Both side of Harmonica, one side is key C, the other side is Key G Color for choose: silver OR golden. The tremolo harmonica‘s distinguishing feature is that it has two reeds per note, with one slightly sharp and the other slightly flat.This provides a unique wavering or warbling sound created by the two reeds being slightly out of tune with each other and the difference in their subsequent waveforms interacting with each other. These so called 2-voice instruments are ideally suitable for traditional folk music.