Understanding Organ Stops By Dr Steven Nisbet OAM After you have played a number of pipe organs, you quickly realise that all organs are different. However, there is a consistency among all organs (pipe and digital) and that is the system for naming the stops. Because of this system, organists become familiar with stop names and can predict what sort of sound each stop will make. It helps to realise that there are four families of sounds that pipes make. The families are: 1. Principals or Diapasons, 2. Flutes, 3. Strings, and 4. Reeds. The first three families have flue pipes (like a fireplace flue) and the sound is produced by air vibrating in the pipe, like an orchestral flute. Pipes in the 4th family have brass reeds at the foot of then pipe and these brass reeds vibrate to produce the sound, like a clarinet or oboe. Let me demonstrate the different families of stops on this Allen digital organ.

Principals & Flutes Strings Reeds Diapasons (Sweet sounds, (Thin sounds, that (Sounds that imitate (The characteristic that imitate the imitate stringed orchestral reed & organ sound) orchestral flute) instruments) brass instruments) Stop names Stop names Stop names Stop names Principal 8’ Flute 8’ Dulciana 8’ Clarinet 8’ Principal 4’ Suabe Flute 8’ Salicional 8’ Oboe 8’ Principal 2’ Clarabella 8’ Viola da Gamba 8’ Cromorne 8’ Diapason 8’ Lieblich Gedact 8’ Viole 8’ Trumpet 8’ Open Diapason 8’ Bourdon 8’ Vox Celeste 8’ Cornopean 8’ Octave 4’ Hohl Flute 8’ Gamba 8’ Tuba 8’ Twelfth 2 2/3’ Harmonic Flute 4’ Cello 8’ Orchestral Trumpet 8’ Fifteenth 2’ Wald Flute 4’ Violin Diapason 8’ Spanish Trumpet 8’ Nineteenth 1 3/5’ Nazard 2 2/3’ Keraulophon 8’ Clarion 4’ Mixture IV Piccolo 2’ Gemshorn 4’ Contra Fagotto 16’ Sharp Mixture V Bourdon 16’ Geigen Principal 4’ Ophicleide 16’ Fourniture V Sub-bass 16’ Fugara 4’ Bombarde 16’ Double Diapason 16’ Bass Flute 8’ Violone 16’ Posaune 16’ Major Bass 16’ Tibia 8’ Violoncello 8’ Contra Posaune 32’

Beside each name is a number. This number indicates the speaking length (in feet) of the longest pipe in the rank. The longest pipe is about 8’ long and it is bottom C. Middle C on an 8’ stop on an organ keyboard has the same pitch as middle C on a piano. A 4’ stop sounds an octave higher than the 8’ stop, and a 2’ stop sounds an octave higher than that. A 16’ stop sounds an octave lower than an 8’ stop. These numbers are all powers of two: 2’, 4’, 8’, 16’, and 32’. However, some stops have numbers which are not powers of two. These indicate that they are Mutation stops. Rather than sounding in octaves, Mutations sound at intervals of fifths & thirds above the note played, – e.g. Twelfth 2-2/3’ (fifths), Nazard 2-2/3’ (fifths), Tierce 1-3/5’, (thirds), and Larigot 1-1/3’ (fifths). Mutation stops are used to fill out the sound, or to make a special effect with a solo melody. Next, some stops have Roman numerals beside them. They are the Mixture stops and the Roman numeral indicates the number of pipes that sound for every note played. The pipes sound at high pitches (octaves, fifths & thirds). For example, Mixture III has three pipes sounding for each note played. Plein Jeu IV has four pipes sounding for each note played. Other examples of mixtures are Sesquialtera II, Fourniture IV, Cornet V. Other organ stops Couplers: A coupler connects one division of the organ to another. For example, the Swell to Pedal coupler connects the Pedals to the Swell manual, so that a note played on the Pedals also sounds on the Swell manual. The Swell to Great coupler connects the Swell manual to the Great manual, so that a note played on the Great manual also sounds on the Swell manual. Tremulant: A tremulant varies the wind supply to the windchest and causes the volume and pitch of the sound of the pipes to fluctuate, producing a tremolo or vibrato effect. Summary In conclusion, this video has been about organ stops, the four families of sounds and the system used to name the stops. • The families are: 1. Principals or Diapasons, 2. Flutes, 3. Strings, & 4. Reeds. • Some stops sound in octaves, others sound in fifths and thirds. • The couplers connect two divisions of the organ. • The tremulant produces a vibrato effect. Getting to know the stops on an organ is time-consuming, but it is well worth the time. I encourage you all to spend time at the console pulling out the stops and listening to the sounds they make. Listen for the quality of the sound, the pitch and the volume of sound that each stop makes.