Knob Roland Boss with white top.
This rotary knob can be found on multiple synthesizers and classic effects pedals from Roland and Boss.

For Roland MKS-50 MKS-60 MKS-70 MKS-80 MPG-80 Micro série MKS MPG

Boss DD2 DD3 DD5 DD6 DD7 RBF10 RCE10 RCL10 RSD10 RDD20 RPD10 RPH10 RPS10 RRV10