Pitch extracting apparatus having means for measuring interval between zero-crossing points of a waveform

Claims

What is claimed is:

1. A pitch extracting apparatus comprising:

first interval measuring means for measuring an interval, as a first interval, between a zero-crossing point, at which an input waveform changes from a negative or positive first polarity to a second polarity, and a next zero-crossing point at which the input waveform changes from the second polarity to the first polarity;

second interval measuring means for, after measurement by said first interval measuring means is completed, sequentially measuring each interval, as a second interval, between each zero-crossing point, at which the input waveform changes from the first polarity to the second polarity, and a corresponding next zero-crossing point at which the input waveform changes from the second polarity to the first polarity;

third interval measuring means for sequentially measuring intervals from the zero-crossing point at which measurement by said first interval measuring means is started;

interval storage means for sequentially updating and storing the intervals, as period data, which are measured by said third interval measuring means at the respective points of time at which said second interval measuring means starts measuring the respective second intervals;

determining means for sequentially checking whether the first interval measured by said first interval measuring means is nearly equal to the respective second intervals sequentially measured by said second interval measuring means within a predetermined tolerance range; and

repetitive control means for outputting the period data stored in said interval storage means as pitch data of the input waveform at a point of time at which said determining means detects an equality where the measured first interval is nearly equal to said respective measured second intervals, and for sequentially extracting pitch data from the input data by sequentially repeating each processing from the measurement by said first interval measuring means.

2. An apparatus according to claim 1, further comprising control means for checking whether the interval measured by said third interval measuring means exceeds an interval corresponding to a pitch period of a predetermined lowest tone at a point of time at which the equality is not detected by said determining means, and for repeating each processing from the measurement by said first interval measuring means if it is determined that the interval exceeds the pitch period.

3. A pitch extracting apparatus comprising:

first interval measuring means for measuring an interval, as a first interval, between a zero-crossing point, at which an input waveform changes from a negative or positive first polarity to a second polarity, and a next zero-crossing point at which the input waveform changes from the second polarity to the first polarity;

first accumulated amplitude value measuring means for measuring an accumulated value of absolute amplitude values of the input waveform, as a first accumulated amplitude value, which said first interval measuring means is measuring the first interval;

second interval measuring means for, after measurement by said first interval measuring means is completed, sequentially measuring each interval, as a second interval, between each zero-crossing point, at which the input waveform changes from the first polarity to the second polarity, and a corresponding next zero-crossing point at which the input waveform changes from the second polarity to the first polarity;

second accumulated amplitude value measuring means for sequentially measuring an accumulated value of absolute amplitude values of the input waveform, as a second accumulated amplitude value, in the respective intervals in which said second interval measuring means sequentially measures the respective second intervals;

third interval measuring means for sequentially measuring intervals from the zero-crossing point at which measurement by said first interval measuring means is started;

interval storage means for sequentially updating and storing the intervals, as period data, which are measured by said third interval measuring means at the respective points of time at which said second interval measuring means starts measuring the respective second intervals;

determining means for sequentially checking whether the first interval measured by said first interval measuring means is nearly equal to the respective second intervals sequentially measured by said second interval measuring means within a predetermined tolerance range, and for sequentially checking whether the first accumulated amplitude value measured by said first accumulated amplitude value measuring means is nearly equal to the respective sound accumulated amplitude values sequentially measured by said second accumulated amplitude value measuring means within a predetermined tolerance range; and

repetitive control means for outputting the period data stored in said interval storage means as pitch data of the input waveform at a point of time at which said determining means detects an equality, representing that the first interval is nearly equal to one of the second intervals and that the first accumulated amplitude value is nearly equal to one of the second accumulated amplitude values and for sequentially extracting pitch data from the input data by sequentially repeating each processing from the measurement by said first interval measuring means.

4. An apparatus according to claim 3, further comprising control means for checking whether the interval measured by said third interval measuring means exceeds an interval corresponding to a pitch period of a predetermined lowest tone at a point of time at which the equality is not detected by said determining means, and for repeating each processing from the measurement by said first interval measuring means if it is determined that the interval exceeds the pitch period.

