engleski

Audio Quality Measurements in Communication Systems

ITU gives P-class recommendations for the measurement of audio quality in communication systems. The recommendations are based on system transfer function estimation, nonlinear distortion measurement and perceptual evaluation of audio signal degradation. This work shows and discusses implementation of these methods in real-time "point-to-point" testing of communication systems. A refinement of existing Fourier analyzer technique, a multitone distortion testing, and modulation quality evaluation in speech testing are presented. Modern digital communications introduce new types of signal degradation: coding distortions, time varying delays, time variance of system parameters (gain and noise floor) and even a time clipping in VoIP systems. Echo canceling systems impose restriction on selection of excitation signals in distortion testing, as well as on selection on minimal length of signal analysis window. After analysis of these factors, the work suggests use of excitation signals that are slightly different from those proposed in ITU_T recommendations. The work also presents new perceptual method for the evaluation of speech quality called MQE. It is based on speech modulation quality evaluation and can be used in real time.

audio quality; communication system

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