Analog voice activity detector for telephone
Voice activity is detected by comparing an analog signal with two voltage thresholds and producing data representing the energy of the signal. The data, in binary form, is compared with thresholds to determine voice activity. In accordance with another aspect of the invention, the thresholds are adjusted based upon statistical information. In accordance with another aspect of the invention, the data can be weighted to provide an indication of the quasi-RMS energy of an input signal. The input signal itself is not converted into digital form yet the data derived from the input signal has high resolution.
1. A method for analyzing the energy content of an electrical signal for detecting voice, said method comprising the steps of:
(a) defining a first voltage threshold and a second voltage threshold, wherein the first threshold is greater than the second threshold;
(b) comparing the signal with the first voltage threshold and the second voltage threshold to produce a digital number representative of the signal;
(c) repeating steps (a) and (b) to produce a plurality of numbers;
(d) converting the plurality of numbers into a first sum; and
(e) comparing the first sum to a third threshold, wherein a sum exceeding the third threshold is indicative of a voice signal.
2. The method as set forth in claim 1 wherein said converting step includes the steps of:
weighting each number representative of a signal; and
summing the weighted numbers.
3. The method as set forth in claim 2 wherein larger numbers receive greater weight than smaller numbers to produce a quasi-RMS calculation.
4. The method as set forth in claim 1 and further including the steps of:
counting the number of numbers that exceed the first threshold;
comparing the number to a fourth threshold; and
indicating a voice signal when the first sum exceeds the third threshold and the number exceeds the fourth threshold.
5. The method as set forth in claim 1 and further including the steps of:
counting the number of numbers that exceed the first threshold;
comparing the number to a fourth threshold; and
increasing the first threshold when the number is greater than the fourth threshold.
6. The method as set forth in claim 1 and further including the steps of:
counting the number of numbers that are less than the second threshold;
comparing the number to a fourth threshold; and
decreasing the second threshold when the number is less than the fourth threshold.
7. The method as set forth in claim 6 and further including the step of:
not counting the number of numbers that are less than the second threshold while the first sum exceeds the third threshold.
8. A method for analyzing the energy content of an analog electrical signal, said method comprising the steps of:
(a) defining a first voltage threshold and a second voltage threshold, wherein the first threshold is greater than the second threshold;
(b) comparing the analog electrical signal with the first voltage threshold and the second voltage threshold to produce a digital number representative of the signal;
(c) repeating steps (a) and (b) to produce a plurality of numbers;
(d) converting the plurality of numbers into a sum.
9. The method as set forth in claim 8 wherein said converting step includes the steps of:
weighting each number representative of a signal; and
summing the weighted numbers.
10. The method as set forth in claim 9 wherein larger numbers receive greater weight than smaller numbers to produce a quasi-RMS calculation.