US5400394A — Adaptive echo canceller for voice messaging system

Claim 1

Independent Claim 178 words

A method of adaptive echo cancellation in a voice messaging or voice response system having a memory store, at least one digital signal processor, a digital voice data receive data line, a transmit data line, and an echo canceller apparatus comprising a digital adapt filter having a plurality of adapt filter coefficients, a digital cancel filter coupled to the adapt filter and an adaptation control means for controlling transfer of the adapt filter coefficients to the cancel filter, the method comprising the steps of: identifying a successive quantity of voice data frames on the transmit data line which pass a power criterion and storing the frames in a buffer; truncating a plurality of segments from each data frame, and for each segment, deriving adapt filter coefficients from a plurality of taps in each segment during all available computing cycles of the digital signal processor; selecting successive adjacent windows of taps from the adapt filter coefficents and identifying by an energy level test the best window; and transferring adapt filter coefficients in the best window to the cancel filter.

Claim 2

Independent Claim 178 words

A method of adaptive echo cancellation in a voice messaging or voice response system having a memory store, at least one digital signal processor, a digital voice data receive data line, a transmit data line, and an echo canceller apparatus comprising a digital adapt filter having a plurality of adapt filter coefficients, a digital cancel filter coupled to the adapt filter and an adaptation control means for controlling transfer of the adapt filter coefficients to the cancel filter, the method comprising the steps of: identifying a successive quantity of voice data frames on the transmit data line which pass a power criterion and storing the frames in a buffer; truncating a plurality of segments from each data frame, and for each segment, deriving adapt filter coefficients from a plurality of taps in each segment during all available computing cycles of the digital signal processor; selecting successive adjacent windows of taps from the adapt filter coefficents and identifying by an energy level test the best window; and transferring adapt filter coefficients in the best window to the cancel filter.

Claim 3

Dependent Claim 37 words

The method of claim 1, wherein the cancel filter is arranged to cause echo cancellation on an input signal on the receive data line in real-time and wherein the adapt filter is operative on buffered data frames.

Claim 4

Dependent Claim 55 words

The method of claim 1, wherein the truncating step further comprises the step of testing whether processing cycles of the digital signal processor are available for use, and if so, for setting a boolean variable and for causing the adapt filter to perform further echo cancellation functions responsive to the value of the boolean variable.

Claim 5

Dependent Claim 44 words

A method as defined in claim 1 further comprising the initial steps of: transmitting a burst of white noise on the transmit data line; combining a tone signal with the burst; and sensing the burst and defining preliminary adapt filter coefficients in response thereto.

Claim 6

Independent Claim 209 words

A method for providing echo cancellation signals in a voice messaging or voice response system having a memory store and a mass storage device and at least one digital signal processor providing a receive data line and a transmit data line and being coupled to the memory store and the mass storage device, the method comprising the steps of: coupling an adapt filter to the receive data line and to the transmit data line and to the digital signal processor; coupling a cancel filter to the adapt filter; identifying a successive plurality of data frames on the receive data line meeting a power criteria test; storing the successive plurality of data frames in a convergence buffer in the memory store; deriving a plurality of adapt filter coefficients from the successive plurality of data frames; selecting successive windowed quantities of taps from each of the adapt filter coefficients; identifying a best windowed quantity having the most signal energy of successive windowed quantities; generating a delay value signal using the plurality of adapt filter coefficients; transferring the delay value and a subset of the adapt filter coefficients corresponding to the best windowed quantity to the cancel filter; and generating a cancel echo signal proportional to a plurality of cancel filter coefficients.

Claim 7

Independent Claim 209 words

A method for providing echo cancellation signals in a voice messaging or voice response system having a memory store and a mass storage device and at least one digital signal processor providing a receive data line and a transmit data line and being coupled to the memory store and the mass storage device, the method comprising the steps of: coupling an adapt filter to the receive data line and to the transmit data line and to the digital signal processor; coupling a cancel filter to the adapt filter; identifying a successive plurality of data frames on the receive data line meeting a power criteria test; storing the successive plurality of data frames in a convergence buffer in the memory store; deriving a plurality of adapt filter coefficients from the successive plurality of data frames; selecting successive windowed quantities of taps from each of the adapt filter coefficients; identifying a best windowed quantity having the most signal energy of successive windowed quantities; generating a delay value signal using the plurality of adapt filter coefficients; transferring the delay value and a subset of the adapt filter coefficients corresponding to the best windowed quantity to the cancel filter; and generating a cancel echo signal proportional to a plurality of cancel filter coefficients.

Claim 8

Dependent Claim 65 words

A method as defined in claim 5 wherein the step of generating a cancel echo signal is accomplished in real time and wherein the step of deriving the adapt filter coefficients from the successive plurality of data frames further comprises the step of operating on a plurality of segments truncated from each of the data frames in non-real time during playback of a voicefile message.

Claim 9

Dependent Claim 53 words

A method as defined in claim 5 further comprising the steps of: testing whether processing cycles of the digital signal processor are available for use; setting a value of a boolean variable if cycles are available; and causing further echo cancellation functions to be performed responsive to the value of the boolean variable.

