Automatic SATB Part-Writer

Voicing

In SATB settings, all voices fit within the following default ranges. Solid noteheads represent the default comfortable range (tessitura).
Default ranges for keyboard style are as follows:
Voices don't cross: the bass is never higher than the tenor, the tenor is never higher than the alto, the alto is never higher than the soprano.
In SATB style, upper voices (tenor, alto, and soprano) are never more than an octave apart. The bass and tenor are never more than P12 apart.
In keyboard style, upper voices together never span more than an octave.

The root of root-position major and minor triads is doubled by default. The user has the option to allow doublings of the fifth and/or third in root-position triads. (See below for situations where the third may be doubled regardless of user settings.)
Leading tones are never doubled.
Any member of a first-inversion triad may be doubled, with the exception of tendency tones.
The bass (third) of N6 is doubled. The root of the less-common N53 is doubled.
The bass (fifth) of second-inversion triads is doubled.
In a deceptive progression (V-vi and related), the third of vi may be doubled. This applies to analogous progressions involving a dominant chord moving to a triad whose third is the expected root: for example, V7/vi-IV. As it is often necessary for correct partwriting, this doubling may be used whether or not the user has selected the option to allow doubled thirds.
Root-position seventh chords are either complete or spelled without the fifth, in which case the root is doubled.
Chordal sevenths are never doubled.
In V7-I, if V7 is complete, the I chord may omit the fifth and triple the root. This is possible in secondary relationships, too.
The third of a root-position triad may be doubled following viio7, as a logical consequence of tritone resolution. This doubling may be used whether or not the user has selected the option to allow doubled thirds.
Inverted seventh chords are always complete.
The tonic pitch is doubled in It+6.

Voices may not overlap. In the following example, the bass overlaps the tenor by moving to a note higher than the note that the tenor just left:
Parallel fifths and octaves are not allowed.
Successive perfect fifths or octaves by contrary motion are not allowed.
Direct or hidden fifths and octaves. If the bass and soprano move to a perfect fifth or octave by similar motion, the soprano should move by step. There is no restriction if other pairs of voices are involved.
Unequal fifths. Motion from d5 to P5 involving the bass is avoided unless the soprano and bass move in parallel 10ths. No restrictions are placed on this motion if the bass is not involved.

Chordal sevenths are not approached by downward skips.
Chordal sevenths ordinarily resolve down by step.
In the progression V43-I6, the seventh may move up by step if there are parallel tenths between bass and soprano.

The leading tone normally resolves up by half-step to the tonic.
In V7-I, the leading tone may move down to the fifth of I if it is in an inner voice. This allows both chords to be complete.
In V-vi, the leading tone may move down by step if it is in an inner voice.
The leading tone moves down by half step in progressions such as V7/V-V7.
The leading tone in iii need not move to tonic.

Leaps larger than a P5 are avoided in the upper voices.
Leaps larger than a P5 may appear in the bass, but cannot exceed an octave. Descending M7/m7 leaps are avoided, but the characteristic descending d7 is permitted.
In the upper voices, successive leaps in the same direction will be triadic.
Augmented melodic intervals are not allowed in the upper voices. Some augmented intervals can appear in the bass.
Diminished melodic intervals are possible. The diminished octave is not used.
In the bass, two leaps in the same direction will not cover more than an octave.
After a leap larger than a P5, the bass changes direction.
Octave leaps in the bass are prepared with the same pitch or by contrary motion.
Leaps of a seventh in the bass are prepared by contrary motion.
The bass repeats its pitch or changes direction after a leap of an octave.