# US 7,610,196 B2 · Periodic signal enhancement system

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- Number: US 7,610,196 B2
- Document ID: US7610196B2
- Status: Granted
- Kind: B2
- Application number: 11/102,251
- Filed: 2005-04-08
- Published: 2006-04-27
- Granted: 2009-10-27
- Earliest claimed: 2004-10-26
- Assignees: QNX Software Systems (Wavemakers), Inc.
- Inventors: Rajeev Nongpiur; David Giesbrecht; Phillip Hetherington
- Web page: https://patentgrep.com/patent/US7610196B2

## CPC

- G10L 21/0364: for improving intelligibility
- G10L 25/90: Pitch determination of speech signals
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING

## Abstract

A signal enhancement system improves the understandability of speech or other audio signals. The system reinforces selected parts of the signal, may attenuate selected parts of the signal, and may increase SNR. The system includes delay logic, a partitioned adaptive filter, and signal reinforcement logic. The partitioned adaptive filter may track and enhance the fundamental frequency and harmonics in the input signal. The partitioned filter output signals may approximately reproduce the input signal, delayed by an integer multiple of the period of the fundamental frequency of the input signal. The reinforcement logic combines the input signal and the filtered signals to produce an enhanced output signal.

## Claims

### Claim 1

A signal enhancement system comprising:
a signal input;
partitioned delay logic coupled to the signal input;
a partitioned adaptive filter coupled to the partitioned delay logic and comprising multiple adaptive filter outputs;
filter reinforcement logic coupled to the adaptive filter outputs;
gain logic coupled to the filter reinforcement logic; and
signal reinforcement logic comprising circuitry, program instructions stored in memory, or both, where the signal reinforcement logic is coupled to the signal input and the gain logic and comprising an enhanced signal output.

### Claim 2 (depends on 1)

The signal enhancement system of claim 1, where the multiple filter outputs comprise a first filter output and a second filter output, and where the partitioned adaptive filter comprises:
a first adaptive filter comprising:
first filter coefficients;
the first filter output; and
a first error output;
a second adaptive filter comprising:
second filter coefficients;
the second filter output; and
a second error output,
wherein the first filter coefficients are adapted based on the first error output and the second filter coefficients are adapted based on the second error output.

### Claim 3 (depends on 2)

The signal enhancement system of claim 2, where the first error output comprises a first difference between the signal input and the first filter output, and where the second error output comprises a second difference between the signal input and the second filter output.

### Claim 4 (depends on 2)

The signal enhancement system of claim 2, where delay logic comprises an M1 sample delay coupled to the first adaptive filter and an M2 sample delay coupled to the second adaptive filter.

### Claim 5 (depends on 4)

The signal enhancement system of claim 4, where the M2 sample delay is in series with the M1 sample delay.

### Claim 6 (depends on 4)

The signal enhancement system of claim 4, where the first adaptive filter is a length M1 adaptive filter and where the second adaptive filter is a length M2 adaptive filter.

### Claim 7 (depends on 6)

The signal enhancement system of claim 6, where M1=M2.

### Claim 8 (depends on 6)

The signal enhancement system of claim 6, where M1=M2=1.

### Claim 9 (depends on 4)

The signal enhancement system of claim 4, where the first filter has a length smaller than M1 or the second filter has a length smaller than M2.

### Claim 10 (depends on 4)

The signal enhancement system of claim 4, where the first filter has a length greater than M1 or the second filter has a length greater than M2.

### Claim 11 (depends on 1)

The signal enhancement system of claim 1, where the delay logic comprises a D sample delay selected to set a maximum adaptation pitch.

### Claim 12 (depends on 1)

The signal enhancement system of claim 1, where the delay logic comprises an L sample delay selected to set an adaptation pitch range.

### Claim 13 (depends on 1)

The signal enhancement system of claim 1, where the delay logic implements an adaptation pitch range including a human voice pitch.

