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modcan - FMVDO


The FMVDO 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 12HP wide module

The most significant wave-shaping feature of the FMVDO 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, instead the FMVDO provides 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 an integer 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 Ratio can also be switched to provide non-integer ratios for inharmonic periodic sounds.

The FMVDO 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
  • Integer and non-integer modulation/carrier ratios for complex sub-harmonics switch selectable
  • 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
  • 12HP wide approx. 1″ deep
  • Waves:
  • Sine
  • Triangle
  • Saw
  • Square w/PWM
  • Double Pulse w/PWM
  • Random Stepped (with CV controlled variable interpolation)
  • 10 sample based wave tables

Frequency Range: 18 Octaves
High 10Hz-10kHz
Low .040Hz-40Hz
Output: +/-5V or 10Vpk-pk @1Kohms
Input CV 0-10V @100Kohms
Current: 80mA@+12V, 10mA@-12V

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 FMVDO 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 FMVDO modulating another VCO
SineLFO – FMVDO 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 FMVDO
SawLFO – Same as above using the FMVDO sawtooth
RandomLFO – Random wave from the FMVDO with varying amounts of interpolation. This provides smoothing between steps.
Audiomod – Audio rate FM of another VCO

Other modules by modcan | Touch-Sequencer | CV Record | Dual Delay | DualWave | Triple VCO | Quad LFO