I have to think the reason for the notch filter, a time-honored device to extend the dynamic range of a measuring system be it audio, RF, or light, does not apply to a SW implementation? The dynamic range is set by the signal capture (ADC) so what is the benefit of applying a notch filter in SW in this application? Help to find the remaining spurs?
Curious - Don
You may want to have a look at this thread
In my previous measurements, I was peaking around 122dB SINAD measurement, with a direct ADC connection Using E1DA Cosmos APU Notch, (and some lessons learned from last REW editions), I was finally able to achieve a more relevant SINAD measurement of the D90LE Measurement is done with Topping...
In practice, the AES17 notch is usefull with digital measurement when the fundamental, through the DUT, an analog notch filter, or from the signal source, shows some spread around its base frequency.
In my case, that was due to the E1DA APU notch filter. I see that also when I use Victor's 1kHz oscillator.
If I measure my RME ADI-2 Pro in loopback mode, the results are identical with or without the AES17 digital notch.
Not at all with the APU or Victor's oscillator.
The AP also uses analog oscillator and notch for high accuracy measurements and, therefore, also requires the same.
I suspect the AES 17 standard includes this to allow use of such analyzers.
The question is: do they compensate for the narrower bandwidth in noise and THD+N calculations ?
Ok, we speak 0.3dB or so, but I'm curious.
As per the AES-17 standard definition, it doesn't seem so.