Thomas, et al,
"Spectroid" by Carl Reinke, or any audio spectrum display available for a smart-phone or tablet, works. While I applaud HF Signals for making a utility available for the purpose, it's chiefly just a graphic display of the audible sound range.?
You'll have to self-impose the 300 - 3,000 hz SSB window on the display, doing your best to set the BFO to fill that range more or less equally.? Me? I like to put just a little higher than lower by a thin margin so as to drop my voice lows and favor the highs,? for punch though the QRN.?
Ted
K3RTA
Ted