Tremolo harmonicas are a type of harmonica, distinct by having two reeds per note. In a tremolo harmonica the two reeds are tuned slightly off a reference pitch, one slightly sharp and the other slightly flat. This gives a unique wavering or warbling sound created by the two reeds being not exactly in tune with each other and difference in their subsequent waveforms acting against one another. The degree of beating can be varied depending on the desired effect. Instruments where the beating is faster due to the reeds being farther apart from the reference pitch are called "wet", whereas those where the beating is slower and less noticeable due to the reeds being more closely in tune are called "dry".