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Limitations of a synthetic tests (THD, IMD etc.)
post Jan 13 2013, 21:50
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THD is measured on one single frequency (tone) at once, IMD with two tones.
So these measurements are made with synthetic signals while music and speech aren’t just pure tones but rather complex sounds.

For example IMD is calculated on two tones 19 kHz and 20 kHz like here. http://nwavguy.blogspot.com.ar/2012/04/odac-released.html
Just one example of possible many. IMD between 20 kHz and 19 kHz tones ends with 1 kHz tone (20-19 kHz) in audible band. But at the same time there can be 20.1, 20.11 … and 19.1, 19.11… kHz tones those will also cause the same 1 kHz tone in audible band. A classic IMD measurement is calculated only for one pair of tones and not for all other. Wouldn’t be it a huge oversimplification? I’m afraid a testing of audio equipment will be very hard on a real life signals (music, speech).

This post has been edited by IgorC: Jan 13 2013, 21:55
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post Jan 14 2013, 07:08
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Unfortunately the "standards" are far too loose and allow for inferior equipment makers to make dubious claims. For example I feel that amplifier makers should be forced to run full 20-20k white noise before publishing power handling/thd levels rather than "100 watts x 6......" (but only if you run one channel at once at 1khz)
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