Latency Causes and Cures

[recri]

We can continue the latency discussions here.

One choice to avoid is routing the CW signal through a voice audio input channel with an AGC, compressors, filters, and a phasing SSB modulator.

We can route keyed sidetone, or even keyed IQ, back to the host over usb audio. You can race that against your MIDI keyed samples to diagnose latencies in either channel.

Any CWKeyer firmware could loop back usb audio in directly to usb audio out, loop back MIDI at the usbMIDI interface, and loop back MIDI through the normal operation path. That would characterise the system audio and MIDI latency and the firmware MIDI latency and could be done. With a cooperative operator, you could pick up the clicks from the key on a microphone channel, and put the codec into the audio loopback with a patch from LineOut to LineIn.

So you don't need a scope to diagnose a lot of latency issues, though you'd want one to check the final result.