5. A pitch extracting apparatus comprising:

first interval measuring means for measuring an interval, as a first interval, between a zero-crossing point, at which an input waveform changes from a negative or positive first polarity to a second polarity, and a next zero-crossing point at which the input waveform changes from the second polarity to the first polarity;

first maximum amplitude value measuring means for measuring a maximum amplitude value of the input waveform, as a first maximum amplitude value, while said first interval measuring means is measuring the first interval;

second interval measuring means for, after measurement by said first interval measuring means is completed, sequentially measuring each interval, as a second interval, between each zero-crossing point, at which the input waveform changes from the first polarity to the second polarity, and a corresponding next zero-crossing point at which the input waveform changes from the second polarity to the first polarity;

second maximum amplitude value measuring means for sequentially measuring a maximum value of absolute amplitude values of the input waveform, as a second maximum amplitude value, in the respective intervals in which said second interval measuring means sequentially measures the respective second intervals;

third interval measuring means for sequentially measuring intervals from the zero-crossing point at which measurement by said first interval measuring means is started;

interval storage means for sequentially updating and storing the intervals, as period data, which are measured by said third interval measuring means at the respective points of time at which said second interval measuring means starts measuring the respective second intervals;

determining means for sequentially checking whether the first interval measured by said first interval measuring means is nearly equal to the respective second intervals sequentially measured by said second interval measuring means within a predetermined tolerance range, and for sequentially checking whether the first maximum amplitude value measured by said first maximum amplitude value measuring means is nearly equal to the respective second maximum amplitude values sequentially measured by said second maximum amplitude value measuring means within a predetermined tolerance range; and

repetitive control means for outputting the period data stored in said interval storage means as pitch data of the input waveform at a point of time at which said determining detects an equality representing that the first interval is nearly equal to one of the second intervals and that the first maximum amplitude value is nearly equal to one of the second maximum amplitude values, and for sequentially extracting pitch data from the input data by sequentially repeating each processing from the measurement by said first interval measuring means.

6. An apparatus according to claim 5, further comprising control means for checking whether the interval measured by said third interval measuring means exceeds an interval corresponding to a pitch period of a predetermined lowest tone at a point of time at which the equality is not detected by said determining means, and for repeating each processing from the measurement by said first interval measuring means if it is determined that the interval exceeds the pitch period.

7. A pitch extracting apparatus comprising:

means for receiving an input waveform signal;

measuring means for measuring time intervals between zero-crossing points of said input waveform signal;

detecting means for sequentially obtaining time intervals, of the time intervals between a plurality of zero-crossing points sequentially measured by said measuring means, which are defined by zero-crossing points having a first characteristic and next adjacent zero-crossing points having a second characteristic, and for detecting substantial coincidence between two time intervals;

pitch data output means for, when the substantial coincidence is detected by said detecting means, outputting a time interval between the zero-crossing points having the first characteristic and belonging to the two time intervals between which the substantial coincidence is detected, as pitch data;

waveform area calculating means for obtaining areas of waveform elements between consecutive zero-crossing points of the input waveform signal; and

waveform area coincidence detecting means for, when said detecting means sequentially obtains time intervals between zero-crossing points having the first characteristic and next adjacent zero-crossing points having the second characteristic, and detects substantial coincidence between two time intervals, detecting substantial coincidence between corresponding waveform areas obtained by said waveform area calculating means, and

wherein said pitch data output means comprises means for, only when said waveform area coincident detecting means detects the substantial coincidence between the corresponding waveform areas, outputting a time interval between the zero-crossing points having the first characteristic and belonging to the two time intervals between which the coincidence is detected, as pitch data.

