Spectral Audio ProTone

Spectral Audio ProTone Image
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The ProTone is a true analog synth from the mid-nineties for the modern MIDI studio. It is monophonic and features two analog oscillators, a beefy resonant filter, flexible LFO, MIDI and CV/Gate control, and a simple intuitive hands-on layout with every control parameter accessible from the front panel knobs and switches.

Each oscillator features saw and pulse waveforms with independent waveform selection, tuning and level. White Noise is also available from VCO1. The oscillators can be sync'd and Ring Modulation can also be dialed in. The filter section allows for either high or low pass filtering and 12 or 24 dB/oct slopes with the usual cutoff and resonance knobs. A fairly standard ADSR envelope can be applied to the voltage-controlled amp, but there's only a decay envelope (Accent) for the filter. The LFO is quite flexible, with six wave shapes plus random, noise or external input. The LFO can be set to modulate VCO1, VCO2, Pulse-Width on VCO1, filter cutoff and panning. A few remaining controls include a Panner, and Slide (portamento) effect.

The ProTone features MIDI I/O and traditional CV/Gate I/O for use with vintage gear. A little too much like vintage gear, however, the Pro Tone does not have on-board program memory. But with such a basic synth architecture and no hidden menus or parameters, the ProTone is a hands-on tweaker's synth - full of fat analog bass and synth sounds with a squelchy filter and competent LFO. Additional features include external VCO and LFO inputs, MIDI controlled volume and frequency cutoff, velocity sensitivity, and stereo outputs. The ProTone makes a cost effective, reliable and unique alternative to many other older vintage dual-VCO analog mono-synths.

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Demos & Media

Audio Clip 1 Demo bass and synth sounds. From Future Music CD issue 51.
Audio Clip 2 Demo submitted by Moimir Papalescu.


Polyphony - Monophonic
Oscillators - 2 analog VCOs (Sawtooth and Pulse Waves); White Noise Generator; True Ring modulator
LFO - 1 (Rectangle, Impulse, Triangle, Sawtooth, Sinus, Noise and Random); Wide LFO Range: 0.005 ... 3800 Hz; LFO Targets: VC01, VC02, Pulse Width of VC01, Cutoff and Panorama
Filter - High and Lowpass Filter with Resonance, Selectable 12 or 24 dB per Octave, Accent (Decay Envelope for the Filter)
Effects - Slide (portamento)
Memory - None
Keyboard - None
Arpeg/Seq - None
Control - MIDI In/Out, CV+Gate In/Out
Date Produced - 1996-2001


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Reviewed August 2008.