Abstract: A digital dual tone multi-frequency (DTMF) tone receiver having a detector circuit for scanning incoming audio signals for possible presence of DTMF tones, and a verifier circuit for verifying the presence of the detected DTMF tones. The detector circuit performs successive discrete Fourier transforms on the incoming signal at a first level of accuracy, and in response generates a tone verify flag signal for indicating whether or not a DTMF tone has been detected. The verifier circuit is enabled in the event that the tone verify flag signal indicates detection of a DTMF tone. The verifier circuit then performs further discrete Fourier transforms on the incoming signal at the detected DTMF frequencies as well as frequencies adjacent thereto, at a second level of accuracy greater than that provided by the detection circuit. The verifier circuit generates a tone present flag signal for indicating whether or not the detected DTMF tone is actually present.

Abstract: A digital signal processing system for use as a digital service unit within a communication switching system, comprised of a plurality of digital signal processing (DSP) modules for connection via a dedicated programmable digital switch forming part of a circuit switch matrix, to one or more input/output ports such as line circuits, trunk circuits, etc., under control of a main system controller, such as a microprocessor. Applications programs for implementing predetermined service features, are downloaded from the main controller via the circuit switch matrix and digital switch, to one or more of the digital signal processing modules for storage within internal memories thereof. The main controller dynamically allocates circuit switch and message channels of the programmable digital switch in accordance with the signal bandwidth and computation power required to implement the predetermined service features.