### Claim 14 (depends on 1)

The system of claim 1, where the delay logic implements an adaptation pitch range between approximately 70 Hz and approximately 400 Hz.

### Claim 15 (depends on 1)

The system of claim 1, further comprising a first stage filter comprising quasi-stationary frequency tracking and attenuation logic, where the first stage filter is coupled between the signal input and to the delay logic.

### Claim 16 (depends on 1)

The signal enhancement system of claim 1, where the signal reinforcement logic adds an output of the gain logic to a signal received at the signal input to generate an enhanced signal output with reinforced periodic signal content.

### Claim 17

A signal enhancement system comprising:
means for receiving an input signal;
means for delaying the input signal by multiple different delays;
means for partitioned adaptive filtering the input signal based on the multiple different delays; and
means for reinforcing the input signal with a partitioned adaptive filtering output.

### Claim 18 (depends on 17)

The signal enhancement system of claim 17, further comprising:
means for tracking and filtering a quasi-stationary signal in the input signal prior to filtering the input signal.

### Claim 19 (depends on 17)

The signal enhancement system of claim 17, further comprising means for adapting the means for partitioned adaptive filtering based on multiple error signals.

### Claim 20 (depends on 17)

The signal enhancement system of claim 17, further comprising:
means for biasing the partitioned adaptive filtering output.

### Claim 21 (depends on 17)

The signal enhancement system of claim 17, where the means for reinforcing comprises means for adding the partitioned adaptive filtering output to the input signal to generate an enhanced signal output with reinforced periodic signal content.

### Claim 22

A signal enhancement system comprising:
a signal input;
an M1 sample delay coupled to the signal input;
an M2 sample delay coupled to the M1 sample delay;
a first adaptive filter coupled to the M1 sample delay and comprising a first filter output;
a second adaptive filter coupled to the M2 sample delay and comprising a second filter output;
filter reinforcement logic connected to the first filter output and the second filter output; and
signal reinforcement logic comprising circuitry, program instructions stored in memory, or both, where the signal reinforcement logic is connected to the signal input and the filter reinforcement logic.

### Claim 23 (depends on 22)

The signal enhancement system of claim 22, where M1=M2.

### Claim 24 (depends on 22)

The signal enhancement system of claim 22, where M1=M2=1.

### Claim 25 (depends on 22)

The signal enhancement system of claim 22, further comprising an initial D sample delay coupled to the M1 sample delay, where ‘D’ is chosen to set a maximum adaptation pitch.

### Claim 26 (depends on 25)

The signal enhancement system of claim 25 where the D sample delay, the M1 sample delay, and the M2 sample delay implement an adaptation pitch range including that of human voice.

### Claim 27 (depends on 25)

The signal enhancement system of claim 25 where the D sample delay, the M1 sample delay, and the M2 sample delay implement an adaptation pitch range between approximately 70 Hz and approximately 400 Hz.

### Claim 28 (depends on 22)

The signal enhancement system of claim 22, further comprising a gain logic coupled to the filter reinforcement logic.

### Claim 29 (depends on 22)

The signal enhancement system of claim 22, further comprising a slowly adapting first stage filter coupled to the signal input.

### Claim 30 (depends on 29)

The signal enhancement system of claim 29, where the first stage filter comprises quasi-stationary signal tracking and attenuation logic.

### Claim 31 (depends on 22)

The signal enhancement system of claim 22, where the first adaptive filter comprises a first error output based on the input signal and the first filter output, and where the first adaptive filter comprises first coefficients adapted based on the first error output.

### Claim 32 (depends on 31)

The signal enhancement system of claim 31, where the second adaptive filter comprises a second error output based on the input signal and the second filter output, and where the second adaptive filter comprises second coefficients adapted based on the second error output.

### Claim 33 (depends on 22)

The signal enhancement system of claim 22, where the signal reinforcement logic adds the first filter output and the second filter output to a signal received at the signal input to generate an enhanced signal output with reinforced periodic signal content.

