Pitch detector and method thereof
First Claim
Patent Images
1. A pitch detector for extracting pitch information from an audio signal comprising:
- (a) low pass filter means coupled to receive the audio signal and for attenuating speech components in the audio signal generally higher than human pitch frequencies for producing a filtered audio signal; and
(b) DC shifting means coupled to said low pass filter means and to receive the audio signal for causing the pitch peaks of said filtered audio signal to be above a reference voltage such that crossovers of said reference voltage occur substantially at a rate of twice the pitch frequency.
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Abstract
A pitch and voiced/unvoiced detector comprising a low pass filter or variable cutoff frequency low pass filter for providing a constant power output, DC shifting and weighting circuits operating on the filtered analog signals, a summing circuit for the filtered and weighted signals, a peak detector with controlled exponential decay time and timing circuits which are used to distinguish pitch and voiced/unvoiced structure in the analog input signal.
19 Citations
26 Claims
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1. A pitch detector for extracting pitch information from an audio signal comprising:
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(a) low pass filter means coupled to receive the audio signal and for attenuating speech components in the audio signal generally higher than human pitch frequencies for producing a filtered audio signal; and (b) DC shifting means coupled to said low pass filter means and to receive the audio signal for causing the pitch peaks of said filtered audio signal to be above a reference voltage such that crossovers of said reference voltage occur substantially at a rate of twice the pitch frequency. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A pitch detector comprising:
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(a) low pass filter means having a double pole response in the region of 300 Hz for receiving and filtering an incoming audio signal thereby producing a filtered audio signal; (b) first full wave peak detector means coupled to said incoming audio signal and having a time constant substantially in the range of 1 to 2 seconds for averaging the peaks of said incoming audio signal; (c) second full wave peak detector means coupled to said low pass filter means and having a time constant substantially in the range of 5 to 20 milliseconds for averaging the peaks of said filtered audio signal; (d) summer means for summing said filtered audio signal, output of said first full wave peak detector means, and output of said second full wave peak detector means for producing a filtered audio frequency signal having excursions above a reference voltage equal in frequency to the pitch of said audio signal. - View Dependent Claims (8, 9, 10)
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11. A pitch detector comprising:
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(a) input amplitude adjustment means for receiving an audio signal and for producing a regulated audio signal having a constant average power; and (b) variable cutoff frequency low pass filter means coupled to said input amplitude adjustment means for extracting low frequency components of said audio signal which provide a fraction of said constant average power of said regulated audio signal, said low frequency components being substantially comprised of the pitch signal of said audio signal. - View Dependent Claims (12, 13, 14, 15, 16)
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17. A method of detecting the pitch frequency of an audio signal which comprises the steps of:
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(a) filtering the audio signal for attenuating high frequency components of the audio siignal and thereby producing a filtered audio signal; (b) DC shifting said filtered audio signal by an amount proportional to the peak values of the audio signal and said filtered audio signal so as to place the pitch peaks of said filtered audio siignal above a reference voltage such that crossovers of said reference voltage occur substantially at a rate of twice the pitch frequency.
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18. A method of detecting the input audio signal which comprises the steps of:
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(a) filtering the input audio signal with a low pass filter for attenuating frequencies greater than the highest anticipated pitch frequency for producing a filtered audio signal; (b) DC shifting the input audio signal by approximately six percent of the peak signal with a peak detector having an exponential decay time constant of two seconds for producing a first DC offset voltage; (c) DC shifting said filtered audio signal by approximately thirty percent of the peak signal with a peak detector having an exponential decay time constant substantially in the range of five to twenty millliseconds for producing a second DC offset voltage; (d) summing said filtered audio signal, said first DC offset voltage and said second DC offset voltage for producing a shifted audio signal so as to place the pitch peaks of said filtered audio signal above a reference voltage and substantially all other components of said filtered audio signal below said reference voltage. - View Dependent Claims (19, 20, 21)
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22. A method of detecting the pitch of an audio signal which comprises the steps of:
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(a) adjusting the amplitude of the audio signal to produce a constant average power audio signal; (b) low pass filtering said constant average power audio signal by varying the cuttoff frequency of a variable low pass filter for producing a filtered audio signal having a constant average power which is a fraction of the average power of said constant average power signal, said filtered audio signal substantially comprised of the pitch of the audio signal. - View Dependent Claims (23, 24, 25, 26)
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Specification