Notepad-12FX : Does a good job recording synths over USB.

Excellent sound. It seems just right for my setup: currently a Volca Bass, Microfreak and Medusa plugged into mono channels, and Blofeld and Model:Samples in two stereo channels. It has one mono channel and one stereo (but RCA version) still available. I use the secondary headphone output as send effect (Ocean Machine effect pedal) which returns a stereo signal.

I just wish the onboard effects could be effective even when receiving an effect return. Also it would have been nice if all channels would be recorded separately over USB (it can do two mono channels, or the stereo mix).

Also, for a beginner without experience in mixing, I found it a bit obscure to fiddle with synth volume, input gain and the proper channel levels for my effect send pedal, which can crackle if the input is too loud. Most of the time I can resolve any issue quickly, though.

I suspect isolated brief drop-outs in the recorded audio were produced in my laptop (i7, 16 GB, Windows 10, Audacity) by background processes.