Everything about Semitone totally explained
A
semitone, or
half-step is a
musical interval. It is the smallest interval commonly used in Western music, and is considered the most
dissonant. The most commonly written form of this interval is the
minor second, notated using two adjacent letter names (for example
C and
D♭), but the
augmented unison is also used, both notes having the same letter-name, with one of the notes being inflected by an accidental (for example
C and
C♯).
In
twelve-tone equal temperament all semitones are equal in size. Any equal-tempered interval can be defined in terms of an appropriate number of semitones (for example an
octave is 12 semitones wide). In other tuning systems the term "semitone" refers to a family of intervals which may vary both in size and name. Often a distinction is made between a
diatonic semitone (notated as a
minor second), and a
chromatic semitone (as an
augmented unison). These are
enharmonically equivalent in equal temperament.
Minor second
The
minor second occurs in the
major scale, between the third and fourth degree, (
mi and
fa), and between the seventh and eighth degree (
si and
do). It is also called the
diatonic semitone because it occurs between steps in the
diatonic scale. The minor second is abbreviated
m2. Its inversion is the
major seventh (
M7).
Melodically, this interval is very frequently used, and is of particular importance in
cadences. In the
perfect and
deceptive cadences it appears as a resolution of the
leading-tone to the
tonic. In the
plagal cadence, it appears as the falling of the
subdominant to the
mediant. It also occurs in many forms of the
imperfect cadence, wherever the tonic falls to the leading-tone.
Harmonically, the interval usually occurs as some form of
dissonance or a
nonchord tone that isn't part of the
functional harmony. It may also appear in inversions of a
major seventh chord, and in many
added tone chords.
Frédéric Chopin's
Étude Op. 25, No. 5 opens with a melody accompanied by a line that plays fleeting minor seconds. These are used to humorous and whimsical effect, which contrasts with its more lyrical middle section. This eccentric dissonance has earned the piece its nickname: the "wrong note" étude. This kind of usage of the minor second appears in many other works of the
Romantic period, such as
Modest Mussorgsky's
Ballet of the Unhatched Chicks.
Augmented unison
The
augmented unison doesn't occur between diatonic scale steps, but instead between a scale step and a
chromatic alteration of the same step. It is also called a
chromatic semitone. The augmented unison is abbreviated
aug 1. Its inversion is the
diminished octave (
dim 8).
Melodically, an augmented unison very frequently occurs when proceeding to a chromatic chord, such as a
secondary dominant, a
diminished seventh chord, or an
augmented sixth chord. Its use is also often the consequence of a melody proceeding in semitones, regardless of harmonic underpinning, for example
D,
D♯,
E,
F,
F♯. (Restricting the notation to only minor seconds is impractical, as the same example would have a rapidly increasing number of accidentals, written enharmonically as
D,
E♭,
F♭,
G♭♭,
A♭♭♭).
Harmonically, augmented unisons are quite rare in tonal repertoire. In the example to the right,
Liszt had written an
E♭ against an
E♮ in the bass. Here
E♭ was preferred to a
D♯ to make the tone's function clear as part of an
F dominant seventh chord, and the augmented unison is the result of superimposing this harmony upon an
E pedal point.
In addition to this kind of usage, harmonic augmented unisons are frequently written in modern works involving
tone clusters, such as
Iannis Xenakis'
Evryali for piano solo...
History
The semitone appeared in the music theory of Greek antiquity as part of a diatonic
tetrachord, and it has always had a place in the diatonic scales of Western music since. The various
modal scales of
medieval music theory were all based upon this diatonic pattern of
tones and semitones.
Though it would later become an integral part of the musical
cadence, in the early polyphony of the 11th century this wasn't the case.
Guido of Arezzo suggested instead in his
Micrologus other alternatives: either proceeding by whole tone from a
major second to a unison, or an
occursus having two notes at a
major third move by contrary motion toward a unison, each having moved a whole tone.
“As late as the 13th century the half step was experienced as a problematic interval not easily understood, as the irrational [
sic] remainder between the perfect fourth and the
ditone (
). In 5-limit just intonation, there's another semitone of 25/24 available between two major thirds (25/16) and a
perfect fifth (3/2), sometimes called a
just chromatic semitone because of its smaller size, but it's less common.
There are various other ratios which may function as a minor second. In 7-limit there's the
septimal diatonic semitone of 15/14 available between the 5-limit
major seventh (15/8) and the 7-limit
minor seventh (7/4). There is also a smaller
septimal chromatic semitone of 21/20 between a minor seventh and a fifth (21/8) and an octave and a major third (5/2). Both are more rarely used than their 5-limit neighbours, although the former was oft implemented by theorist
Henry Cowell, whilst
Harry Partch used the latter as part of his
infamous 43-tone scale.
Under 11-limit tuning, there's a fairly common
undecimal neutral second (12/11), but it lies on the boundary between the minor and
major second. In just intonation there are infinitely many possibilities for intervals that fall within the range of the semitone (for example the Pythagorean semitones mentioned above), but most of them are impractical.
Though the names
diatonic and
chromatic are often used for these intervals, their musical function isn't the same as the two meantone semitones. For instance, 15/14 would usually be written as an augmented unison, functioning as the
chromatic counterpart to a
diatonic 16/15. These distinctions are highly dependent on the musical context, and just intonation isn't particularly well suited to chromatic usage (diatonic semitone function is more prevalent).
Other equal temperaments
19-tone equal temperament distinguishes between the chromatic and diatonic semitones; in this tuning, the chromatic semitone is one step of the scale, and the diatonic semitone is two.
31-tone equal temperament also distinguishes between these two intervals, which become 2 and 3 steps of the scale, respectively.
53-ET has an even closer match to the two semitones as 3 and 5 steps of its scale. In general, because the two semitones can be viewed as the difference between major and minor thirds, and the difference between major thirds and perfect fourths, tuning systems that match these just intervals closely will also distinguish between the two types of semitones and match their just intervals closely.
Further Information
Get more info on 'Semitone'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://semitone.totallyexplained.com">Semitone Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
