Tracker organs date back many hundred years, although there are still modern tracker action instruments being constructed today. In a tracker organ, the organist presses keys and pulls stops which control the organ's pipes and couplers through a complex matrix of levers and valves. In a tracker organ, the valve, which admits air to the pipe in order to produce the sound, is directly controlled by the force of the organist's finger on the key. Some improvements have been made to the lever systems over the years, so that large amounts of pipes can be controlled without an excessive amount of force having to be exerted by the musician, but basically the organist must overcome the wind pressure resistance on each valve in order to open it and play the pipe. When many ranks are combined as a tracker organ is played, the keys generally become more difficult to depress. Another limitation of the tracker organ is that the console must remain relatively close to the pipes and wind chests. This is why most tracker organs have the console built as an integral part of the organ's case. There are a few exceptions, but generally, the console must be no more than a few feet from the pipes.
The valves which form the stops in tracker organs can be controlled directly (in a pure tracker) or they can be motorized as is being done in many newer tracker organs being built today. Motorized stop valves allow for the integration of modern combination actions to allow massive stop changes, by the organist, with the simple push of a button. In older organs, the stop valves are directly controlled by leavers attached between the stop valve and the respective stop knob on the console.
Because of the resistance to the player that results from wind at the pipe valve, tracker organs are generally quite different to the touch than are electrically controlled pipe actions. Because of this, tracker wind pressures, generally speaking, tend to be lower than the pressures found on large symphonic or theatre organs. In older tracker instruments, it is not uncommon to have noisy keys and pedals, especially when there is some wear to the pivot points throughout the lever system. While most modern tracker organs have electric blowers, there are still quite a few tracker organs in existence with their original pre-electricity era hand pumps still operational. Musicians who admire tracker organs sometimes delight in showing off these early hand-pumped instruments with the help of a colleague who pumps the air while the organist plays.
One may conclude that tracker organs are best suited to earlier forms of classical music. The instruments are often tuned to older scales of tuning in order to perform music as was played in earlier ages. A good tracker organ in the hands of a skilled organist, however, can play almost any literature, including popular Broadway and Rock music songs of the late Twentieth-century.
Some noted builders of tracker organs include: Aristide Cavaillé-Coll
of Paris, Hook and Hastings, Henry Erben, George Jardine, and Pilcher from America
in the 19th Century, and Fisk, Dobson, Redman and others who are still building
fine tracker instruments today. .