Hello,
During evaluation I detected an "undocumented feature" (bug) on ToneGenerator. At frequencies below 10 Hz (8ksps) the level drops drastic. It looks like a cutoff. Attached file contains a "very low frequency generator block". I tested it down to 0.1 Hz and still kept level stabil. Just the 20bit computation uncertainties makes the signal jitter.
I used it to simulate fade and other effects in my design. Maybe it is useful for you, too.
Regards
Guenther