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Abstract

A device, for digitally measuring in real-time analog telephony signals appearing on a subscriber line during a telephone call thereover, having a converter for converting analog subscriber line voltages into corresponding digital samples, a memory for storing a number of these samples and a processor which resides in any one of various states. For each such state, the processor generates at least one different mask condition, the condition being a limit value of a pre-defined characteristic of at least a particular one of the stored digital samples relative to other such samples. The processor occupies various states with the selection of any one of these states depending upon a particular previous and/or subsequent history of the line voltages with respect to that call, i.e. the state of the call. The processor checks whether some of the stored digital samples satisfies the mask condition. If the condition is satisfied, the device has recognized the digital samples as being a particular converted analog voltage. Only a small number of stored digital samples is required for a test with a mask condition and only a small number of mask condition is needed to identify each such signal, thus permitting one device to provide real-time measurements for a relatively large number of different subscriber lines.

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