Correlation of Audio Distortion Specifications
The sensitivity of five audio distortion measurement methods has been investigated with experimental measurements of circuits simulating basic archetypal distortion mechanisms. The results show that the ordinary measurement methods, THD, and SMPTE-IM, do not reveal dynamic distortions, and that every method has unacceptably low sensitivity for at least one distortion mechanism. The combined use of the DIM method and the CCIF-IM method for a complete specification of amplifier distortion is recommended, because their "blind" spots do not overlap. Distortion measurements of eleven commercial power amplifiers and eleven operational amplifiers show a mixture of the archetypal distortion mechanism, mostly dynamic distortions for the operational amplifiers, and mixed static and dynamic distortions for the power amplifiers. The results obtained with the different methods have been found to correlate qualitatively but not quantitatively for each type of nonlinearity separately. In a mixed case and for commercial amplifiers the qualitative correlation disappears, and there seems to be no reliable way of predicting the measurement result of one method from that of another method in the case of an unknown amplifier.
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