The kaval is a rim-blown flute found, in a variety of forms, throughout the Balkan states as well as in Turkey, Azerbaijan, Armenia, and Kurdistan.

The Bulgarian kaval is made in three sections. The middle section contains seven finger holes and one thumb hole. The bottom section has four always-open holes for venting and tuning.  The most common size Bulgarian kaval has lowest note d’ (approx. 635mm long, and 16mm inner diameter).

Raising the fingers one-by-one produces first a whole tone and then a scale of semitones.  If one starts with the lowest note, opening the seven finger holes one-by-one takes the pitch from d’ to b’b, and then uncovering the thumb hole gives b’. The thumb hole is not used for any other note.  The notes c” and c”# are missing from the range. The second octave starts with d”. Then a scale of a whole tone followed by semitones is obtained.  The notes c”’ and c”’#, and higher notes, are available as third harmonics.

Wikipedia