Are you talking about the flute-like sound? If so, you are right to start with a pulse, but you might also consider it’s less abrasive cousin, the triangle wave (harmonics decrease exponentially versus linearly for square/pulse). Add some filtering, with some noise as plosives for the flute, and then some delay and reverb… This video https://www.youtube.com/watch?v=5FDOD7HL6RI goes through flute sound creating with a hard synth and should be helpful.