Challenge:
How do I use renoise to add a sine to a square wave?
I can get a sine and I can get a square from the element instrument set, and I can draw waves if I want to, but how do I add the sine wave to the square wave to make a combined instrument?
Why would I want to do it?
Because I’m trying for an old school, presampling sound and I want to build my waves from the ground up.
If I can do this in renoise, I can achieve an astonishing array of things without having to spend too much time twiddling VST or external synth parameters.
I understand that I could just trigger two instruments at once and in theory get pretty much the same result, but that’s much messier.
This is one of those things where there’s a million different ways to go about doing it. For starters you could use this tool:
http://renoise.com/tools/custom-wave-synth
This tool is pretty much the easiest way to do it. You can set the amplitude and frequency multiplier independently for each operator, and use either single cycle or set the number of cycles.
Another thing you can do in Renoise is combine stereo channels. If you have 2 samples of equal length you want to combine, like a square and a sine, you can copy paste them into a stereo sample. For example, square on top, sine on bottom. Now click the adjust button, and change stereo to mono, and it will combine the waves into a mono wave.
something like this?
made a simple macro crossfader 
SQUARE-SINE.xrni
Thank you both.
Carbonthief, you win. That tool looks like everything I want in a box. I’ll be making old school Tangerine Dream sounds with it in minutes.