Tremolo harmonicas are Diatonic models constructed with double holes, each containing two reeds tuned to the same note, one tuned slightly higher than the other. Since both reeds are either blow or draw, when played both will sound together - the slight difference in tuning creating a beautiful vibrating or tremolo effect. Tremolo models are popular for ballads and gospel music, as well as for Latin, Asian, European and other international folk styles. Each individual instrument has 24 double holes and 48 reeds.