A waveform read off a landscape. Define a 3-D surface z = f(x, y), send an orbit looping across it once per period, and read the height under the path — that height over time is the sound. Because the path is two-dimensional, a small change to the orbit (its radii, its Lissajous ratio) drags it across entirely different hills and valleys, so the timbre shifts in ways a 1-D wavetable never could. Try a circular orbit on the saddle — height = x·y = a pure octave up — then stretch the orbit and watch harmonics bloom.
play a note (a s d f …) and sweep the orbit radii and ratio to reshape the tone