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ENV1 - Attack Decay


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The ENV1 is a simple, yet extremely useful, voltage controlled Attack / Decay envelope generator which can also spring into work as an interesting oscillator. The new Rev.2 version has improved internal circuitry along with the addition of Manual Gate button and End Out gate output.

There are three modes of operation, plus three rate ranges -
  • A/S/R Mode - Gated Attack / Sustain / Release - The output ramps and holds while the input Gate is high. When the Gate signal goes low again the output is decays to zero. If the Attack portion has not completed by the time the Gate goes back to low, the Envelope immediately changes to Release.
  • A/D Mode - Triggered Attack / Decay - The rising edge of an input Gate initiates a complete Attack/Decay cycle.
  • Loop Mode - Free Running - The output continually ramps up and down at rates determined by the attack and decay settings. (note that unlike usual VCOs the output signal is unipolar 0 to +10v)
  • 3-way Rate Switch - Fast/Mid/Slow - The Fast setting is primarily for audio rate oscillations (envelopes in this mode are too fast!). The Mid setting offers 'regular' envelope lengths and is suitable for higher-rate LFOs in loop mode. The Slow setting may prove too slow for envelope use, but can give very slow oscillations in Loop mode.
The Gate input has an internal comparator so any waveform going over c.+1v will produce a gate, so either traditional gates or other waveforms can be used.

The End Out socket provides a means to chain sequential events - the output is High (+10v) when inactive and goes Low (0v) for the entire cycle of the Envelope before returning High. To achieve 'sequential triggering' take the End Out of one Env into the Gate input of the next Env - as soon as the first Env completes, the second one will fire.

The Attack and Decay times are set along with independent modulation depth controls - these are polarizing to allow positive or negative effect (centre gives no modulation - but the dials do not have a centre-detent). Independent or inverted control of the two CV inputs proves a very useful feature. In Loop Mode the Attack / Decay controls allow interesting waveshaping Oscillator effects, moving the signal from triangle to saw for example. Note that the circuit uses Vactrols which result in quite a slewed control response, especially as slower times are dialed in.

An interesting further use is to feed an audio signal into the gate input - each Mode setting giving different results:
i) Audio SubDivision -> feed any oscillator into the Gate, set mode to AD and begin with Attack & Decay maxed -> this gives tracking of the oscillator rate. Now gradually turn down the attack and you'll hear the pitch dropping in harmonic divisions.
ii) Audio Sync-effects -> similar setup as before, but switch to Loop mode. Now adjust the Decay rate and hear audio oscillator sync.
iii) Filter-like effects can be achieved in ASR mode - adjust Attack for low-pass filtering and Decay to do something that sounds more like high-pass.

[Archive - Instruction Sheet (pdf) for rev.1 version - there are some differences, but the main thrust is the same]

Output: 0 to 10V
1 FW
Current: +ve 20mA / -ve 5mA
User Adjustments: None

Added on Saturday 03 January, 2009.