Envelope channel node

Outputs the maximum amplitude in the vicinity of each sample of the input.

The Envelope chop outputs the maximum amplitude in the vicinity of each sample of the input. It takes the absolute value of the input, and uses a sliding window of a number of samples to find the maximum amplitude near each sample.

Tip	The loudness levels of an audio track can be kept roughly constant by computing an envelope of the audio with a wide window, and then passing the original audio and the envelope to a Math chop and selecting Combine chops > Divide. This will make the amplitude approximately 1.

Parameters

Type

The two methods of calculating the envelope:

Exponential Decay

For each sample, the value is compared to the previous sample. If it is greater than the previous, the value of the envelope is equal to the value of that sample, and that sample is stored as the current peak. If it is less than, the value of the envelope decays exponentially from the last peak to the current value (as more samples pass that are smaller than the peak, the envelope decays toward the waveform). Pros of this method: envelope always encloses the data. Cons: slope can be discontinuous, making the output look bumpy.

Local Maximum Window

The channel is separated into windows of N samples determined by the Envelope Width. In each window, the maximum amplitude is found. The maximum value of the window is used as the envelope value. Pros of this method: Good shape. Cons: signal sometimes jumps outside the envelope. The signal is quantized, so pulses can be off by as much as N/2.

Envelope Bounds

Determines which values are used to compute the envelope: magnitude, power, maximum or minimum values.

Envelope Width

The width of the window to use in the envelope calculation. Adjust this width to capture as many features of the input as needed. Lower values capture more detail, while higher values create a smoother envelope. It is expressed in Units.

Interpolate

In Local Maximum window mode, this provides interpolation options for the windowed values.

Normalize Power Envelope

Keeps the total power in the signal constant when adjusting the Envelope Width.

Resample Envelope

If on, the envelope is resampled down to the rate listed in the next parameter. This is very useful for audio.

Sample Rate

The sample rate used to resample the envelope after it is calculated.

Examples

The following examples are specifically designed to demonstrate this node:

Envelope