of the string is required the strings are designated 1 to 6 (from the 1st the high E to the 6th the low E) with figures 1 to 6 inside circles. The positions (that is where on the fretboard the first finger of the left hand is placed) are also not systematically indicated, but when they are (mostly in the case of the execution of barrés) these are indicated with Roman numerals from the position I (index finger of the left hand placed on the 1st fret: F–B–E–A–C–F) to the position XII (the index finger of the left hand placed on the 12th fret: E–A–D–G–B–E; the 12th fret is placed where the body begins) or higher up to position XIX (the classical guitar most often having 19 frets, with the 19th fret being most often split and not being usable to fret the 3rd and 4th strings). Alternation To achieve tremolo effects and rapid, fluent scale passages, and varied arpeggios the player must practice alternation, that is, never plucking a string with the same finger twice. Common alternation patterns include: i–m–i–m: Basic melody line on the treble strings. Has the appearance of "walking along the strings". a–m–i–a–m–i: Tremolo pattern with a triplet feel (i.e. the same note is repeated three times) p–a–m–i–p–a–m–i: Another tremolo pattern. p–i–p–i or p–m–p–m: A way of playing a melody line on the lower strings. Tone production Classical guitarists have a large degree of freedom within the mechanics of playing the instrument. Often these decisions influence tone and timbre. Factors include: At what position along the string the finger plucks the string (This is changed by guitarists throughout a song, since it is an effective way of changing the sound (timbre) from "soft" (dolce) plucking the string near its middle, to "hard" (ponticelo) plucking the string near its end). Use of the nail or not: Modern classical guitar playing uses a technique in which both the nail and the fingertip contact the string during normal playing. (Andrés Segovia is often credited with popularizing this technique.) Playing with either fingertips alone (dita punta) or fingernails alone (dita unghis) are considered special techniques for timbral variation. Concert guitarists must keep their fingernails smoothly filed and carefully shaped to employ this technique, which produces a better-controlled sound than either nails or fingertips alone. Playing parameters include: Which finger to use What angle of attack to hold the wrist and