Mixture (music)

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A mixture is an organ stop of principal tone quality that contains multiple ranks of pipes. 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. Because a mixture's function is to add color to the tonal ensemble, multiple-rank solo stops (such as the Sesquialtera or the Cornet) are not considered mixtures.

[edit] Variables

Variables affecting a mixture's tone color and usage include:

1. Types of pitches included
   1. Octaves
   2. Quints
   3. Other pitches
2. Lowest pitch at C1 (tessitura)
3. Type and position of pitch breaks
   1. Octave breaks
   2. Fourth or fifth breaks
   3. Other breaks
4. Number of ranks per note
   1. Constant
   2. Variable
   3. Balance between number of unison pitched pipes and other pitches
5. Scaling of the pipes
   1. Diameter scale
   2. Halving ratio
   3. Parallel scaling of ranks
   4. Mixed scaling of ranks
6. Mouth widths
7. Voicing style

[edit] Mixture breaks

The composition of pitches 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′