Different methods of sound production require different methods of adjustment:
Some instruments produce a sound which contains irregular overtones harmonic series, and are known as inharmonic. This makes their tuning complicated, and usually compromised. The tuning of bells, for instance, is extremely involved.
Tuning may be done aurally by sounding two pitches and adjusting one of them to match or relate to the other. A tuning fork or electronic tuning device may be used as a reference pitch, though in ensemble rehearsals often a piano is used (as its pitch cannot be adjusted for each rehearsal). Symphony orchestras tend to tune to an A provided by the principal oboist.
Interference beats are used to objectively measure the accuracy of tuning. As the two pitches approach a harmonic relationship, the frequency of beating decreases. When tuning a unison or octave it is desired to reduce the beating frequency until it cannot be detected. For other intervals, this is dependent on the tuning system being used.
Harmonics may be used to check the tuning of strings which are not tuned to the unison. For example, lightly touching the highest string of a cello at halfway down its length (at a node) while bowing produces the same pitch as doing the same one third of the way down its second highest string.
In music, the term open string refers to the fundamental note of the unstopped, full string.
The strings of a guitar are normally tuned to fourths (excepting the G and B strings in standard tuning), as are the strings of the bass guitar and double bass. Violin, viola, and cello strings are tuned to fifths. However, non-standard tunings (called scordatura) exist to change the sound of the instrument or create other playing options.
To tune an instrument, usually only one reference pitch is given. This reference is used to tune one string, to which the other strings are tuned in the desired intervals. On a guitar, often the lowest string is tuned to an E. From this, each successive string can be tuned by fingering the fifth fret of an already tuned string and comparing it with the next higher string played open. This works with the exception of the G string, which must be stopped at the fourth fret to sound B against the open B string above.
This table lists open strings on some common string instruments and their standard tunings.
|violin, mandolin||G, D, A, E|
|viola, cello, tenor banjo, mandola, tenor guitar||C, G, D, A|
|double bass, bass guitar*||(B*,) E, A, D, G|
|guitar||E, A, D, G, B, E|
|ukulele||G, C, E, A (the G string is higher than the C and E, and two half steps below the A string, known as reentrant tuning)|
Unconventional tunings, or scordatura (It., from scordare, to mistune), were first used in the 16th century by Italian lutenists. It was primarily used to facilitate difficult passages, but was also used to alter timbral characteristics, reinforce tonalities through the use of open strings, and to extend the range of the instrument.
Violin scordatura was employed in the 17th and 18th centuries by Italian and German composers, namely, Biagio Marini, Antonio Vivaldi, Heinrich Ignaz Biber - who in the Rosary Sonatas prescribes a great variety of scordaturas, including crossing the middle strings - Johann Pachelbel and J.S. Bach, whose Fifth Suite For Unaccompanied Cello calls for the lowering of the A string to G. In Mozart's Sinfonia Concertante in E-flat major (K. 364), all the strings of the solo viola are raised one half-step, ostensibly to give the instrument a brighter tone so as not to be overshadowed by the solo violin. The open D-string then sounds the tonic of the piece, E-flat. However, in modern performance it is often performed without scordatura.
Scordatura for the violin was also used in the 19th and 20th centuries in works by Paganini, Schumann, Saint-Saëns and Bartók. In Saint-Saëns' "Danse Macabre", the high string of the violin is lower half a tone to the E♭ so as to have the most accented note of the main theme sound on an open string. In Bartók's Contrasts, the violin is tuned G♯-D-A-E♭ to facilitate the playing of tritones on open strings.
A musical instrument which has had its pitch deliberately lowered during tuning is colloquially said to be "down-tuned". Common examples include the electric guitar and electric bass in contemporary heavy metal music, whereby one or more strings are often tuned lower than concert pitch. This is not to be confused with electronically changing the fundamental frequency, which is referred to as pitch shifting.
Due to the psychoacoustic interaction of tones and timbres, various tone combinations will sound more or less "natural" when used in combination with various timbres. For example, using harmonic timbres,
More complex musical effects can be created through other relationships.
Many cultures whose dominant instruments emit non-harmonic sounds use other tuning systems, in which other intervals sound more "natural.
The creation of a tuning system is complicated because musicians want to make music with more than just a few differing tones. As the number of tones is increased, conflicts arise in how each tone combines with every other. Finding a successful combination of tunings has been the cause of debate, and has led to the creation of many different tuning systems across the world. Each tuning system has its own characteristics, strengths and weaknesses.
Tuning systems that are not produced with exclusively just intervals are usually referred to as temperaments.
All musical tunings have advantages and disadvantages. Twelve tone equal temperament (12-TET) is the standard and most usual tuning system used in Western music today because it gives the advantage of modulation to any key without dramatically going out of tune, as all keys are equally and slightly out of tune. However, just intonation provides the advantage of being entirely in tune, with at least some, and possibly a great deal, loss of ease in modulation. The composer Terry Riley, said "Western music is fast because it's not in tune", meaning that its inherent beating forces motion. Twelve tone equal temperament also, currently, has an advantage over just intonation in that most musicians are trained in, and have instruments designed to play in equal temperament. Other tuning systems have other advantages and disadvantages and are chosen for various qualities.
The octave (or even other intervals, such as the so-called tritave, or twelfth) can advantageously be divided into a number of equal steps different from twelve. Popular choices for such an equal temperament include 19, 22, 31, 53 and 72 parts to an octave, each of these and the many other choices possible have their own distinct characteristics.
The two paragraphs above assume the use of harmonic timbres, in which the partials' placement follows a pattern of ratios of small whole numbers. Western music uses harmonic timbres almost exclusively, so their use is often assumed in discussions of tuning such as this. However, the timbres of the dominant instruments of some other cultures are non-harmonic, and sound most natural in tunings that do not follow ratios of small whole numbers (except perhaps the octave at 2:1). For instance, William Sethares shows that the tunings of Balinese gamelans are related to the inharmonic spectra or timbre of their metallophones and the harmonic spectra of stringed instruments such as the rebab, just as just intonation and twelve tone equal temperament are related to the spectra or timbre of harmonic instruments alone.
Some instruments, such as the violin, don't limit the musician to particular pitches, allowing to choose the tuning system "on the fly". Many performers on such instruments adjust the notes to be more in tune than the equal temperament system allows, perhaps even without realizing it.
Like the violin and other fretless stringed instruments, the pedal steel guitar places absolute control of pitch into the hands of the player. Most steel guitarists tune their instrument to just intonation. The steel guitar is unique among western instruments in its ability to create complex chords in just intonation in any key. Smooth, beatless chords are part of the steel guitar's characteristic sound.
Likewise, using a tuning invariant isomorphic keyboard to drive a Dynamic Tonality-compatible synthesizer, one can change the tuning "on the fly," adjusting the frequencies of the tuning's tones and of the timbres' partials to sound natural in any tuning across a wide tuning range.