Simon brown!
A long time ago I owned a perseus and discovered changing the visual gain would also effect the DSP.
We fixed that bug.
Now, in an effort to reduce noise, I bought a mac mini 7,1 and put windows and SDR-Console on it.
I set it up as "server" with my airspy discovery attached.
See attached picture. This is what happens whenever I set the visual gain to anything below 10db, at or above 9mhz visible.
Below 7mhz it behaves a little differently but there is still problems, particularily if I set the gain to anywhere under zero.
With the LNA on, the bug doesn't appear.