8. A pitch extracting apparatus comprising:

means for receiving an input waveform signal;

measuring means for measuring time intervals between zero-crossing points of said input waveform signal;

detecting means for sequentially obtaining time intervals, of the time intervals between a plurality of zero-crossing points sequentially measured by said measuring means, which are defined by zero-crossing points having a first characteristic and next adjacent zero-crossing points having a second characteristic, and for detecting substantial coincidence between two time intervals;

pitch data output means for, when the substantial coincidence is detected by said detecting means, outputting a time interval between the zero-crossing points having the first characteristic and belonging to the two time intervals between which the substantial coincidence is detected, as pitch data;

waveform maximum value calculating means for obtaining maximum amplitude values of waveform elements between consecutive zero-crossing points of the input waveform signal; and

waveform maximum value coincidence detecting means for, when said detecting means sequentially obtains time intervals between zero-crossing points having the first characteristic and next adjacent zero-crossing points having the second characteristic, and detects substantial coincidence between two time intervals, detecting substantial coincidence between corresponding maximum amplitude values of waveform elements obtained by said waveform maximum value calculating means, and

wherein said pitch data output means comprises means for, only when said waveform maximum value coincidence detecting means detects the substantial coincidence between the corresponding maximum values of the waveform elements, outputting a time interval between the zero-crossing points having the first characteristic and belonging to the two time intervals between which the coincidence is detected, as pitch data.

9. A pitch extracting method comprising:

a first step of measuring an interval, as a first interval, between a zero-crossing point, at which an input waveform changes from a negative or positive first polarity to a second polarity, and a next zero-crossing point at which the input waveform changes from the second polarity to the first polarity;

a second step of sequentially measuring, after measurement in said first step is completed, each interval, as a second interval, between each zero-crossing point at which the input waveform changes from the first polarity to the second polarity, and a corresponding next zero-crossing point at which the input waveform changes from the second polarity to the first polarity;

a third step of sequentially measuring intervals from the zero-crossing point at which measurement in said first step is started;

a fourth step of sequentially updating and storing the intervals, as period data, which are measured in said third step at the respective points of time at which measuring of the respective second intervals is started in said second step;

a fifth step of detecting an equality by sequentially checking whether the first interval measured in said first is nearly equal to the respective second intervals sequentially measured in said second step within a predetermined tolerance range; and

a sixth step of outputting the period data stored in said fourth step as pitch data of the input waveform at a point of time at which said equality is detected in said fifth step, said equality being when said first interval is determined to be nearly equal to the respective second intervals, and the sequentially extracting pitch data from the input data by sequentially repeating each processing from the measurement in said first step.

10. A method according to claim 9, further comprising checking whether the interval measured in said third step exceeds an interval corresponding to a pitch period of a predetermined lowest tone at a point of time at which the equality is not detected said fifth step, and repeating each processing from the measurement in said first step if it is determined that the interval exceeds the pitch period.

11. A pitch extracting method comprising:

a first step of measuring an interval, as a first interval, between a zero-crossing point, at which an input waveform changes from a negative or positive first polarity to a second polarity, and a next zero-crossing point at which the input waveform changes from the second polarity to the first polarity;

measuring an accumulated value of absolute amplitude values of the input waveform, as a first accumulated amplitude value, while said first interval is being measured;

a second step of sequentially measuring, after measurement in said first step is completed, each interval, as a second interval, between each zero-crossing point, at which the input waveform changes from the first polarity to the second polarity, and a corresponding next zero-crossing point at which the input waveform changes from the second polarity to the first polarity;

sequentially measuring an accumulated value of absolute amplitude values of the input waveform, as a second accumulated amplitude value, in the respective intervals in which said second intervals are being measured in said second step;

a third step of sequentially measuring intervals from the zero-crossing point at which measurement in said first step is started;

sequentially updating and storing the intervals in an interval storage means, as period data, which are measured in said third step at the respective points of time at which said second intervals are started to be measured in said second step;

sequentially checking whether the first interval measured in said first step is nearly equal to the respective second intervals sequentially measured in said second step within a predetermined tolerance range, and sequentially checking whether the first accumulated amplitude value is nearly equal to the respective seqentially measured second accumulated amplitude values within a predetermined tolerance range; and

outputting the period data stored in said interval storage means as pitch data of the input waveform at a point of time at which an equality is detected in said sequentially checking step which represents that the first interval is nearly equal to one of the second intervals and that the first accumulated amplitude value is nearly equal to one of the second accumulated amplitude values, and then sequentially extracting pitch data from the input data by sequentially repeating each processing beginning from the measurement of said first interval.