Claim 10

Dependent Claim 63 words

A method as defined in claim 5 wherein the step of identifying a best windowed quantity comprises the steps of: storing each selected successive windowed quantity of taps from the adapt coefficients; computing a sum of squares of each adapt coefficient of the taps in each selected successive windowed quantity; and comparing the sums of the squares to determine a best windowed quantity.

Claim 11

Dependent Claim 41 words

A method as defined in claim 5 further comprising the initial steps of: transmitting a burst of white noise on the transmit data line; combining a tone signal with the burst; and sensing the burst to derive initial adapt filter coefficients.

Claim 12

Dependent Claim 72 words

A method as defined in claim 9 further comprising the preliminary steps of: defining a trip delay value for a delay from an output of the transmit data line to an input of the receive data line for a station loop line interface module; defining a first tap count for a number of taps for adaptation; and defining a second tap count for a number of taps for the subset for filtering.

Claim 13

Independent Claim 236 words

A method for providing echo cancellation signals in a hybrid in a voice messaging or voice response system having a memory store, a mass storage device and at least one digital signal processor providing a receive data line and a transmit data line and being coupled to the memory store and the mass storage device, the method comprising the steps of: coupling an adaptive finite impulse response filter to the receive data line and to the transmit data line and to the digital signal processor; identifying a successive plurality of data frames on the transmit data line meeting a power criteria test; storing the data frames in a buffer in the memory store; deriving a plurality of adapt filter coefficients from the successive plurality of data frames; selecting successive windowed quantities of taps from each of the adapt filter coefficients; identifying a best windowed quantity having the most signal energy of the selected successive windowed quantities; adjusting the adapt filter coefficients in response to differences between an output of the adaptive finite impulse response filter and a real echo signal on the receive data line; generating a delay value; transferring the delay value and a subset of the adapt filter coefficients corresponding to the best windowed quantity to a cancel filter; generating a cancel echo signal proportional to cancel filter coefficients in the memory store; and mixing the cancel echo signal with the real echo signal.

Claim 14

Independent Claim 236 words

A method for providing echo cancellation signals in a hybrid in a voice messaging or voice response system having a memory store, a mass storage device and at least one digital signal processor providing a receive data line and a transmit data line and being coupled to the memory store and the mass storage device, the method comprising the steps of: coupling an adaptive finite impulse response filter to the receive data line and to the transmit data line and to the digital signal processor; identifying a successive plurality of data frames on the transmit data line meeting a power criteria test; storing the data frames in a buffer in the memory store; deriving a plurality of adapt filter coefficients from the successive plurality of data frames; selecting successive windowed quantities of taps from each of the adapt filter coefficients; identifying a best windowed quantity having the most signal energy of the selected successive windowed quantities; adjusting the adapt filter coefficients in response to differences between an output of the adaptive finite impulse response filter and a real echo signal on the receive data line; generating a delay value; transferring the delay value and a subset of the adapt filter coefficients corresponding to the best windowed quantity to a cancel filter; generating a cancel echo signal proportional to cancel filter coefficients in the memory store; and mixing the cancel echo signal with the real echo signal.

Claim 15

Dependent Claim 100 words

A method as defined in claim 11 wherein the step of generating a cancel echo signal causes echo cancellation on an input signal on the receive line in real time and wherein the step of storing the data frames is preceded by the steps of: truncating each of a successive plurality of data frames into a plurality of frame segments; testing whether processing cycles of the digital signal processor are available for use and, if so, setting a value for a boolean variable; and causing further echo cancellation functions to be performed responsive to the value of the boolean variable.

Claim 16

Dependent Claim 52 words

A method as defined in claim 11 wherein the step of storing the data frames is preceded by testing whether processing cycles of the digital signal processor are available for use and, if so, setting a boolean variable and causing further echo cancellation functions responsive to the value of the boolean variable.

Claim 17

Dependent Claim 41 words

A method as defined in claim 11 further comprising the initial steps of: transmitting a burst of white noise on the transmit data line; combining a tone signal with the burst; and sensing the burst and deriving initial adapt filter coefficients.

Claim 18

Dependent Claim 71 words

A method as defined in claim 14 further comprising the steps of: defining a trip delay value for a delay from an output of the transmit data line to an input of the receive data line for a station loop line interface module; defining a first tap count for a number of taps for adaptation; and defining a second tap count for the number of taps for the subset for filtering.

Annuity Stage	Window Opens	Payment Deadline	Surcharge Period Until	Estimated Fee	Status
3.5 Years (Year 4)	1998-03-20	1998-09-19	1999-03-21	$2000.00	Window Closed / Lapsed
7.5 Years (Year 8)	2002-03-20	2002-09-19	2003-03-21	$3760.00	Window Closed / Lapsed
11.5 Years (Year 12)	2006-03-20	2006-09-19	2007-03-21	$7700.00	Window Closed / Lapsed

Adaptive echo canceller for voice messaging system

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