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What is the duo-art?
The Duo-Art was the reproducing piano system produced by the Aeolian Corporation, and like the Ampico and Welte was designed to reproduce an actual performance by a pianist which had been recorded on special equipment, with the note intensity values being encoded in (essentially) four-bit binary code within Duo-Art rolls: four bits for the theme intensity and four bits for the accompaniment, with theme and accompaniment being assigned to bass and/or treble as require. Duo-Art rolls are of standard width and spool design but have additional coding in the margins. There were actually three main variants of the Duo-Art system, two of which were capable of being used as true reproducing pianos, with the third being essentially a pedal pianola with enhanced expression:
The electric-only Duo-Art: this is designed to operate purely as a reproducing piano, though with some capability for playing non-reproducing rolls without expression.
The Pedal-Electric Duo-Art (PEDA): this is a dual-purpose instrument capable of being configured either to operate electrically as a reproducing piano, or to be used as a conventional pedal-operated player piano. The PEDA makes for a very versatile and desirable instrument; it was however primarily a product of Aeolian in the UK and is virtually unknown in the USA where only the electric-only Duo-Art (and standard pedal-operated pianolas) were available.
The pedal-only Duo-Art (Pedal Duo-Art often known as the half Duo-Art): this is very similar to a conventional pedal-operated pianola but instead of a standard expression box it has a single Duo-Art regulator as shown in the technical explanation below. This controls the accompaniment level (in other words, the non-theme notes forming the background to the music) while the theme is automatically picked out at the level controlled directly by the pedalling of the pianolist. It was arguably something of a ploy to create a market for the expensive Duo-Art rolls among people who could not afford a full electric or pedal-electric instrument.
The following sections explain how the Duo-Art system reads the notes from the roll and plays them at the level specified in the special coding in the roll margins.
How the Duo-Art works: introduction
The Duo-Art system has a single expression box which supplies both halves of the player stack at two alternative levels of playing: "theme" (for bringing out the melody or foreground of the music) and "accompaniment" (background level of playing). The expression box has suction regulators for setting both of these levels, and a valve system for connecting either or both halves of the stack to the theme regulator (by default they are both driven from the accompaniment regulator).
The diagram above shows how both halves of the stack are connected to the single expression box, and the picture below shows the inside of a Pedal-Electric Duo-Art reproducing piano with the main components labelled.
How the duo-art expression box works
The key component of the Duo-Art system is the expression box which controls the playing of both the bass and treble halves of the player mechanism (the “stack”). It consists of two suction regulators (one for theme, one for accompaniment), each of which is operated by a lever which is pulled down via a control rod, with the movement being provided by "accordion pneumatics", one of which is visible in the lower part of the picture. The "accordion" pneumatic has four sections which can collapse in by differing amounts (1/6", 1/8", 1/4", 1/2") to give sixteen possible combinations. This gives sixteen basic levels of playing volume. In practice, various tricks, and other features of the Duo-Art system not explored here, were used to give even more subtlety.
The following sequence of diagrams explains how the expression box works; click on the left and right arrow buttons to move forward or backward through the sequence. The sequence is best viewed on a desktop or laptop PC as it is not optimised for small screens e.g. smartphones. [We are working on it!]
Here is a video explaining in detail how the various perforations control the theme and accompaniment suction and set the expression intensity to the sixteen different levels