12. A method according to claim 11, further comprising checking whether the interval measured in said third step exceeds an interval corresponding to a pitch period of a predetermined lowest tone at a point of time at which the equality is not detected in said sequentially checking step, and repeating each processing beginning from the measurement of said first interval if it is determined that the interval exceeds the pitch period.

13. A pitch extracting method comprising:

a first step of measuring an interval, as a first interval, between a zero-crossing point, at which an input waveform changes from a negative or positive first polarity to a second polarity, and a next zero-crossing point at which the input waveform changes from the second polarity to the first polarity;

measuring a maximum amplitude value of the input waveform, as a first maximum amplitude value, while said first interval is being measured;

a second step of sequentially measuring, after measurement in said first step is completed, each interval, as a second interval, between each zero-crossing point, at which the input waveform changes from the first polarity to the second polarity, and a corresponding next zero-crossing point at which the input waveform changes from the second polarity to the first polarity;

sequentially measuring a maximum value of absolute amplitude values of the input waveform, as a second maximum amplitude value, in the respective intervals in which said second intervals are being measured in said second step;

a third step of sequentially measuring intervals from the zero-crossing point at which measurement in said first step is started;

sequentially updating and storing the intervals in an interval storage means, as period data, which are measured in said third step at the respective points of time at which said second intervals are started to be measured in said second step;

sequentially checking whether the first interval measured in said first step is nearly equal to the respective second intervals sequentially measured in said second step within a predetermined tolerance range, and sequentially checking whether the first maximum amplitude value is nearly equal to the respective sequentially measured second maximum amplitude values within a predetermined tolerance range; and

outputting the period data stored in said interval storage means as pitch data of the input waveform at a point of time at which an equality is detected in said sequentially checking step which represents that the first interval is nearly equal to one of the second intervals and that the first maximum amplitude value is nearly equal to one of the second maximum amplitude values, and then sequentially extracting pitch data from the input data by sequentially repeating each processing beginning from the measurement of said first interval.

14. A method according to claim 13, further comprising checking whether the interval measured in said third step exceeds an interval corresponding to a pitch period of a predetermined lowest tone at a point of time at which the equality is not detected in said sequentially checking step, and for repeating each processing beginning from the measurement of said first interval if it is determined that the interval exceeds the pitch period.

15. A pitch extracting method comprising:

a step of receiving an input waveform signal;

a step of measuring time intervals between zero-crossing points of said input waveform signal;

a detecting step of sequentially obtaining time intervals, of the time intervals between a plurality of zero-crossing points sequentially measured in said measuring step, which are defined by zero-crossing points having a first characteristic and next adjacent zero-crossing points having a second characteristic, and detecting substantial coincidence between two time intervals;

a step of outputting, when the substantial coincidence is detected in said detecting step, a time interval between the zero-crossing points having the first characteristic and belonging to the two time intervals between which the coincidence is detected, as pitch data when said substantial coincidence is detected in said detecting step;

a step of obtaining areas of waveform elements between consecutive zero-crossing points of the input waveform signal; and

a step of determining when said detecting step sequentially obtains time intervals between zero-crossing points having the first characteristic and next adjacent zero-crossing points having the second characteristic, and when said detecting step detects substantial coincidence between two time intervals, and thereafter detecting substantial coincidence between corresponding waveform areas obtained in said obtaining step, and

wherein said outputting step further comprises outputting, only when said substantial coincidence between the corresponding waveform areas is detected in said determining step, a time interval between the zero-crossing points having the first characteristic and belonging to the two time intervals between which the coincidence is detected, as pitch data.

