just a 3x oscillator, two of them on sine waves (both at same octave) and one turned off, quick and sharp attack, no hold, little sustain, little decay and almost medium release. add a chorus plugin to it and cut out every frequency except between low mids & mid. add some reverb and you're good to go.
(Play with the sustain a little until it sound like someone playing an instrument)
on Synthwave loop by P3TRUS
on lo fi pop synths by sylvette
(Play with the sustain a little until it sound like someone playing an instrument)