Method and apparatus for classifying audio signals

US4542525A · kind A · utility

Assignee

• Blaupunkt-Werke GmbH · DE

Inventor

• Reinhard Hopf · Lychen, DE

Key dates

• Filing date: Sep 27, 1983
• Grant date: Sep 17, 1985
• Expiry date: Sep 27, 2003

Classification

• Technology area (CPC G): Physics
• CPC primary: G10H2210/046
• WIPO field: Computer technology
• WIPO sector: Electrical engineering

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 …