Motivation

ENV_Follower_Front_small

This envelope follower was first build for my Shakuhachi 2 Synth project. But it is useful for any other input signal which you want to derive a control voltage from. It provides a gate and a trigger signal as well. The envelope follower is used to detect the amplitude variations of the incoming signal and produces a control voltage that resembles the variations in the input signal. The gate and trigger signal is derived from the input signal as well. You can vary the threshold to determine at what minimum signal level the gate goes high and the trigger fires. Gate level is +5V. Trigger level is +5V/1msec.




Specs and features


Implementation

Schematic

ENV Follower schematic

ENV Follower schematic

Description:

The incoming signal is rectified with a precision full wave rectifier (IC2C, IC2D). Then feed to a low pass filter for smoothing (IC2B). The given filter values here are optimized for use with the Shakuhachi, but can easily changed to your needs. The filter values affect the ripple and the timing of the output control voltage. The gate and the trigger signal is derived from the filter output with means of a comparator (IC3C). You can adjust the sense level with the threshold potentiometer. The gate is indicated with a LED. The trigger pulse is derived from the gate with an differentiator (IC3D). The other circuitry does some level shifting and buffering.


CV output scope picture

ENV Follower scope picture

ENV Follower CV output from a VCA with square input signal

The picture above shows the control voltage of the envelope follower following a signal of 200Hz sine wave from a VCA (purple line) with a square control voltage (blue line).


ENV Follower scope picture

ENV Follower CV output from a VCA with ADSR input signal

The picture above shows the control voltage of the envelope follower following a signal of 200Hz sine wave from a VCA with a control voltage set by an ADSR.


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Calibration

None

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Special parts

None

Download

ENC Follower documentation download


ENV_Follower_PCB stuffed PCB

ENV Follower: Stuffed PCB


ENV Follower Frontview

ENV Follower: Frontview


ENV Follower: Sideview

ENV Follower: Sideview


2017 June

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