US 4,542,525 A · Method and apparatus for classifying audio signals

Abstract

The null transitions of an audio frequency signal are converted by Schmitt trigger circuits, one of which has a small hysteresis range centered on the null value and the other of which has a much larger hysteresis range likewise centered on the null value, into two binary pulse sequences of variable pulse lengths. The Schmitt trigger circuits are so constituted that a positive pulse length is produced by a negative null transition of the audio signal and vice versa and, moreover, the Schmitt trigger circuits return to their quiescent state 2 milliseconds after a positive null transition of the signal, also producing a positive pulse length, in this case beginning the indication of the pause. The pauses in the two binary pulse sequences thus produced, which exceed predetermined length (60 milliseconds in both cases and, additionally, 30 milliseconds in the case of the pulses formed by the Schmitt trigger with the narrower hysteresis range) and from the three different pause detection operations logic circuits derive either a speech recognition signal, a music recognition signal or an indication of an unidentifiable signal. The logic circuit uses as criteria the number of pauses and the time span of simultaneous or alternating appearance of signal pauses derived from the two different pulse sequences.

Claims28

Dependent claims

Method of automatic classification of audio signals based on conversion of the null transitions of an analog audio frequency signal into at least one pulse sequence by reference to voltage thresholds determined by an absolute value of voltage difference from the null value of the analog signal, comprising the steps of:

converting said analog audio frequency signal into a first binary pulse sequence by use of first voltage thresholds determined by a first absolute value of voltage;
converting said analog audio frequency signal into a second binary pulse sequence by use of second voltage thresholds determined by a second absolute value of voltage substantially higher than said first absolute value of voltage;
detecting the pauses of said first binary pulse sequence which exceed a predetermined first time lapse magnitude and thereby producing a first derived pulse sequence;
detecting the pauses of said first binary pulse sequence which exceed a predetermined second time lapse magnitude which is substantially greater than said first time lapse magnitude and thereby producing a second derived pulse sequence;
detecting the pauses of said second binary pulse sequence which exceed a predetermined third time lapse magnitude which is at least about the same magnitude as said second time lapse magnitude and thereby producing a third derived pulse sequence;
determined whether said audio-frequency signal is a speech signal, a music signal or an unidentifiable kind of signal from said derived pulse sequences, by pause count and by simultaneity and/or alternation of pauses detected by said pulse sequences respectively derived from said first and second binary pulse sequences, and
preparing readiness for repetition of said method when said determining step is completed. PG,21

4 more elements

Apparatus for connection to a source for automatic classification of audio-frequency signals received from a transmission or recording channel for classification of said signals as speech, music or unidentified signals, comprising:

first and second Schmitt trigger circuits having their inputs connected to said source of audio-frequency signals and having their hysteresis thresholds substantially symmetrically disposed about the null potential of said audio frequency signals as supplied by said source, both said Schmitt trigger circuits having two possible states, one of which corresponds to an initial state in absence of said audio-frequency signals and being equipped with means for assuring return of said circuits to said initial state after an interval of at least one millesecond in the other of said states, said first Schmitt trigger circuit having a small hysteresis voltage range and said second Schmitt trigger circuit having a substantially larger hysteresis voltage range than said first Schmitt trigger circuit;
first and second monoflop timing circuits connected to the output of said first Schmitt trigger circuit for respectively detecting pauses in said audio-frequency signal exceeding first and second predetermined time lapse values;
a third monoflop timing circuit connected to the output of said second Schmitt trigger circuit for detecting gaps in higher amplitude portions of said audio signals exceeding a third predetermined time lapse value, and
an evaluation circuit connected to the output of said first, second and third monoflops and containing counters for counting said pauses and gaps detected by said respective monoflop timing circuits, and fourth, fifth and sixth timing circuits, said counters and said fourth, fifth and sixth timing circuits being interconnected for providing signal classification output signals, said evaluation circuit including means for resetting at least said counters promptly after signal classification output signal has been produced.

1 more element

Dependencies are inferred from the claim text.

Method and apparatus for classifying audio signals

Life of this patent

Method and apparatus for classifying audio signals

Life of this patent

Abstract

Claims28