Studiologic Numa Organ - Manual (Page 7)

NUMA Organ by Studiologic® 7
What‘s behind NUMA Organ
E
How a tone wheel organ
works 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
consisting of a permanent bar magnet and a 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-
recorded audio file. But physical modelling calculates the formula
f(x)=[sin(x)]+[0,5*sin(2x)].
The graph of that calculation is shown below.
The sound engine of
NUMA Organ
Magnet
Spool
Tone wheel