Tomahawk, you can experiment with different diameter air channels. These 2 calls have a 1/4" air channel that steps up to 1/2". A 3/16" air channel will produce a nice high pitch sound, but you have to deepen the air channel through the toneboard to allow enough air flow. The reeds are 0.010" mylar.
CWJ, these are open reed calls. The only thing that covers the reeds is your mouth. They are a bite style call. Depending on where you apply pressure to the reed, determines the pitch and tone of the call.
Brian.