The HD goes with 2 FFT simultaneously already noticeably down in speed - And then four.....I'm curious whether the developers could still optimize something, so that the performance does not completely collapse in such a case.
Here is one example (SDS1000X HD).
3.665MHz carrier. Modulated with 1kHz and modualtion depth 2% (sidebands -40dBc)
All 4 FFT simultaneously with same settings. Input only to CH1 (F1)
4 FFT's all have 2Mpts (Δf 3.97Hz) And as can see "RBW" is 14.82 (flattop window in use) (time domain t/div is 50ms/div)
(note that time domain decimated samplerate is 50MSa/s and FFT samplerate 8.33MSa/s (1:6)
Yes, processing takes time...just for example, this FFT window update period is 6.8s but time domanin acquisition / trigger in this case around 1s.
Slow for one is fast for some other. Also there is not free lounges.
But then, lets keep some just for fun..
Now there is full span 0- 4.167MHz. I will try with SA... there is not available just same RBW but with 30Hz RBW 127s and with 10Hz RBW 394s.
So what is slow and what is fast..
But naturally if set SA (SSA3021X) for 10kHz span and 10Hz RBW it is faster. Around 1s. Naturally due to its working principle. (in this case its FFT "sweep" handle 4pcs 3kHz slices, 262.348ms each one))