The methods for assessment of speech quality fall into two classes: subjective and objective methods. This paper includes an overview of selected methods of subjective listening measurements (ACR, DCR) recommended by ITU-T. The influence of a bit-rate value on the sound quality was a subject of research presented in this paper. The influence of the Spectral Band Replication (SBR) process on the speech quality was also investigated. The tested samples were taken from the Digital Audio Broadcasting experimental emission in Poland as well as from an internet network. The subjective assessment for DAB speech signals has been performed with the use of both: ACR and DCR methods. It turned out that SBR process influences significantly the speech quality at the lower bit-rates making it as good as for higher bit-rates. It was also found that for higher bit-rate values (96 kbit/s, or higher), the use of both methods causes the different results.
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