What's Behind Numa Organ; How A Tone Wheel Organ Works; The Sound Engine Of Numa Organ - Studiologic Numa Organ Operation Manual

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In an original tone wheel organ, which was the model for NUMA

Organ, 91 steel wheels with lobes rotate in front of a pick-up con-

sisting of a permanent bar magnet and a spool.

Tone wheel

Magnet

Spool

Because of the tone wheels' shape and rotation, the magnetic field

in the pick-up changes periodically and generates a sine wave. With

8 different tone wheel shapes and 12 different gear trains 91 sine

frequencies are generated. This is independent of playing a note or

not. Corresponding to the principle of additive synthesis, those 91

frequencies are the base for creating different sound timbres.

By means of a complex circuit layout the sound is mixed via nine

drawbars and nine electrical contacts under each key. In this way

a tone wheel organ is able to create hundreds of perceivably

different sound timbres from just 91 generated sine frequencies. In

theory more than 380 million timbres are possible, but lots of those

timbres sound similar or are musically the same, for example an

octave shift.

To generate a sound, NUMA Organ uses physical modelling. With

this technique a mathematical formula is used to describe the

physical behaviour of the tone wheel organ. The physical model

also calculates the impact and interaction of parameters on each

other.

A good example of this is the parameter Leakage. As

mentioned, a tone wheel organ generates all frequencies

at the same time, independent of whether a key is pressed or not.

With Leakage you can control from your NUMA Organ what we

might call the parameter "cross-talk of physically close together

tone wheels".

The following example shows how the theory of physical modelling

really works:

To generate a "tonic keynote plus its upper octave with the half

level", a sample based synthesizer would simply play a pre-re-

corded audio file. But physical modelling calculates the formula

f(x)=[sin(x)]+[0,5*sin(2x)].

The graph of that calculation is shown below.