Electrolaryngeal speech enhancement for telephony

• US 6,975,984 B2
• Filed: 02/07/2001
• Issued: 12/13/2005
• Est. Priority Date: 02/08/2000
• Status: Expired due to Fees

• Current Assignee: Speech Technology and Applied Research Corporation
• Original Assignee: Speech Technology and Applied Research Corporation
• Inventors: Espy-Wilson, Carol, Chari, Venkatesh, MacAuslan, Joel M., Goldhor, Richard
• Primary Examiner(s): Young, W. R.
• Assistant Examiner(s): Wozniak, James S.
• Application Number:
  US09/778,675
• Publication Number:
  US 20010033652A1
• Time in Patent Office: 1,770 Days
• Field of Search: 704/208, 704/210, 704/219, 704/233, 704/226, 704/271, 381/70
• US Class Current: 704/208
• CPC Class Codes: G10L 2021/0135 Voice conversion or morphing
• CPC Class Codes: G10L 2025/783 based on threshold decision
• CPC Class Codes: G10L 2025/937 Signal energy in various frequency bands
• CPC Class Codes: G10L 25/93 Discriminating between voiced and unvoiced parts of speech signals G10L25/90 takes precedence

Abstract

A technique for separating an acoustic signal into a voiced (V) component corresponding to an electrolaryngeal source and an unvoiced (U) component corresponding to a turbulence source. The technique can be used to improve the quality of electrolaryngeal speech, and may be adapted for use in a special purpose telephone. A method according to the invention extracts a segment of consecutive values from the original stream of numerical values, and performs a discrete Fourier transform on the this first group of values. Next, a second group of values is extracted from components of the discrete Fourier transform result which correspond to an electrolaryngeal fixed repetition rate, F0, and harmonics thereof. An inverse-Fourier transform is applied to the second group of values, to produce a representation of a segment of the V component. Multiple V component segments are then concatenated to form a V component sample stream. Finally, the U component is determined by subtracting the V component sample stream from the original stream of numerical values.

Claims

1. A method for processing an acoustic signal to separate the acoustic signal into a voiced (V) component corresponding to an electrolaryngeal source and an unvoiced (U) component corresponding to a turbulence source, the method comprising the steps of:

digitizing the acoustic signal to produce an original stream of numerical values;

extracting a segment of consecutive values from the original stream of numerical values to produce a first group of values covering two or more periods of the electrolaryngeal source;

performing a discrete Fourier transform on the first group of values to produce a discrete Fourier transform result;

extracting a second group of values from components of the discrete Fourier transform result which correspond to an electrolaryngeal fixed repetition rate, F₀, and harmonics thereof;

inverse-Fourier transforming the second group of values, to produce a representation of a segment of the V component;

concatenating multiple V component segments to form a V component sample stream;

determining the U component by subtracting the V component sample stream from the original stream of numerical values;

determining segments of the input acoustic signal that correspond to inter-word segments;

filtering the V component sample stream;

for segments determined to be inter-word segments, setting the corresponding values of the V component sample stream to a zero value;

adding the U component values to the altered V component sample stream values; and

producing a processed acoustic sample stream from the addition of the U values and altered V values.

2. A method as in claim 1 wherein the step of determining inter-word segments includes a step of determining total power in the segments and characterizing such segments with relatively low power as inter-word segments.

3. A method as in claim 1 wherein the steps are performed in a digital signal processor connected in line with a telephone apparatus.

4. A method as in claim 1 wherein the step of determining inter-word segments further comprises:

determining an average power level for the group of values; and

if the average power level of the group of values is below a threshold value, determining that the group of values corresponds to an inter-word segment of the acoustic signal.

5. A method as in claim 4 additionally comprising the step of:

if the average power level of the group of values is above a threshold value, determining that the group of values corresponds to a non-inter-word segment of the acoustic signal.

6. A method for processing an acoustic signal to separate the acoustic signal into a voiced (V) component corresponding to an electrolaryngeal source and an unvoiced (U) component corresponding to a turbulence source, the method comprising the steps of:

digitizing the acoustic signal to produce an original stream of numerical values;

extracting a segment of consecutive values from the original stream of numerical values to produce a first group of values covering two or more periods of the electrolaryngeal source;

performing a discrete Fourier transform on the first group of values to produce a discrete Fourier transform result;

extracting a second group of values from components of the discrete Fourier transform result which correspond to an electrolaryngeal fixed repetition rate, F₀, and harmonics thereof;

inverse-Fourier transforming the second group of values, to produce a representation of a segment of the V component;

concatenating multiple V component segments to form a V component sample stream;

determining the U component by subtracting the V component sample stream from the original stream of numerical values;

filtering the V component sample stream;

setting corresponding selected values of the V component sample stream to a zero value;

adding the U component values to the altered V component sample stream values; and

producing a processed acoustic sample stream from the addition of the U values and altered V values.

7. A method as in claim 6 additionally comprising the step of:

setting the group of values to a zero value if they correspond to an inter-word segment.