Method of and device for testing the quality of digital

Abstract

A device for analyzing the quality of digital speech-transmission equipment, specifically a speech coder, comprises generators of white-noise signals, sinusoidal signals, frequency-shaped signals and artificial speech-like signals connected to the coder and to an adaptive transversal filter in parallel therewith. The filter and the coder feed output signals to a subtractor which produces an error or noise signal by deducting digital samples of the filter output signal from corresponding samples of the coder output signal. The error signal is fed back to the filter during a first testing phase to control the periodic modification of weighting coefficients computed by a multiplicity of updating cells in the filter for multiplicative combination with incoming samples of the test signal. The first phase ends when the coefficients converge to fixed values representative of the linear characteristics of the coder and the error signal assumes a substantially constant near-zero level. In a second testing phase the error signal from the subtractor and the corrected output signal of the filter are fed to a quality analyzer which calculates one or more parameters from a set comprising a total signal-to-noise ratio, a simple segmental signal-to-noise ratio and a frequency-weighted segmental signal-to-noise ratio, the parameters being linearly combined to produce an integer between zero and ten indicative of the transmission quality of the coder.