Pitch extraction methods and systems for speech coding using interpolation techniques

A method of searching for an interpolated time lag representative of an audio signal pitch period, the method using a correlation-based signal derived from an audio signal swd(n), the correlation-based signal having Np local peaks at corresponding known time lags kp(j), where j=1, 2, . . . Np, each of the Np local peaks being near a corresponding one of interpolated correlation-based peaks, each of the interpolated correlation-based peaks corresponding to an interpolated time lag, the method comprising:

• (a) determining if any of the time lags kp(j) are within a predetermined time lag range, the predetermined time lag range including a time lag representative of a past pitch period of a past portion of the audio signal;
• (b) comparing the interpolated peaks corresponding to the time lags determined to be within the predetermined time lag range;
• and
• (c) selecting the interpolated time lag corresponding to a largest interpolated peak among the interpolated peaks compared in step (b).

A computer readable medium carrying one or more sequences of one or more instructions for execution by one or more processors to perform a method of searching for an interpolated peak of a Normalized Correlation Square (NCS) signal derived from an audio signal, the NCS signal being represented as a first ratio of a correlation square signal c2(k) to an energy signal E(k), where k represents time lags spanning a range of integer k-values, the interpolated peak being near a known local peak c2(kp)/E(kp) of the NCS signal, the instructions when executed by the one or more processors, causing the one or more processors to perform the steps of:

• (a) producing quadratically interpolated correlation (QIC) signal values (ci) at interpolated time lags between time lag kp and an adjacent time lag;
• (b) squaring each of the QIC signal values to produce square QIC signal values (ci2);
• (c) producing an individual interpolated energy signal value (ei) corresponding to each of the square QIC signal values, wherein second ratios of the square QIC signal values (ci2) to their corresponding interpolated energy values (ei) represent interpolated NCS signal values;
• and
• (d) selecting, as the interpolated peak, a largest interpolated NCS signal value among the interpolated NCS signal values without evaluating the second ratios.

A computer readable medium carrying one or more sequences of one or more instructions for execution by one or more processors to perform a method of searching for an interpolated time lag representative of an audio signal pitch period, the method using a correlation-based signal derived from an audio signal swd(n), the correlation-based signal having Np local peaks at corresponding known time lags kp(j), where j=1, 2, . . . Np, each of the Np local peaks being near a corresponding one of interpolated correlation-based peaks, each of the interpolated correlation-based peaks corresponding to an interpolated time lag, the instructions when executed by the one or more processors, causing the one or more processors to perform the steps of:

• (a) determining if any of the time lags kp(j) are within a predetermined time lag range, the predetermined time lag range including a time lag representative of a past pitch period of a past portion of the audio signal;
• (b) comparing the interpolated peaks corresponding to the time lags determined to be within the predetermined time lag range;
• and
• (c) selecting the interpolated time lag corresponding to a largest interpolated peak among the interpolated peaks compared in step (b).

An apparatus for searching for an interpolated peak of a Normalized Correlation Square (NCS) signal derived from an audio signal, the NCS signal being represented as a first ratio of a correlation square signal c2(k) to an energy signal E(k), where k represents time lags spanning a range of integer k-values, the interpolated peak being near a known local peak c2(kp)/E(kp) of the NCS signal, comprising:

• a first module for
• producing quadratically interpolated correlation (QIC) signal values (ci) at interpolated time lags between time lag kp and an adjacent time lag, and
• squaring each of the QIC signal values to produce square QIC signal values (ci2);
• a second module for producing an individual interpolated energy signal value (ei) corresponding to each of the square QIC signal values, wherein second ratios of the square QIC signal values (ci2) to their corresponding interpolated energy values (ei) represent interpolated NCS signal values;
• and
• a third module for selecting, as the interpolated peak, a largest interpolated NCS signal value among the interpolated NCS signal values without evaluating the second ratios.

An apparatus for searching for an interpolated time lag representative of an audio signal pitch period, the method using a correlation-based signal derived from an audio signal swd(n), the correlation-based signal having Np local peaks at corresponding known time lags kp(j), where j=1, 2, . . . Np, each of the Np local peaks being near a corresponding one of interpolated correlation-based peaks, each of the interpolated correlation-based peaks corresponding to an interpolated time lag, comprising:

• a first module for determining if any of the time lags kp(j) are within a predetermined time lag range, the predetermined time lag range including a time lag representative of a past pitch period of a past portion of the audio signal;
• a second module for comparing the interpolated peaks corresponding to the time lags determined to be within the predetermined time lag range;
• and
• a third module for selecting the interpolated time lag corresponding to a largest interpolated peak among the interpolated peaks compared by the second module.