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A new distortion measurement

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This article describes a new technique for measuring non-linearity distortion which gives much better correlation with subjective assessment of sound quality than does the conventional total harmonic distortion measurement. Known as the double comb-filter method, it uses pseudo-random binary test signals and largely digital processing, so the cost of instrumenting it can be expected to fall with the increasing availability of l. s. i. circuits. Ultimately, the hardware may cost less than that used at present for t. h. d. measurement. Ways are suggested for using the new technique to measure cross-over distortion, transient intermodulation distortion and other parameters such as ″wow″ and ″flutter″ and linear distortions. The BBC is now testing it on sound-signal transmission circuits and studio equipment.
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... predictability and repeatability). Belcher [4] input maximum length sequences (MLS) rich in harmonics to the DUT and processed the output through comb filters, revealing distortion components attributable to the DUT. This test is claimed to yield results which correlate more closely to listener preferences than do normal sine wave tests. ...
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