That calculator, like many others, uses the root-sum-square (RSS) method. That is pretty standard though certain phase relationships can impact the result. Convert each number in dB to a voltage, square it, add it to the other number(s), take the square root of the resultant sum, and then convert back to dB, e.g. 20*log10(sqrt{[10^(-100/20)]^2 + [10^(-80/20)]^2)}) = -79.9567862... dB. Distortion 10 dB or so lower adds less than 1 dB to the result, e.g. -100 dB and -90 dB results in about -89.5 dB net SINAD. Two equal terms degrade the result by about 3 dB, e.g. -100 dB combined with another product also -100 dB results in total SINAD ~ -97 dB.
HTH - Don
The distortions add linearly. Noise doesn't quite.
No, you always get higher noise level. If they have same spectrum and level, then you get 3 dB more noise. The issue is that they may not have the same spectrum or statistical qualities.How is it with noise? Does noise add up at all or is noise level always equal to the level of noisest device in chain?
The distortions add linearly. Noise doesn't quite. So it is not a very simple thing. If you just care about the distortion part, easiest thing is to use the calculator at the bottom of this page: http://www.sengpielaudio.com/calculator-thd.htm
Make sure to use negative values for SINAD:
View attachment 17904
Note that per above example, if the SINAD of one device is much better than the other, its effect is negligible. This is why it pays to use a very transparent amp after a DAC even if the DAC can't rise up to its level. You minimize the additional distortion.
How is it with noise? Does noise add up at all or is noise level always equal to the level of noisest device in chain?
If they have same spectrum and level, then you get 3 dB more noise. The issue is that they may not have the same spectrum or statistical qualities.
I would imagine inherent noise in DACs (random noise all over freq range )to have same spectrum and statistical quaities as in amps, correct?
Btw, what kind of noise is that, is it "pink"? Which parameter in your measurements is noise component of SINAD?
SINAD signal to noise and distortion ratio.
Power of the signal, power of the noise and power of the distortion divided by the power of noise and power of distortion.
It's the obverse of THD+N.
So noise isn't separated out from other components directly.
You could have a component with a very low noise floor and moderate distortion levels so the residual after notching out the test signal is mostly distortion. You could have another component with distortion products pretty much buried in a moderate noise floor and after notching out the signal is mostly noise. Both could even have the same SINAD number, but noise and distortion levels would be rather different.
The idea is if you get SINAD down to very, very low levels, it doesn't matter how you mix or match noise and distortion, all of it is low enough to be inaudible.
As for noise spectrums, they usually are something like pink or between pink or brown assuming they aren't polluted with 60 hz hum, or other garbage.
No, I see fair bit of variation. Many times it has a slope or hump in certain region.I would imagine inherent noise in DACs (random noise all over freq range )to have same spectrum and statistical quaities as in amps, correct?
I know what SINAD is, I was wondering how comes noise is not measured separately as THD is? Is it because THD is dominant component fo SINAD?
No, I see fair bit of variation. Many times it has a slope or hump in certain region.
Okay, I wasn't sure the way you worded it. So my bad interpretation.
I measure it across 22.5 kHz of bandwidth. You can see that in green at the bottom of the dashboard. Using wider bandwidth would naturally lower SINAD (sometimes by a ton).So, in order to get a "true" picture, shouldn't you measure SINAD in the whole audible freq range?
I measure it across 22.5 kHz of bandwidth. You can see that in green at the bottom of the dashboard. Using wider bandwidth would naturally lower SINAD (sometimes by a ton).
The distortions add linearly. Noise doesn't quite. So it is not a very simple thing. If you just care about the distortion part, easiest thing is to use the calculator at the bottom of this page: http://www.sengpielaudio.com/calculator-thd.htm
Make sure to use negative values for SINAD:
View attachment 17904
Note that per above example, if the SINAD of one device is much better than the other, its effect is negligible. This is why it pays to use a very transparent amp after a DAC even if the DAC can't rise up to its level. You minimize the additional distortion.