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Spectral Audio Neptune

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The Neptune is a purely analog synthesizer with MIDI control. It offers special features and is simple to use because it has a button or switch for each parameter. The audio input enables to process external signals.

The basic principle of the Neptune corresponds to the proven analog synthesizer principle equipped with VCO, VCF, VCA, envelope generator and LFO. This principle is called subtractive synthesis.To make the Neptune suitable for MIDI, an additional MIDI to CV converter is applied which converts the MIDI signals into analog signals. These control the VCOs, the filter, as well as the envelope generator.

The raw material for the sound is provided by the VCOs (Voltage Controlled Oscillator) in the form of a sawtooth or rectangular signal as well as the noise generator (for effects such as wind and thunder sounds). VCO2 is synchronised by the VCO1 with the SYNC switch. The sound becomes interesting when the TUNE regulator of the VCO2 is turned (or modulated by the LFO VCO2), resulting in a typical "Sync-Sound". By means of the external VCO input, other sounds can also serve as raw material.
The ring modulator multiplies the signals of the two VCOs and this significantly amplifies the beats (frequency difference).

The SLIDE regulator determines the time balance from one note to another and is valid for both VCOs and the suboscillator. Afterwards, the signal flows through the voltage-controlled filter (VCF=Voltage Controlled Filter), within which certain frequency ranges are suppressed. The lowpass filter allows low frequencies to pass and suppresses the high ones, the highpass filter lets high frequencies pass and suppresses the low ones. The frequency from which the signals are suppressed is called the limit or cut-off frequency. In the Neptune, this is formed by various sources:

1. CUTOFF frequency regulator

2. ENV MOD regulator (influence of the envelope curve on the cut-off frequency)


The KEYFOLLOW is always 100%. It causes the cut-off frequency to increase on higher notes so that the audible freqency band always remains the same. Moreover the filter can be used as an oscillator, if the resonance is set to the maximum. The resonance forms a feedback of the output to the input of the filter and causes an amplification of the frequencies around the cut-off frequency.

Afterwards the signal reaches the distorter, witch provides two different ways of distortion. Before the signal leaves the Neptune, it arrives at the VCA (Voltage Controlled Amplifier). Here the input signal is multiplied by a control signal. In this way, the volume can be influenced by a control signal coming from the envelope generator.

The LFO is particularly designed in the Neptune. The oscillator is either freely controllable or fixed to the MIDI to CV converter. In this case it works as a suboscillator. Note: When using the LFO in a freely controllable way, the description at the oct-switch does not apply. It is however possible to adjust a coarse frequency. Using its signal, the pitch from VCO1 and VCO2 and thus the cut-off frequency of the filter can be modulated. If the MIXER switch is on, the LFO output is directly audible. In this case, the MOD pot is the volume.

The rotary switch allows 5 different signal forms to be selected from. Additonaly, the VCO 2 can be used as a modulation source. The MIDI SYNC switch allows the LFO to be sycronized by the MIDI clock.

The envelope generator determines the chronological sequence of the volume after receiving a sound command. The MIDI to CV converter then issues a gate signal (+5V) starting the sequence of the envelope generator. The gate signal remains active at +5V until the 'sound off' command comes, i.e., when the key is released:

Technical Specifications
Type: Analog
Synthesis: Subtractive
Oscillators: 3
Waveforms: Pulse, Saw Up, White Noise
Osc Modulation: Continuous Controller, Envelope, Knob, LFO, Ring Modulation, Sync Hard
Envelopes: 1
Evelope Paramerters: Attack, Decay, Sustain, Release
Filters: 1
Types: 24dB Slope (4-pole), High Pass, Low Pass, Resonance
Filter Modulation: Envelope, Knob, LFO
LFO: 1
LFO Parameters: Noise, Sample & Hold, Saw Up, Triangle
Polyphony & Tuning
Polyphony: 1
Tuning: Standard
Modes: Mono
Patches RAM: 1
Distortion and ‘Fuzzer’ Effect
Case: Rack
Rack Size: 19", 2U, Full
Controls: Buttons, Knobs, Switches, Modulation 1/4" Jacks
Audio Output Connections: 1/4" Phone Jack, Mono Out
Audio Output Count: 1
Inputs: 1 x 1/4" input
CV Ports: CV IN, CV OUT, Gate In, Gate Out
Year Released: 1999
Year Discontinued: 2003
Manuals & Documents

Product Links
Company Product Sites:
[+] www.spectralaudio.ch
Used Price: $600 - convert
References & Sources

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