At present there are no adequate means for objective quality assessment of low bit-rate audio codecs. Subjective assessments or listening tests will play an important role in the evaluation of these codecs for at least a few more years. Three large tests for ISO MPEG/Audio and the very extensive tests performed by CCIR TG 10/2 were all performed with a methodology-Triple Stimulus Hidden Reference-originally developed and proposed by the Swedish Broadcasting Corporation. This paper describes the method and discusses different factors that have to be taken into account when a subjective assessment is to be performed. Results from different tests are compared.
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