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Comment by i_am_proteus | Hacker News Reader

Especially because measurements like Total Harmonic Distortion (THD) use sine waves for their measurements. People pay thousands of dollars for marginally lower THD (say, .02 % instead of 0.5%) but they listen to music, not sine waves.

Well, I assume this. Perhaps people buy high end audio equipment so they can listen to sine waves.

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THD is a measure of non-linearity, which adds harmonics not present in the original signal. Yes, the standard tests use sine waves, but the results are applicable to other signals. Just because most people don't listen to sine waves for fun doesn't mean it's a valid measurement.

On the other hand, the highest THD in a sound reproduction system comes from the physical transducers. Worrying about the THD of an amplifier makes little sense when the speakers provide an order of magnitude more distortion.

-I fully agree with your sentiment, except I'd like to stress that a loudspeaker provides _several_ orders of magnitude more distortion than a competently designed amplifier driven within its limits.

This is the reason for measurements of intermodulation distortion and THD+N by frequency. A proper evaluation of, say, a power amplifier will look at a dozen, maybe a couple dozen different measurements; taken all together, these provide a reasonably complete picture of how the amp performs.

But - from an engineering perspective, music can in fact be decomposed into a series of sine waves - and effectively all digitally recorded music goes through this process as part of a/d conversion (sort of; it's complicated) or FFT-based digital equalization. See: https://en.wikipedia.org/wiki/Fourier_analysis

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