Sometimes I do use my rig in SSB mode, not for QSO but for experiments. A wave file containing a sweep signal is played on a PC, and the audio signal is fed into IC-7410 via USB I/F. The RF output into a dummy load is monitored with SoftLC44 and HDSDR.
Instead of a sweep signal, you can use, say, a 1kHz pure tone, to fine-tune HDSDR so that you will have a beat frequency of almost 0Hz between the original and the received signals. IC-7410’s TX frequency is set to 7.050.000Hz, so you can see from the figure that there is a 11Hz difference between the two nominal frequencies.
Since you now have the perfect tuning point, you can hear the effect of tuning errors of a few Hz by playing the audio file containing human voices, and by intentionally giving some offset to the tuning. Can you tell the difference when there is a tuning error of just 1Hz?