The MX663 decodes the standard audible tone signals provided by telecom systems worldwide to indicate Dial, Ringing, Busy, Unobtainable and other stages of a call attempt. It provides the key features needed for intelligent, full-function, call progress monitoring by applications involving machine dialing or automatic call placement. The MX663 also incorporates the following features: Single and dual tone decoding for better cross-system Call Progress monitoring. "US Busy" tone detector, saving time needed for "cadence verification" under Busy and Unobtainable conditions. This incorporates a separate 620Hz detector for improved response. A detector to indicate speech and non-call progress signals; this reduces voice falsing of call progress tones and adds Voice-Answer detection as a "connected" prompt. A fax and modem tone decoder. A separate, adjustable threshold, signal-level detector which reduces noise falsing. The MX663 uses digital signal processing techniques to provide these advantages. It is a low cost, low power product with superior performance. The MX663 may be used with a 3.0 to 5.5 volt supply and is available in the following packages: 16-pin SOIC (MX663DW) or 16-pin PDIP (MX663P).