How this organ works

An organ has no volume from your fingers — a key just opens a pipe, and the pipe speaks at one loudness until you let go. Everything expressive happens elsewhere.

Drawing stops

Each knob opens a set of pipes. Pull out more than one and they all sound together on every key you press. The number is the pitch: 8′ sounds where you play, 4′ sounds an octave higher, 16′ an octave lower, 2′ two octaves up. The 2⅔′ Nazard sounds a fifth above — on its own it is strange, but added to an 8′ it thickens the tone.

Start with Open Diapason 8′ alone. Add Principal 4′ for brightness, Bourdon 16′ for weight, Trumpet 8′ when you want the room to notice. Stopped Flute and Viola da Gamba are quieter colours for slow music.

Swell and Church

Swell is the shutter pedal: it opens and closes louvres in front of the pipes, which is the only real volume control an organist has. Church sets how much cathedral you are sitting in.

Tremulant

Wavers the wind supply for a gentle pulsing. Traditionally used sparingly, on soft stops.

Playing

Click or tap the keys, or use the computer keyboard — Letters shows which key is which. The lower row starts on C, the upper row an octave above. Keys sets how much of the compass is on screen; with a shorter view, the arrows move it up and down. Focus fills the whole screen, which is the only way to get a full-screen keyboard on a phone.

Scores

Pick a piece and the knobs move to a registration organists commonly use for it — full principal chorus with the reed for the Toccata and Fugue, a single soft flute for a chorale prelude. Change any of them and press Play for a different instrument. Tempo stretches the speed. Sheet music opens the printed score in a new tab.

Scores come from the Mutopia Project. Most are public domain; BWV 536 and BWV 544 are CC BY-SA 3.0.