Envelope Detector

Envelope Detector

Overview

Envelope Detector takes an arbitrary audio input and returns an envelope signal calculated from that input. This is what is more commonly, albeit incorrectly, called an envelope follower; a follower is a device that uses the output of an envelope detector as a control signal, not the detector itself. An envelope detector is basically a low-order smoothing filter with adjustable RC elements for attacks and releases. Envelope Detector is capable of working with the input as peak level, mean-square, and root-mean-square, and can return the output either as a linear signal or a logarithmic one. Note that the log return is scaled from -96 dBV to 0 dBV, rather than from 0.0 V to 5.0 V, as the linear return is, and so will likely require some remapping for a specific purpose. You generally do not want to engage the optional clamping function if you're using log mode, as it will constrain the return to lie below legitimate log return values.

Most common uses of an envelope detector involve setting a threshold representing the point at which the control signal becomes active; the present module doesn't include such threshold computation because it tends to be application-specific, and any particular version that might have been included would have been too limiting.

Controls

• The Attack Knob sets the time in milliseconds it takes the detector to respond to increases in the input signal; set it low to preserve crispness and sudden attacks, and longer to smooth out sharp attacks.

• The Release Knob sets the time in milliseconds it takes the detector to respond to decreases in the input signal; generally this is most usefully set somewhat longer, so as to result in a smooth envelope, with major fluctuations averaged out.

• The Mode Toggle Button allows you to choose Peak, Mean-square (MS), or Root-mean-square (RMS) as your working representation. For all but specialized uses you'll probably get the most mileage out of Peak.

• The Scale Toggle Button selects between linear and logarithmic output (dB). Note that their ranges vary considerably, with Linear ranging over [0.0 V, 5.0V], and Log ranging over [-96 dBV, 0 dBV]. The rather extreme Log range will likely require some remapping to fit your application (there are modules available to do this sort of thing, although any module that can scale or do DC offset would suffice).

• The Clamp Toggle Button enables and disables an optional constraint of the output to an upper limit of 5.0 V. This will obviously be of more use in Linear output mode than in Log, where it will interfere with true logarithmic output.

• The Input and Output Jacks are where you input your audio signal to the unit and extract the resultant envelope signal; the related Level Adjustment Knobs let you adjust those signals from 0 - 100 %.