16. A pitch extracting method comprising:

a step of receiving an input waveform signal;

a step of measuring time intervals between zero-crossing points of said input waveform signal;

a detecting step of sequentially obtaining time intervals, of the time intervals between a plurality of zero-crossing points sequentially measured in said measuring step, which are defined by zero-crossing points having a first characteristic and next adjacent zero-crossing points having a second characteristic, and detecting substantial coincidence between two time intervals;

a step of outputting, when the substantial coincidence is detected in said detecting step, a time interval between the zero-crossing points having the first characteristic and belonging to the two time intervals between which the coincidence is detected, as pitch data when said substantial coincidence is detected in said detecting step;

a step of obtaining maximum amplitude values of waveform elements between consecutive zero-crossing points of the input waveform signal; and

a step of determining when said detecting step sequentially obtains time intervals between zero-crossing points having the first characteristic and next adjacent zero-crossing points having the second characteristic, and when said detecting step detects substantial coincidence between two time intervals, and thereafter detecting substantial coincidence between corresponding maximum amplitude values of waveform elements obtained in said obtained step, and

wherein said outputting step further comprises outputting, only when said substantial coincidence between the corresponding maximum values of the waveform elements is detected in said determining step, a time interval between the zero-crossing points having the first characteristic and belonging to the two time intervals between which the coincidence is detected, as pitch data.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pitch extracting apparatus for extracting a pitch (tone pitch) of the waveform of an input waveform signal.

2. Description of the Related Art

There have been strong demands for extraction of a pitch frequency or pitch period (to be simply referred to as a pitch hereinafter) of a musical tone signal consisting of a repetitive waveform, e.g., a singing voice of a person or a musical tone picked up by a microphone. If a pitch can be extracted, the extracted pitch data can be used for various types of processing. For example, a musical tone corresponding to the pitch (tone pitch) can be generated by an electronic musical instrument or the like.

Various methods have been proposed to extract pitches from audio signals. Of such conventional methods, a method of directly extracting a pitch from an audio signal in a time zone requires only a small amount of arithmetic operations and hence easily allows real-time processing.

According to a first conventional method of extracting a pitch in a time zone, the time interval between adjacent zero-crossing points (time positions at which the amplitude becomes zero) of an input waveform is obtained as the pitch period of the waveform.

According to a second conventional method, a zero-crossing interval is extracted after an input waveform is filtered by a low-pass filter to remove its harmonic components (see, e.g., U.S. Pat. No. 4,688,464 and U.S. Pat. No. 5,018,428).

In addition, according to a third conventional method, the auto-correlation values of an input waveform are calculated, and a pitch period is extracted on the basis of an auto-correlation deviation as a peak value (see, e.g., U.S. Pat. No. 4,633,748).

A human voice, however, contains a considerable amount of harmonic components, and hence a zero-crossing point appears several times within one pitch period of an input waveform. For this reason, if a zero-crossing interval is simply extracted as in the first conventional method, a correct period cannot be obtained, resulting in a large pitch extraction error.

In the second conventional method, if the cutoff frequency of the low-pass filter is decreased, the range in which a pitch can be extracted is limited to a small range of pitch. In contrast to this, if the cutoff frequency is increased, harmonic components are left to increase the pitch extraction error.

Furthermore, in the third conventional method, an enormous amount of arithmetic operations is required in spite of processing in a time zone. If, therefore, arithmetic operations are to be executed with high precision, the pitch of an input waveform cannot be extracted in real-time.

SUMMARY OF THE INVENTION

It is an object of the present invention to eliminate the influence of zero crossing caused by harmonic components described above, thereby allowing correct measurement of the zero-crossing interval, of an input waveform, which corresponds to one pitch period.

According to an arrangement of the present invention, an apparatus includes first interval measuring means for measuring an interval, as a first interval, between a zero-crossing point, at which an input waveform changes from a negative or positive first polarity to a second polarity, and a next zero-crossing point at which the input waveform changes from the second polarity to the first polarity.

The apparatus further includes second interval measuring means for, after measurement by the first interval measuring means is completed, sequentially measuring each interval, as a second interval, between each zero-crossing point, at which the input waveform changes from the first polarity to the second polarity, and a corresponding next zero-crossing point at which the input waveform changes from the second polarity to the first polarity.

