Many combinations of perforation may be opened so that different volumes can be achieved, this is where proper roll editing is imperative. Usually these systems work in conjunction with bass and treble lift pneumatics that further increase or decrease the sound level by holding the hammers closer to the strings to soften the blow or in their normal rest position if fuller sound is desired. As each perforation crosses the inlet, a pneumatic is caused to collapse, usually opening and closing a knife valve to allow more or less suction into either side of the stack being controlled, making the note play louder or softer depending upon which pneumatic is activated. The dynamic system is controlled automatically by two sets of 4 or more perforations in a reproducing roll, one set for bass, one set for treble, opening corresponding inlets in the reproducing tracker bar. Each side of the split stack has it's own dedicated intensity mechanism. The stack is invariably split, by way of an internal wall in the stack vacuum chamber, into bass and treble. To achieve this, a complex series of intensity valves and pneumatics are employed to restrict, in various combination of degrees, the vacuum flow out of the stack. The reproducing player piano seeks to replicate the original touch of the pianist.
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