This paper presents the results of measurements of speech intelligibility in the digital telecommunication channels with delta modulation coding. Our research included comparative subjective measurements carried out with a traditional intelligibility test and objective measurements utilizing automatic speech recognition procedures. The experiments were performed for various codecs and channel capacities and with white additive noise introduced in the digital channel between the coder and decoder. The results indicated that for a reliable evaluation of speech transmission quality, the type of codec, its mode of operation and transmission conditions should be known.
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