The apparatus further includes third interval measuring means for sequentially measuring intervals between the zero-crossing point at which measurement by the first interval measuring means is started and predetermined respective points of time.

For example, the first, second, and third interval measuring means are constituted by counters.

The apparatus further includes interval storage means for sequentially updating and storing the intervals, as period data, which are measured by the third interval measuring means at the respective points of time at which the second interval measuring means starts measuring the respective second intervals.

The apparatus further includes determining means for sequentially checking whether the first interval measured by the first interval measuring means is nearly equal to the respective second intervals sequentially measured by the second interval measuring means within a predetermined tolerance range.

The apparatus further includes repetitive control means for outputting the period data stored in the interval storage means as pitch data of the input waveform at a point of time at which the determining means detects the coincidence, and sequentially extracting pitch data from the input data by sequentially repeating each processing from the measurement by the first interval measuring means.

According to the above-described arrangement of the present invention, the apparatus can be designed to have control means for checking whether the interval measured by the third interval measuring means exceeds an interval corresponding to a pitch period of a predetermined lowest tone at a point of time at which the equality is not detected by the determining means, and for repeating each processing from the measurement by the first interval measuring means if it is determined that the interval exceeds the pitch period.

A voice or speech signal is formed as a waveform having one or more peaks repeatedly appearing at every pitch period. The waveforms in consecutive pitch periods are similar in shape to each other. The intervals between the start and end zero-crossing points of substantially similar waveform elements in adjacent pitch periods are substantially equal to each other.

According to the present invention, in consideration of such characteristics, the first interval measuring means measures the interval between the zero-crossing points at the two ends of one waveform element, and the second interval measuring means subsequently measures the interval between the zero-crossing points at the two ends of each of subsequent waveform elements.

The determining means sequentially checks equality between the first interval and each second interval within the predetermined tolerance range, and extracts the interval between the start point of the waveform element corresponding to the first interval and the start point of the waveform element corresponding to the second interval at the point of time at which the equality is detected, as pitch data. This pitch data can be obtained as period data equivalent to each interval measured by the third measuring means and stored in the interval storage means.

With this operation, the pitch of an input waveform can be stably extracted regardless of the influence of harmonic components.

According to another arrangement of the present invention, an apparatus includes first interval measuring means for measuring an interval, as a first interval, between a zero-crossing point, at which an input waveform changes from a negative or positive first polarity to a second polarity, and a next zero-crossing point at which the input waveform changes from the second polarity to the first polarity.

The apparatus further includes first accumulated amplitude value measuring means for measuring an accumulated value of absolute amplitude values of the input waveform, as a first accumulated amplitude value, while the first interval measuring means is measuring the first interval.

The apparatus further includes second interval measuring means for, after measurement by the first interval measuring means is completed, sequentially measuring each interval, as a second interval, between each zero-crossing point, at which the input waveform changes from the first polarity to the second polarity, and a corresponding next zero-crossing point at which the input waveform changes from the second polarity to the first polarity.

The apparatus further includes second accumulated amplitude value measuring means for sequentially measuring accumulated values of absolute amplitude values of the input waveform, as a second accumulated amplitude value, in the respective intervals in which the second interval measuring means sequentially measures the respective second intervals.

The apparatus further includes third interval measuring means for sequentially measuring intervals between the zero-crossing point at which measurement by the first interval measuring means is started and predetermined respective points of time.

For example, the first, second, and third interval measuring means comprise by counters.

The apparatus further includes interval storage means for sequentially updating and storing the intervals, as period data, which are measured by the third interval measuring means at the respective points of time at which the second interval measuring means starts measuring the respective second intervals.

The apparatus further includes determining means for sequentially checking whether the first interval measured by the first interval measuring means is nearly equal to the respective second intervals sequentially measured by the second interval measuring means within a predetermined tolerance range, and sequentially checking whether the first accumulated amplitude value measured by the first accumulated amplitude value measuring means is nearly equal to the respective second accumulated amplitude values sequentially measured by the second accumulated amplitude value measuring means within a predetermined tolerance range.

