Hi @Sparky, With the QA40x software running, you can point your browser to: localhost://9402 and the API should come up.
More info is at the link below. The stuff at the link below uses curl to “drive” things, which is a pretty good place to start. it also shows how to get started with C# or Python. If you look at the Tractor source you mention, you’ll see a more refined example in C#.
User @blurpy also wrote an impressive browser-based means of controlling the QA40x located HERE. In the source file analyze.js you can see where the various primitives are converted into js rest calls.
So, hopefully there’s enough there to get started in C#, Python, JS or raw http via curl. But holler if anything is confusing.
PS. There’s also a way to send/receive the samples directly from the hardware over USB. This leaves a lot of heavy lifting up to you for things like computing THD (REST makes those types of measurements easy). But if you think you’ll get boxed in by the REST API for what you want to do, the bare_metal route might be an option to consider too. See more HERE. And HERE. Inside the first post you’ll see some posts from @IDC_Dragon who wrote a music player in Python using the bare_metal interface. I still marvel at the brevity of Python for doing low-level USB communications. His code there is easy reading too.