### Claim 34

A method for enhancing a signal, comprising:
receiving an input signal comprising a fundamental frequency;
delaying the input signal by multiple different sample delays to obtain multiple differently delayed input signals;
applying a partitioned adaptive filter comprising multiple individual adaptive filters to the multiple differently delayed input signals;
generating a filtered output with the partitioned adaptive filter, the filtered output approximately delayed by an integer multiple of the fundamental frequency;
generating an error signal for each of the multiple individual adaptive filters;
adapting each of the individual adaptive filters based on the error signal for that individual adaptive filter; and
reinforcing the input signal with the filtered output.

### Claim 35 (depends on 34)

The method of claim 34, further comprising:
forming a sum of outputs of the multiple adaptive filters;
biasing the sum by a gain parameter.

### Claim 36 (depends on 34)

The method of claim 34, further comprising:
determining a maximum pitch to track;
and where delaying the input signal comprises delaying the input signal by D samples, where D is selected according to the maximum pitch.

### Claim 37 (depends on 36)

The method of claim 36, further comprising:
selecting a pitch tracking range;
and where delaying the input signal comprises delaying the input signal by D+L samples, where L is selected to set the pitch tracking range.

### Claim 38 (depends on 37)

The method of claim 37, where the pitch range includes a human voice pitch.

### Claim 39 (depends on 37)

The method of claim 37, where the pitch range extends between approximately 70 Hz and approximately 400 Hz.

### Claim 40 (depends on 34)

The method of claim 34, where reinforcing comprises adding the filtered output to the input signal to generate an enhanced signal output with reinforced periodic signal content.

### Claim 41

A product comprising:
a machine readable medium; and
machine readable instructions embodied on the machine readable medium that:
delay an input signal comprising a fundamental frequency by multiple sample delays to obtain multiple differently delayed input signals;
apply a partitioned adaptive filter comprising multiple individual adaptive filters to the multiple delayed input signals;
generate a filtered output with the partitioned adaptive filter, the filtered output approximately delayed by an integer multiple of the fundamental frequency; and
reinforce the input signal with the output estimate.

### Claim 42 (depends on 41)

The product of claim 41, where the machine readable instructions further:
generate an error signal for each of the multiple individual adaptive filters; and
adapt each of the individual adaptive filters based on the error signal for that individual adaptive filter.

### Claim 43 (depends on 42)

The product of claim 42, where the delay instructions comprise:
D sample delay instructions, where D is selected to implement a maximum adaptation pitch for the multiple adaptive filters.

### Claim 44 (depends on 43)

The product of claim 43, where the delay instructions further comprise:
L sample delay instructions, where L is selected to implement a pitch tracking range for the multiple adaptive filters.

### Claim 45 (depends on 44)

The product of claim 44, where the pitch tracking range includes a human voice pitch.

### Claim 46 (depends on 44)

The product of claim 44, where the L sample delay instructions implement ‘i’ series connected sample delay blocks, each of equal length.

### Claim 47 (depends on 44)

The product of claim 44, where the L sample delay instructions implement ‘i’ series connected sample delay blocks, where at least two of the sample delay blocks have different lengths.

### Claim 48 (depends on 41)

The product of claim 41, where the machine readable instructions further:
bias the estimated fundamental frequency output by a gain parameter.

### Claim 49 (depends on 48)

The product of claim 48, where the gain parameter decreases with increasing signal-to-noise ratio.

### Claim 50 (depends on 48)

The product of claim 48, where the gain parameter increases with decreasing signal-to-noise ratio.

### Claim 51 (depends on 41)

The product of claim 41, where each of the multiple individual adaptive filters has a filter length of 1.

### Claim 52 (depends on 41)

The product of claim 41, where the reinforce instructions comprise instructions that add the filtered output to the input signal to generate an enhanced signal output with reinforced periodic signal content.