The apparatus further includes repetitive control means for outputting the period data stored in the interval storage means as pitch data of the input waveform at a point of time at which the determining means detects the equality, and sequentially extracting pitch data from the input data by sequentially repeating each processing from the measurement by the first interval measuring means.

According to the above-described arrangement of the present invention, the apparatus can be designed to have control means for checking whether the interval measured by the third interval measuring means exceeds an interval corresponding to a pitch period of a predetermined lowest tone at a point of time at which the equality is not detected by the determining means, and for repeating each processing from the measurement by the first interval measuring means if it is determined that the interval exceeds the pitch period.

A voice signal is formed as a waveform having one or more peaks repeatedly appearing at every pitch period. The waveforms in consecutive pitch periods are similar in shape to each other. The intervals between the start and end zero-crossing points of substantially similar waveform elements and areas of the elements in adjacent pitch periods are substantially equal to each other.

According to the present invention, in consideration of such characteristics, the first interval measuring means measures the interval between the zero-crossing points at the two ends of one waveform element, and the first accumulated amplitude value measuring means measures a first accumulated amplitude value corresponding to the area of the waveform element. The second interval measuring means subsequently measures the interval between the zero-crossing points at the two ends of each of subsequent waveform elements, and the second accumulated amplitude value measuring means measures a second accumulated amplitude value corresponding to the area of each waveform element.

The determining means sequentially checks equality between the first interval and each second interval within the predetermined tolerance range, and between the first accumulated amplitude value and each second accumulated amplitude value with the predetermined tolerance range, and extracts the interval between the start point of the waveform element corresponding to the first interval and the start point of the waveform element corresponding to the second interval at the point of time at which the equality is detected, as pitch data. This pitch data can be obtained as period data equivalent to each interval measured by the third measuring means and stored in the interval storage means.

With this operation, the pitch of an input waveform can be stably extracted regardless of the influence of harmonic components.

According to still another arrangement of the present invention, an apparatus includes first interval measuring means for measuring an interval, as a first interval, between a zero-crossing point, at which an input waveform changes from a negative or positive first polarity to a second polarity, and a next zero-crossing point at which the input waveform changes from the second polarity to the first polarity.

The apparatus further includes first maximum amplitude value measuring means for measuring an absolute maximum amplitude value of the input waveform, as a first maximum amplitude value, while said first interval measuring means is measuring the first interval.

The apparatus further includes second interval measuring means for, after measurement by the first interval measuring means is completed, sequentially measuring each interval, as a second interval, between each zero-crossing point, at which the input waveform changes from the first polarity to the second polarity, and a corresponding next zero-crossing point at which the input waveform changes from the second polarity to the first polarity.

The apparatus further includes second maximum amplitude value measuring means for sequentially measuring maximum values of absolute amplitude values of the input waveform, as a second maximum amplitude value, in the respective intervals in which the second interval measuring means sequentially measures the respective second intervals.

The apparatus further includes third interval measuring means for sequentially measuring intervals from the zero-crossing point at which measurement by the first interval measuring means is started to a predetermined point of time.

For example, the first, second, and third interval measuring means comprise by counters.

The apparatus further includes interval storage means for sequentially updating and storing the intervals, as period data, which are measured by the third interval measuring means at the respective points of time at which the second interval measuring means starts measuring the respective second intervals.

The apparatus further includes determining means for sequentially checking whether the first interval measured by the first interval measuring means is nearly equal to the respective second intervals sequentially measured by the second interval measuring means within a predetermined tolerance range, and sequentially checking whether the first maximum amplitude value measured by the first maximum amplitude value measuring means is nearly equal to the respective second maximum amplitude values sequentially measured by the second maximum amplitude value measuring means within a predetermined tolerance range.

The apparatus further includes repetitive control means for outputting the period data stored in the interval storage means as pitch data of the input waveform at a point of time at which the determining means detects the equality, and sequentially extracting pitch data from the input data by sequentially repeating each processing from the measurement by the first interval measuring means.

According to the above-described arrangement of the present invention, the apparatus can be designed to