Low-complexity method for improving the performance of autocorrelation-based pitch detectors
First Claim
1. A method of operating an autocorrelation pitch detector for use in a vocoder comprising the steps of:
- tracking times of occurrence of a highest and a second-highest autocorrelation peak in an input signal;
comparing amplitudes of said highest and second-highest autocorrelation peaks;
identifying said times of occurrence to determine if the time position of said highest autocorrelation peak and the time position of said second-highest autocorrelation peak are in a predetermined ratio when said highest and second-highest autocorrelation peaks are within a predetermined percentage difference in amplitude; and
selecting as a true autocorrelation peak one of said highest or second-highest autocorrelation peaks when said predetermined ratio exists between said time position of said highest autocorrelation peak and said time position of said second-highest autocorrelation peak.
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Abstract
A method of operating an autocorrelation pitch detector for use in a vocoder overcomes the pitch doubling and tripling problem using a heuristic rather than an analytic approach. The process tracks the times of occurrence of a highest and a second-highest autocorrelation peak. The amplitudes of the highest and the second-highest autocorrelation peaks are compared and, when these peaks are within a predetermined percentage difference in amplitude, the ratio of the time position (IPITCH2) of the second-highest peak to the time position (IPITCH) of the highest peak is checked to determine if that ratio is 1/3, 1/2 or 2/3, within a predetermined error limit ε. If so and if the ratio is either 1/2 or 1/3, then IPITCH is set equal to IPITCH2 as reepresentative of the pitch period while, if the ratio is 2/3, then IPITCH is divided by three in order to represent the pitch period.
290 Citations
8 Claims
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1. A method of operating an autocorrelation pitch detector for use in a vocoder comprising the steps of:
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tracking times of occurrence of a highest and a second-highest autocorrelation peak in an input signal; comparing amplitudes of said highest and second-highest autocorrelation peaks; identifying said times of occurrence to determine if the time position of said highest autocorrelation peak and the time position of said second-highest autocorrelation peak are in a predetermined ratio when said highest and second-highest autocorrelation peaks are within a predetermined percentage difference in amplitude; and selecting as a true autocorrelation peak one of said highest or second-highest autocorrelation peaks when said predetermined ratio exists between said time position of said highest autocorrelation peak and said time position of said second-highest autocorrelation peak. - View Dependent Claims (2, 3, 4, 5)
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6. A method of operating an autocorrelation pitch detector for use in a vocoder comprising the steps of:
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tracking times of occurrence of a highest and a second-highest autocorrelation peak in an input signal; comparing amplitudes of said highest and second-highest autocorrelation peaks; checking said times of occurrence to determine if the ratio of the time position of said highest autocorrelation peak to the time position of said second-highest autocorrelation peak is approximately 3;
2 when said highest and second-highest autocorrelation peaks are within said predetermined percentage difference in amplitude; anddividing said time position of said highest autocorrelation peak by three when said 3;
2 ratio exists to provide a resulting output signal representing true pitch period.
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7. An autocorrelation pitch detector for use in a vocoder comprising:
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autocorrelation means for autocorrelating an input signal and generating an output signal having a plurality of peaks; first analyzer means for tracking times of occurrence of a highest and a second-highest autocorrelation peak from said autocorrelation means; and second analyzer means responsive to said first analyzer means for comparing amplitudes of said highest and second-highest autocorrelation peaks, checking said positions to determine if the ratio of the time position of said highest autocorrelation peak to the time position of said second-highest autocorrelation peak is approximately 2;
1 or 3;
1 when said highest and second-highest autocorrelation peaks are within a predetermined percentage difference in amplitude, and selecting as a true autocorrelation peak one of said highest or second-highest autocorrelation peaks when said approximately 2;
1 or 3;
1 ratio exists between said time position of said highest autocorrelation peak and said time position of said second-highest autocorrelation peak.
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8. An autocorrelation pitch detector for use in a vocoder comprising:
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autocorrelation means for autocorrelating an input signal and generating an output signal having a plurality of peaks; first analyzer means for tracking times of occurrence of a highest and a second-highest autocorrelation peak from said autocorrelation means; and second analyzer means responsive to said first analyzer means for comparing amplitudes of said highest and second-highest autocorrelation peaks, checking said positions to determine if the ratio of the time position of said highest autocorrelation peak to the time position of said second-highest autocorrelation peak is approximately 3;
2 when said highest and second-highest autocorrelation peaks are within said predetermined percentage difference in amplitude, and dividing said time position of said highest autocorrelation peak by three when said 3;
2 ratio exists to provide a resulting output signal representing true pitch period.
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Specification