Doepfer A-191 Shepard Generator/16xMIDI-CV Interface (no longer available) - Manual (Page 14)

A-191 MCV 16 System A - 100 doepfer
14
5.2 In- / Outputs
! CV outputs
The CV output sockets ! send out sawtooth and
triangle waveforms. The number on each output
refers to the amount of phase displacement, in de-
grees:
S0 • S45 • S90 • S135 • S180 • S225 • S270 • S315
Sockets S0 to S315 output the sawtooth waveforms.
T0 • T45 • T90 • T135 • T180 • T225 • T270 • T315
Sockets T0 to T315 output triangle waveforms.
5.3 User examples
Generating "Shepard Tones"
The Shepard Tone is a psycho-acoustic phenome-
non, that gives the impression of a continuously rising
or falling tone.
Fig. 6 shows the sort of patch needed. The Shepard
generator’s sawtooth waveform controls the pitch of
eight VCOs, all with identical settings, while the tri-
angle outputs control 8 VCAs - one for each VCO. To
hear the effect properly, the outputs from the VCAs
must be patched to two mixers (2 x A-138).
The Shepard effect is pretty mind-blowing, because it
seems to be producing the impossible - a never-
ending upward (or downward) sweep of the note.
Although it seems almost miraculous, there’s nothing
mysterious about how it works. The Shepard tone
contains a large amount of octave-related harmonics
across the whole audio spectrum, all of which rise (or
fall) together. The harmonics towards the low and high
ends of the spectrum are gradually attenuated the
closer they get to the ends, while those in the middle
have maximum amplification.