by Steve A

Hello, and welcome to the 64 Studio Aeolus primer. To configure Aeolus for the first time please refer to the Aeolus quickstart guide. This primer contains more information about how Aeolus emulates a real pipe-organ's sound and controls.

Organ stops in Aeolus

An organ stop is the "patch" which makes a particular sound. In a real pipe-organ, a stop is a family of pipes which make the same sound. The organist has a switch near the keyboard which allows them to patch each stop into the sound when needed.

In Aeolus, organ stops are represented as blue buttons. Each button normally contains two pieces of information: the name of the sound, and a number. The number represents the physical length (in feet) of the largest pipe - the bigger the number, the lower the pitch of the sound.

For example "Principal 8" is the Principal sound where the longest pipe is 8 feet long. Principal 4 is one octave higher and principal 16 is one octave lower. Therefore if Principal 8 and 4 are selected, every time a note is played, the organ will play two notes, each one octave apart.

Some Aeolus stops have fractions in their numbers; these stops play notes less than one octave from the note normally played - for example Quint 5 1/3 plays 5ths. Also, Aeolus has stops which play several high pitched harmonics to add brightness to the sound. In Aeolus, these harmonic stops are called "Cymbel VI" and "Mixtur".

Volume

Real pipe-organs cannot directly control the volume that each pipe produces. To overcome this limitation, organ builders will put some of the pipes in a special room with remotely controlled doors. The doors can be opened and closed to allow more or less volume to escape. The special room is called a "swell box" and the doors are controlled by a pedal at the organ console called a "swell pedal".

Aeolus controls volume through the "Instrum" window, or through the standard MIDI volume controller number 7 (see the MIDI section below).

Divisions

Large pipe organs often have multiple keyboards, allowing the organist to rapidly switch between the different keyboards to vary the tone and volume of the performance. Aeolus models a large organ which has three keyboards and a pedal board. It is helpful to imagine Aeolus as four organs in one. The four separate organs are called divisions, and are seen in Aeolus main window labelled P, I, II and III.

Division I

The volume of these stops cannot be controlled; in a real pipe-organ, these are the pipes which can be seen. The keyboard would be used when playing loud passages.

Division II

All of these pipes are enclosed in a swell box so volume can be controlled. The keyboard for this division would be the middle board.

Division III

All of these pipes are also in a swell box. In Aeolus, there are two swell boxes modelled, one for Division II and one for Division III - each has a separate volume control and audio settings. This division would be controlled by the top keyboard in the stack.

Division P - Pedal division

Pedal stops generally play the bass, and therefore tend to be the biggest pipes - so big that they are not normally put into a swell box. Due to the limited size of human legs, pedal stops are generally only the lowest two octaves.

Couplers

To make a really big sound, it is possible to "couple" the divisions together. In Aeolus the couplers are coloured brown. For example, if the I+II coupler is selected, the division I and division II organ stops can be played together from the Division I keyboard.

In single keyboard configurations, it is often best to configure the board as Division I and then use the couplers to introduce the division II and division III sounds.

Presets

Just like a real pipe organ, Aeolus also supports presets, which allow stop settings to be stored and rapidly recalled during the performance. With Aeolus you can select presets through the "Recall" button on the main window, or through MIDI keys sent on a separate control channel (see MIDI config below).

MIDI config

In the MIDI configuration window, three things can be configured:

Keyboards - which channel will receive the performance for each division

Divisions - which channels will contain MIDI CC7 (volume) to adjust the volume (swell) for division II and for division III

Control - which channel will receive notes 24 to 33 to recall presets 1 to 10

The Divisions and Control settings are optional.

Acoustic parameters of the organ

Through the "Audio" window, Aeolus allows the sound qualities of each division to be separately controlled. This also allows the stereo positioning of each organ to be altered, which makes the performance from Aeolus very realistic.

Further reading

www.kokkinizita.net/linuxaudio/
The Aeolus home page

www.geocities.jp/midi_organ_net/aeolus/
Musikun's excellent technical guide and sample performances

www.muse-sequencer.org/wiki/index.php/Aeolus
The Aeolus wiki

en.wikipedia.org/wiki/Pipe_organ
Background information from Wikipedia