Bad Snacks walks through adding a lead melody to a loop in Ableton Live using Operator, the built-in FM synthesizer. After muting the chord track to reduce clutter, she browses Operator's lead presets and lands on "basic sine drive" as a clean, focused starting point.
The melody is recorded live from a computer keyboard, keeping notes strictly within the key of C and building a short repeated riff. After recording, a quick quantize with Command+U locks everything into a tight, in-time result.