(due to smaller fluctuations in humidity and temperature of air across the reeds) and the possibility to sing or talk whilst playing make them by far the most popular variation, however mouth-blown smallpipes are fairly common. The chanter is most commonly unkeyed, but occasionally keys are added, most often high B, G sharp, F natural, and C natural, to extend the range and/or give access to accidental notes. A second thumb hole may be added to the back of the chanter to play C natural. Though it would in principle be possible to add as many keys as seen on modern Northumbrian smallpipes, very few sets with more than 3 keys exist. Most music written for the instrument uses only the nine notes of its unkeyed range. The drones, typically three in number, are set in a common stock and are usually tuned in one of two patterns. For pipes in A, the tenor drone is tuned to the low "A" of the chanter (the tonic), and the bass drone to the "A" an octave below this. There is often also a dominant drone - this can be either a baritone, tuned a fifth above the bass, or an alto drone, tuned a fifth above the tenor. For tunes played on the 4th (i.e. in D on an A chanter), the dominant drone can be either shut off or retuned to the fourth on the chanter. Most makers favour a baritone drone, rather than an alto, though some use only the bass and tenor. Some makers have developed drones compatible with both A and D chanters, so that one instrument can be used with either chanter. One example is the "ADAD" style, with bass, baritone, tenor, and alto, as seen here: With longer tuning slides or the addition of tuning beads (used widely on Northumbrian smallpipe drones), drones can easily be retuned to a pitch one or two tones higher. This allows for increased drone tuning options, meaning tunes can be played in the nominal keys of A Mixolydian, D major, B minor and by tuning down by a tone, in G. The use of longer tuning slides is also used to convert A and D drones to G and C drones (or vice versa), meaning the same set of drones can be played with chanters in D, C, A and G. History Originally one of the first documented bagpipes