This is a complete list of the registers provided on the Carl Frei 90-key street organ scale. I have listed them in their relevant sections of the organ. The ones I have incorporated into my organs are listed first, then the ones treated as "spare" keys.
Violin: Two ranks of narrow scaled open pipes speaking together exactly in tune with each other.
Bourdon: Two ranks of stopped flutes, with one rank tuned slightly sharp to give an undulating effect. The rate of the undulations is faster in the treble than it is in the bass, but not in direect relation to the pitch of the note. Over the two octaves the pitch quadruples, but the celeste undulations may barely reach double. The tuning is done purely to the ear and preference of the tuner, i.e. an electronic tuner cannot be used.
Celeste: Two ranks of violin pipes playing together. One rank is tuned to the pipes in the violin register, and the other one is tuned slightly sharp, like the bourdon celeste, tuned by ear for best effect.
Piccolo: One rank of open flutes playing one octave higher than the violins.
Tremulant: This acts on the melody action to rhythmically open and shut the action wind to the pipe chests. It creates the most recognised "Dutch" sound.
Bifoon: [not present on my organs] One rank of bourdon pipes at 16-foot pitch (one octave lower than the violins. A misnomer, but that's what Carl Frei used.
Unda maris: Two ranks of violin pipes at 16-foot pitch, one octave lower than the equivalent ranks on the melody. One rank is tuned "straight" and the other is tuned sharp for a "celeste" effect.
Bifoon: Two ranks of bourdon pipes, one octave lower than the melody violin. One rank is tuned straight, and the other is tuned sharp for a "celeste" effect.
Cello: One rank of wide-scaled string pipes.
Tremulant: The counter-melody tremulant acts on pipe wind, NOT action wind as on the melody. The effect is not so harsh, and allows the chest pressure to "bleed" through the playing pipes instead of shutting them off suddenly.
Baritone: [Not present on my organs] This is a box reed, similar to the saxophone on a fair organ.
Trombone: One rank of bass reeds of the trumpet type. To be used sparingly in street organ music.
Bass Cello: [Not used on my organs] One rank of violin-type pipes playing at the same pitch as the bass bourdons. The "cello bass" rank on my organs play one octave higher and are not register controlled.
Bass drum: Normal for any large organ. The bass drum action also often operates a cymbal (and/or bell ringers).
Snare drum: Two beaters operate the drum from two separate keys in the music. A woodblock is sometimes used with its own action, but operated from the share drum keys via a changeover action, so the woodblock works in quiet music while the drum operates in loud music.
Cymbal: [Not used on my organs] This separate key can be used for the cymbal instead of the bass drum action.
Triangle: [Not used on my organs] Single key for one or two triangles, or even bell ringers.
3 spares: Keys not allocated on the 90-key scale. They can be used for anything, so long as the music arranger is aware of their existence when arranging for a particular organ.