Signal analyzing system

An analog communication signal such as the signal transmitted over a telephone line is converted to digital form for storage in the memory of a computer. Segments of the digital representation of the signal are analyzed to determine whether or not the signal has uniform frequency components repeating at regular intervals. Detection of such regularly repeating uniform frequency components is useful in an automated telephone system to determine whether a telephone signal consists of voice or a call progress signal.

We claim:

1. Mechanism for analyzing an analog signal represented by digital samples to determine whether the signal has uniform frequency components repeating at a selected period comprising means for selecting a first set of the digital samples representing a first segment of the signal beginning at a predetermined point in time, means for selecting a second set of the digital samples representing a second segment of the signal which second segment begins later than the first segment by an interval equal to the selected period, each sample of the second set corresponding to one sample of the first set taken earlier than such sample of the second set by an interval equal to the selected period, and means for detecting whether there is correspondence between the samples of the first set and the samples of the second set, respectively, indicative of a signal having the uniform frequency components.

2. The mechanism defined in claim 1, in which the detecting means includes means for comparing the values of samples of the second set to the values of samples of the first set.

3. The mechanism defined in claim 1, in which the detecting means includes means for calculating the product obtained by multiplying the value of each sample of the second set by the value of the corresponding sample of the first set.

4. The mechanism defined in claim 3, in which the detecting means includes means for adding all of the products to obtain the product sum.

5. The mechanism defined in claim 4, in which the samples have integral values ranging from a negative integer to a positive integer, the detecting means including means for adding the absolute values of each of the samples of the first set and the samples of the second set to obtain the absolute value sum.

6. The mechanism defined in claim 5, in which the detecting means includes means for comparing the product sum to the absolute value sum.

7. Mechanism for analyzing an analog signal represented by digital samples to determine whether the signal has components of uniform frequency comprising means for selecting a first set of the digital samples representing a first segment of the signal beginning at a predetermined point in time, means for selecting several other second sets of the digital samples each of which second sets represents a segment of the signal beginning later than the first segment by a delay interval different from the delay interval of any of the other second sets, each sample of each of the second sets corresponding to one sample of the first set taken earlier by the delay interval of such second set, and means for characterizing the degree of correspondence between the samples of the first set and the samples of each of the other second sets, respectively, indicative of a signal having uniform frequency components.

8. The mechanism defined in claim 7, in which the digital samples representing the analog signal are spaced by a uniform sampling period, and the number of samples in the first set is much smaller than the total number of digital samples representing the first signal segment.

9. The mechanism defined in claim 8, the digital samples of the first set being spaced uniformly.

10. The mechanism defined in claim 7, the digital samples being multibit samples each having a sign bit, and the characterizing means including means for detecting whether sign bits of corresponding samples are the same.

11. The mechanism defined in claim 10, in which the detecting means includes means for calculating the exclusive OR value of each pair of corresponding samples having a nonzero value.

12. Mechanism for analyzing signals on a telephone line to detect the presence of call progress signals comprising means for converting the signal on the telephone line to digital samples representing the signal, and means for analyzing the digital samples so as to detect presence of a signal of uniform frequency content over a substantial period indicative of a call progress signal.

13. The mechanism defined in claim 12, in which the analyzing means includes means for selecting a first set of the digital samples representing a first segment of the signal beginning at a predetermined point in time, means for selecting a second set of the digital samples representing a second segment of the signal which second segment begins later than the first segment by a preselected delay interval, each sample of the second set corresponding to one sample of the first set taken earlier than such sample of the second set by said preselected delay interval, and means for detecting whether there is correspondence between the samples of the first set and the samples of the second set, respectively, indicative of a call progress signal.

14. The mechanism defined in claim 13, in which the delay interval is about 0.1 second.

15. The mechanism defined in claim 13, in which the analyzing means includes means for selecting several other second sets of the digital samples each representing a segment of the signal beginning later than the first segment by a delay interval different from the delay interval of any of the other second sets, each sample of each of the second sets corresponding to one sample of the first set taken earlier by the delay interval of such second set, and means for characterizing the degree of correspondence between the samples of the first set and the samples of each of the other second sets, respectively, indicative of a call progress signal.

16. The mechanism defined in claim 15, in which the digital samples have sign bits, the characterizing means including means for comparing the sign bits of corresponding samples.

17. The method of determining whether an analog signal has uniform frequency components which comprises converting the analog signal to digital form, selecting a first set of digital samples representing a first segment of the signal beginning at a predetermined point in time, selecting a second set of digital samples representing a second segment of the signal which segment begins later than the first segment by a preselected delay interval, and detecting whether there is correspondence between the samples of the first set and the samples of the second set, respectively, indicative of a signal having uniform frequency components.

18. The method of detecting whether an analog signal has components of uniform frequency which comprises converting the analog signal to digital form, selecting a first set of digital samples representing a first segment of the signal beginning at a predetermined point in time, selecting several other second sets of digital samples each of which second sets represents a segment of the analog signal beginning later than the first segment by a delay interval different from the delay interval of any of the other second sets, and comparing the samples of the first set and the samples of each of the other second sets, respectively, to detect correspondence indicative of a signal having uniform frequency components.

19. The method of analyzing signals on a telephone line to detect the presence of call progress signals which comprises converting the signal on the telephone line to digital samples representing the signal, storing the digital samples in the memory of a computer, selecting a first set of the digital samples representing a first segment of the signal beginning at a predetermined point in time, selecting a second set of the digital samples representing a segment of the signal beginning later than the first segment, and comparing the two sets of samples to detect whether or not the signal has uniform frequency content over a substantial period of time.

20. The method of detecting the presence of call progress signals on a telephone line which comprises converting the signal to digital samples representing the signal, and analyzing the samples so as to detect presence of a signal of uniform frequency content over a substantial period indicative of a call progress signal.

21. The method of eliminating digital call progress signals from a computer memory bank containing digital voice signals which comprises examining the computer memory bank to detect signal segments having uniform frequency content, and deleting such signal segments from the computer memory bank.