Measurement of signal quality

Abstract

A test stimulus includes two signals R , S. Signal S is transmitted to a customer equipment interface and over a system under test to a complementary remote apparatus. The test apparatus has two inputs processed by a number of functional elements. The first input is the reference signal R . The other input is a corresponding test signal R′ generated at remote test apparatus as a test signal R, identical with reference signal R , and transmitted over the system under test via the customer interface. These two versions of the same test signal are compared. Firstly, the signals R , R′ are processed by a psycho-acoustic model, the output of which is transmitted to a perceptual layer, and then to a conversion unit which also receives a further input from a non-optimum loudness rating unit. The output from the conversion unit is transmitted to a signal quality determination unit, which also receives an input from the customer equipment interface. The non-optimum loudness rating unit processes inputs from the customer equipment interface and signal generator. During an iterative process, the signal generator receives feedback control from the signal quality determination unit. The remote test apparatus similarly receives a modified version of signal S (viz S′) from the network and compares it with a locally-generated reference version S . In an alternative arrangement the same test apparatus is connected to both test points of the network and processes both signals S and R, either serially or in parallel.