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THD and SINAD Correlative Math Equation?

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#1
Remind me how THD relates to SINAD again? how do you translate it?

(THD+N ?%)*equation = SINAD ?DB

Thank you
 

DonH56

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#2
SINAD ~ 20*log10(THD+N%/100)
 

March Audio

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#3
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flipflop

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#5
So "distortion attenuation" is sinad?
No, it's the dB equivalent to the THD%. 0.1% = -60 dB.
SINAD is the signal without distortion (and noise). Remove the minus sign and you get SINAD: 60 dB.
 

DonH56

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#7
SINAD = (Signal+THD+N)/(THD+N)

THD+N is not a factor but a term, so it's not signal without distortion and noise.
Depends on what standard you follow... For ADCs and DACs, it is defined as:

Signal to noise and distortion = signal / (noise + distortion)

In this definition the numerator only includes the signal. It is used this way to calculate the effective number of bits, ENOB, and often used in communication systems (digital or analog, at least in the courses and work I have had). Ref IEEE Standards 1241, 1057, O&S, etc. Since my career focused on data converters that is the definition I have (almost) always used. The definition you provided is used more in the RF world and guarantees SINAD can never fall below 1 (so the log never goes negative). My comm theory book defines both but uses the IEEE definition, while my microwave radio book uses "your" definition. Most of the grad classes I took long ago also used the IEEE definition so we got to talk about how our circuits could recover the signal even with "negative" SNR.

Lovely the way we can complicate everything...
 
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