VCDO

The VCDO 58B represents a new breed of sound generation for the modular environment. The primary design goal was to implement a variety of digital synthesis techniques and to combine them together in one module

The most significant wave-shaping feature of the 58B utilizes the technique referred to as Two-Operator FM, providing a wide variety of timbres from mellow bell like tones to complex distortion.

The inclusion of harmonically rich sample based wave tables extends the complexity of the FM effect comparable to multi-operator systems.

AM (Amplitude Modulation) is also available on-board as is standard Exponential FM using the Expo FM Jack

Conventional analogue VCOs are modulated with externally generated signals from LFOs and secondary VCOs etc.

Digital implementation of the VCDO 58B affords superior FM stability with internally generated, phase locked, sine table modulator.

The FM Index function controls the amplitude or depth of the modulation while the Ratio control tunes the modulator to a

rational frequency value relative to the carrier frequency.

Phase locking the modulator with the carrier produces beat-free timbres that retain spectral relationships over the entire frequency range.

The 58B includes standard VCO wave forms and adds several sample based wave tables. Pulse width modulation and hard sync are also supported.

Switch selectable quantized pitch tracking in semi-tone steps or non-quantized continuous frequency control with fine tune.

Firmware by DSP designer Eric Brombaugh.

Features:

32-bit NCO - 50 micro-Hertz resolution (no zippering)
Phase-locked FM/PM gives beat-free modulation
32 real-time voltage controlled modulation/carrier ratios
Fractional modulation/carrier ratios for complex sub-harmonics
Modulation index range from 0 to 314% for a wide range of continuously varying wave shapes.
Real-time voltage-controlled modulation index for subtle wave shaping
32-bit pseudo-random noise generator - won't repeat for 119
hours at highest frequency setting; longer at lower frequencies.
Voltage controlled selection of 16 wave forms
Quadrature secondary output at 90 degrees out of phase
Amplitude and Pulse width Modulation AM/PWM
Switch selectable quantized 1V/Oct input
Audio and LFO range frequency
Voltage controlled FM Index and modulation Ratio
Crystal tuning stability with +/-0.005% pitch tracking accuracy over 18 octaves

Waves:

Sine
Triangle
Saw
Square w/PWM
Double Pulse w/PWM
Random Stepped (with CV controlled variable interpolation)
10 sample based wave tables

Specs:

Frequency Range: 18 Octaves
High 10Hz-10kHz
Low .040Hz-40Hz

Output: +/-2.5V pk-pk @1Kohms
Input CV 0-5V @100Kohms

Demo MP3s

Sequence 1 -Stepping the Ratio during the sequence changes timbre

Sequence 2 -Same as seq 1

Fanfare -Sweeping the FM index with an envelope provides the "blat"

Car_Trouble -The VCDO in the low range, sweeping the index

Waves - Demo of the available waves

Ratio - Sine wave with different ratios.

Deep - Another low audio frequency demo

Slow - Longer noodle with filter and FM index modulated by the CV recorder

Pitchednoise - Random wave in a sequence

Bells - envelope applied to FM index using the sine wave

Harmonics -sweeping the ratio while keeping a fixed index

Plucky -a plucked effect

Tdreamish -Reminds me of a Tangerine dream sound.

Demos of the VCDO modulating another VCO

SineLFO - VCDO sine wave in LFO mode modulating a VCO
with varying FM to show the effect of changing wave shape.
The on-board AM is being used to control the amplitude of the VCDO

SawLFO - Same as above using the VCDO sawtooth

RandomLFO - Random wave from the VCDO with varying amounts of interpolation. This provides smoothing between steps.

Audiomod - Audio rate FM of another VCO