We can use Max to analyze audio to send the data to TD, or even better, if we generate audio in Max, we can just send the data generating the audio to TouchDesigner. There is no need to do FFT on a stereo sum if we can just get the parameters of a synth directly. Things such as BPM detection or fundamental pitch estimation are possible if we don't have the data directly, but they are, of course, a bit unreliable and unstable.

First, let's look at how Max and Touch can communicate. The weapon of choice here is UDP/OSC. User Datagram Protocol (UDP) is a protocol that is part of the transport layer of the OSI model. Compared to Transport Control Protocol (TCP), it has the advantage of being faster and the disadvantage of being more unreliable, which is not an issue for our purposes most of the time. OSC is, as you probably know, a very widespread protocol, that somewhat became the commonly accepted MIDI successor. We won't go very deep into the structure of OSC, so, for...