a random pulse sequence.
16. The method of claim 12 , wherein obtaining a random noise segment in the time domain comprises converting the random noise segment to a random pulse sequence according to the formula
r
(
k
)
=
∑
i
=
0
∞
n
(
i
)
δ
(
k
-
iM
i
)
,
wherein n(i) represents the random noise segment and r(k) represents the random pulse sequence, and wherein {Mi} defines pulse positions and is a sequence of integers such that 0<Mi<N.
17. The method of claim 16 , wherein {Mi} is chosen so as to substantially minimize artificial harmonics.
18. The method of claim 16 , wherein generating a comfort noise segment in the time domain by convolving the background noise segment and the random noise segment comprises generating the comfort noise segment in the time domain by convolving the background noise segment with the random pulse sequence.
19. The method of claim 16 , wherein generating a comfort noise segment in the time domain by convolving the background noise segment and the random noise segment comprises generating the comfort noise segment in the time domain by convolving the background noise segment with the random pulse sequence according to the formula
x
(
k
)
=
∑
i
=
0
∞
n
(
i
)
h
(
n
-
iM
i
)
.
20. A device for voice communications between at least two users, the device including:
a processor;
a memory; and
code stored in the memory and executable on the processor to:
obtain a sample of background noise and voice communications of the at least two users in a time domain,
filter the voice communications from the sample of background and voice communications to obtain a filtered sample of background noise,
convert the filtered sample of background noise, without converting the voice communications of the at least two users, from the time domain to a frequency domain, thereby creating a background noise spectrum in the frequency domain,
multiply the background noise spectrum in the frequency domain by a random white noise spectrum, thereby creating a comfort noise spectrum in the frequency domain,
convert the comfort noise spectrum in the frequency domain to a time domain, and
output the comfort noise to a user of the device.