A mixture is an organ stop

Organ stop

An organ stop is a component of a pipe organ that admits pressurized air to a set of organ pipes. Its name comes from the fact that stops can be used selectively by the organist; some can be "on" , while others can be "off" .The term can also refer...

, usually of principal tone quality, that contains multiple ranks of pipes

Organ pipe

An organ pipe is a sound-producing element of the pipe organ that resonates at a specific pitch when pressurized air is driven through it. Each pipe is tuned to a specific note of the musical scale...

. It is designed to be drawn with a combination of stops that forms a complete chorus (for example, principals of 8′, 4′, and 2′ pitches). The mixture sounds the upper harmonics of each note of the keyboard. The individual pitches in the mixture are not perceived by the listener; rather, they reinforce the fundamental pitches of the chorus, adding volume and brilliance to the sound. Historically, the mixture descends from the medieval Blockwerk concept, an organ in which there were no stops and all the ranks sounded simultaneously.

Variables affecting tone color

In addition to the standard concerns of voicing flue pipes

Organ flue pipe scaling

The subject of this article is technical in nature and requires an understanding of organ terminology. This is in the process of being rectified. Many of the terms used here are defined in the pipe organ article....

, Most mixture stops include only octave and fifth pitch levels; several historical mixtures include thirds, and some modern organs feature mixtures with other pitches such as sevenths and ninths.

The number of ranks per note in a mixture commonly increases as one ascends the compass of the keyboard. A mixture exhibiting this trait is referred to as progressive.

The frequency at which the various ranks in a mixture drop back by an interval (or break) as one ascends the compass determines to a great extent how the mixture sounds. If a mixture does not break, it is referred to as a harmonic mixture. Aristide Cavaillé-Coll

Aristide Cavaillé-Coll

Aristide Cavaillé-Coll was a French organ builder. He is considered by many to be the greatest organ builder of the 19th century because he combined both science and art to make his instruments...

 built many examples of mixture stops labelled "Plein jeux harmonique".

Mixture breaks

The composition of pitches

Musical tuning

In music, there are two common meanings for tuning:* Tuning practice, the act of tuning an instrument or voice.* Tuning systems, the various systems of pitches used to tune an instrument, and their theoretical bases.-Tuning practice:...

in a mixture may change (or break) several times across the compass of the keyboard. The "breaks" of a mixture involve the dropping out of a higher pitch at a given point within the keyboard's compass, and/or the addition of a lower pitch on the succeeding note.

For example, here is the break structure of a typical Great Fourniture IV:
Note Pitches on that note and above

C1 1’1/3 - 1’ - 2/3’ - 1/2’
C13 2’ - 1’1/3 - 1’ - 2/3’
C25 2’2/3 - 2’ - 1’1/3 - 1’
C37 4’ - 2’2/3 - 2’ - 1’1/3
C49 5’1/3 - 4’ - 2’2/3 - 2’
C C C C C C
1 2 3 4 5 6
C 1/16’ |------------+-----------+-----------+-----------+-----------/| 1 - C 1/16’
B | | | | | / | 1 - B
A# | | | | | / | 1 - A#
A | | | | | / | 1 - A
G# | | | | | / | 1 - G#
G 1/12’ |------------+-----------+-----------+-----------+------/----/| 2 - G 1/12’
F# | | | | /| / / | 3 - F#
F | | | | / | / / | 3 - F
E 1/10’ | | | | / | / / | 3 - E 1/10’
D# | | | | / | / / | 3 - D#
D | | | | / | / / | 3 - D
C# | | | | / |/ / | 3 - C#
C 1/8’ |------------+-----------+-----------+----/------/----/------/| 4 - C 1/8’
B | | | /| / /| / / | 5 - B
A# | | | / | / / | / / | 5 - A#
A | | | / | / / | / / | 5 - A
G# | | | / |/ / |/ / | 5 - G#
G 1/6’ |------------+-----------+------/----/------/----/------/----/| 6 - G 1/6’
F# | | /| / /| / /| / / | 7 - F#
F | | / | / / | / / | / / | 7 - F
E 1/5’ | | / | / / | / / | / / | 7 - E 1/5’
D# | | / | / / | / / | / / | 7 - D#
D | | / | / / | / / | / / | 7 - D
C# | | / |/ / |/ / |/ / | 7 - C#
C 1/4’ |------------+----/------/----/------/----/------/----/-------| 7 - C 1/4’
B | /| / /| / /| / /| / | 8 - B
A# | / | / / | / / | / / | / | 8 - A#
A | / | / / | / / | / / | / | 8 - A
G# | / |/ / |/ / |/ / |/ | 8 - G#
G 1/3’ |-------/----/------/----/------/----/------/----/------------| 8 - G 1/3’
F# | / /| / /| / /| / | | 7 - F#
F | / / | / / | / / | / | | 7 - F
E 2/5’ | / / | / / | / / | / | | 7 - E 2/5’
D# | / / | / / | / / | / | | 7 - D#
D | / / | / / | / / | / | | 7 - D
C# | / / |/ / |/ / |/ | | 7 - C#
C 1/2’ |/----/------/----/------/----/------/-----------+------------| 7 - C 1/2’
B | / /| / /| / | | | 5 - B
A# | / / | / / | / | | | 5 - A#
A | / / | / / | / | | | 5 - A
G# | / / |/ / |/ | | | 5 - G#
G 2/3’ |/------/----/------/----/-----------+-----------+------------| 5 - G 2/3’
F# | / /| / | | | | 3 - F#
F | / / | / | | | | 3 - F
E 4/5’ | / / | / | | | | 3 - E 4/5’
D# | / / | / | | | | 3 - D#
D | / / | / | | | | 3 - D
C# | / / |/ | | | | 3 - C#
C 1’ |/----/------/-----------+-----------+-----------+------------| 3 - C 1’
B | / | | | | | 1 - B
A# | / | | | | | 1 - A#
A | / | | | | | 1 - A
G# | / | | | | | 1 - G#
G 1’1/3 |/-----------+-----------+-----------+-----------+------------| 1 - G 1’1/3
C C C C C C
1 2 3 4 5 6

External links

• Data outflows and graphics of mixtures L'Hydraule (the example above without outflow).
• Study of the Aristide Cavaillé Coll's pipework. Laurent Plet.