Sound analyzing apparatus

• US 4,075,423 A
• Filed: 04/14/1977
• Issued: 02/21/1978
• Est. Priority Date: 04/30/1976
• Status: Expired due to Term

• Current Assignee: International Computers Limited (Fujitsu Limited)
• Original Assignee: International Computers Limited (Fujitsu Limited)
• Inventors: Martin, Michael Joseph, Underwood, Michael John
• Primary Examiner(s): Claffy, Kathleen H.
• Assistant Examiner(s): Kemeny, E. S.
• Application Number:
  US05/787,448
• Time in Patent Office: 313 Days
• Field of Search: 179/1 SC, 179/1 SA, 179/1 P, 340/146.3 S, 235/92 PC
• US Class Current: 704/209
• CPC Class Codes: G10L 25/00 Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00 muting semiconductor-based amplifiers when some special characteristics of a signal are sensed by a speech detector, e.g. sensing when no signal is present, H03G3/34

Abstract

Sound Analyzing Apparatus is described for extracting from a speech signal certain basic formant waveforms present in the signal and then examining the formant waveforms to identify the frequency components of the waveforms, using a histogram format in a digital processor. This frequency analysis is accomplished by rectifying the formant waveform, detecting the occurrence of peaks in the resultant waveform and evaluating the time intervals between successive peaks. The apparatus is also biased to reject as invalid those time intervals when peaks of less than a predetermined magnitude occur. Since the formant waveform is typically a succession of damped waves, the frequencies detected are classified into ranges and a running average of the allocation of the frequency components over the ranges is developed over successive sampling periods in order to provide a histogram output illustrative of the final analysis.

Claims

1. Sound analysing apparatus for the evaluation of speech including means for extracting from an applied speech signal a required formant waveform;

means for identifying frequency components of the required formant in the waveform;

a first store having a plurality of addressable storage locations each associated respectively with a different predetermined range of frequencies;

means for adding during each of a succession of predetermined histogram sampling periods of value of unity for each frequency component identified into that one of the storage locations corresponding to the range in which lies the frequency of the identified component and means for producing over a histogram evaluation period comprising a plurality of sampling periods a histogram representation including means for scanning the storage locations in order, to produce for each successive sampling period a progressive total of the values added into the storage locations during a preceding predetermined number of sampling periods;

means for deriving an indication that a predetermined fraction of the total has been at least equalled and means for registering an address representing the frequency range included in location currently being scanned at the time when the indication occurs.

2. Apparatus as claimed in claim 1 in which the means for identifying frequency components includes means for detecting peaks in said formant waveform and for producing peak representing signals;

and means for evaluating time intervals elapsing between successive peak representing signals.

3. Apparatus as claimed in claim 2 in which the peak detecting means includes full-wave rectifying means for rectifying the speech signal.

4. Apparatus as claimed in claim 3 in which the frequency component identifying means includes means for generating a train of pulses spaced at constant time intervals;

a second store holding in addressable storage locations a sequence of values representing limits of the frequency ranges in order of decreasing frequency, the values being expressed in terms of said time intervals;

control means responsive to a first peak representing signal from the peak detecting means to select from the second store the first value of the sequence;

means for accumulating pulses from the train to form a total; and

means for comparing the accumulated total with the value selected from the second store, the control means also being responsive to the comparing means to select from the second store a new value in the sequence whenever the accumulated total equals the value currently selected from the second store and responsive to the occurrence of a second peak representing signal to register the address of that second store location containing the value currently selected, to signify the frequency range of a waveform component.

5. Apparatus as claimed in claim 4, in which the control means is responsive to a predetermined accumulated total occurring before the second peak representing signal to inhibit the registration of the second store address.

6. Apparatus as claimed in claim 1 wherein the first store has a plurality of segments each containing said plurality of locations associated respectively with said range of frequencies and having control means including means for selecting the segments in cyclic rotation during this histogram evaluation period, each segment being selected to enable its locations to accept the addition of unity values during a whole sampling period;

means for addressing during the sampling period the locations of the unselected segments in two successive scanning cycles, the addressing means in each cycle selecting corresponding locations of the segments taken in turn, all the locations being selected in order of their associated frequency ranges.

7. Apparatus as claimed in claim 6 further including means operable during the scanning cycles to accumulate the values in the locations to produce a progressive total of the values;

means operable during the first scanning cycle to register a predetermined fraction of the total of the stored values in the unselected segments; and

second comparing means operable during the second scanning cycle to compare the registered fraction with the progressive total as it is accumulated.

8. Apparatus as claimed in claim 1 including means for extracting a formant waveform from each speech signals respectively on each of a plurality of channels, and further including means associated with each channel for registering the occurrence of a peak in that channel;

means for repeatedly interrogating the peak registering means for the channels in predetermined order to generate peak-representing signals for those channels in which a peak has occured within a predetermined time interval and for applying the peak representing signals to the frequency component identifying means; and

address selection means for controlling the sequential selection of the first store location addresses to select only those locations associated with a single channel during a single histogram evaluation period.

9. Apparatus as claimed in claim 1 having means for extracting more than one formant waveform from the applied speech signal in which the first store has a plurality of separate sections, each section having said plurality of storage locations and being connected to receive values relating respectively to a different formant waveform;

in which the first store has location addressing means connected in common to all the sections.