10.6

655Logic Pro Instruments
Despite characteristics such as key clicks, variable intonation, distortions, and crosstalk
(all of which Vintage B3 emulates), playing a single note, with a single register, results
in a pure sine tone. Mixing sine tones results in more complex harmonic spectra; this is
known as additive synthesis. Organs—even pipe organs—can be regarded as additive
synthesizers. Several limitations should be considered before viewing the instrument in this
way. These limitations, on the other hand, constitute the charm and character of any real
musical instrument.
The naming of the draw bars is derived from the length of organ pipes, measured in feet (').
This naming convention is still used with electronic musical instruments.
• Halving the length of a pipe doubles its frequency.
• Doubling the frequency results in an upward transposition of one octave.
The lowest register—16’ (far left, brown draw bar)—and the higher octave registers—8’,
4’, 2’, and 1’ (white draw bars)—can be freely mixed, in any combination. 16’ is commonly
described as the sub-octave. With the sub-octave regarded as the fundamental tone, or
first harmonic, the octave above 8’ is the second harmonic, 4’ the fourth harmonic, 2’ the
eighth harmonic, and 1’ the sixteenth harmonic.
With the 51/3’ register—the second brown draw bar—you can add the third harmonic. This
is the fifth above the 8’. Basically, the draw bars are arranged by pitch, with one exception.
The second draw bar (51/3’) sounds a fifth higher than the third draw bar. See The residual
effect for an explanation.
The 22/3’ register generates the sixth harmonic, 13/5’ the tenth harmonic, and 11/3’ the
twelfth harmonic.
An electromechanical tonewheel organ offers the choice of the following registers/
harmonics:1 (16’), 2 (8’), 3 (51/3’), 4 (4’), 6 (22/3’), 8 (2’), 10 (13/5’), 12 (11/3’), and
16 (1’). As you can see, the harmonic spectrum is nowhere near complete. This is one of
the main reasons for the common practice of using overdrive and distortion effects with
electromechanical tonewheel organs—they enrich the harmonic spectra by generating
more harmonics.
Note: 22/3’ is the fifth over 4’. 13/5’ is the major third over 2’. 11/3’ is the fifth over 2’. In
the bass range, this can lead to inharmonic tones, especially when playing bass lines in a
minor key. This is because mixing 2’, 13/5’, and 11/3’ results in a major chord.
The residual effect
The residual effect is a psychoacoustic phenomenon. Human beings can perceive the
pitch of a note, even when the fundamental tone is completely missing. If you pull out all
registers of a draw bar organ, except for the fundamental—16’—you’ll still perceive the
same pitch. The sound becomes thinner, with less bass and less warmth, but the pitch
remains the same.
If human beings didn’t hear this way, it would make listening to music on a small transistor
radio impossible. The tiny speaker of a small radio can’t accurately play back the
fundamental tone of the bass line because this frequency is far below the range that the
speaker can reproduce.
Setting draw bar registrations often involves this psychoacoustic phenomenon. In the
lower octaves, mixing the 8’ and 51/3’ sine draw bars creates the illusion of a 16’ sound,
although the lower frequency is missing.