envelope — Compute upper and lower signal envelopes.
envelope(x) returns upper and lower envelopes for a finite real signal vector or for each column of a finite real matrix. The default analytic mode removes each channel mean, computes the magnitude of the analytic signal, and adds the mean back to the upper and lower bounds.
Syntax
yupper = envelope(x)
[yupper, ylower] = envelope(x)
yupper = envelope(x, n, method)
[yupper, ylower] = envelope(x, n, method)Inputs
| Name | Type | Required | Default | Description |
|---|---|---|---|---|
x | NumericArray | Yes | — | Finite real-valued signal vector or matrix, processed column-wise. |
n | NumericScalar | Yes | — | Filter/window length for analytic or RMS mode, or peak separation for peak mode. |
method | StringScalar | No | "analytic" | Envelope method: `analytic`, `rms`, or `peak`. |
Returns
| Name | Type | Description |
|---|---|---|
yupper | NumericArray | Upper signal envelope. |
ylower | NumericArray | Lower signal envelope. |
Returned values from envelope depend on how many outputs the caller requests.
Errors
| Identifier | When | Message |
|---|---|---|
RunMat:envelope:ArgCount | The argument count is outside supported forms. | envelope: expected envelope(x), envelope(x, n), or envelope(x, n, method) |
RunMat:envelope:InvalidSignal | Input is not a finite real numeric vector or matrix. | envelope: x must be a finite real numeric vector or matrix |
RunMat:envelope:InvalidLength | Filter/window length or peak separation is not a positive integer. | envelope: n must be a positive integer scalar |
RunMat:envelope:InvalidMethod | Method is not analytic, rms, or peak. | envelope: method must be 'analytic', 'rms', or 'peak' |
RunMat:envelope:Internal | Envelope computation or output tensor assembly fails internally. | envelope: internal error |
RunMat:envelope:TooManyOutputs | More than two output arguments are requested. | envelope: expected at most two output arguments |
How envelope works
yupper = envelope(x)returns the upper envelope.[yupper, ylower] = envelope(x)returns both bounds.envelope(x, n)uses analytic mode and computes the analytic signal with a Kaiser-windowed Hilbert FIR filter of lengthn.envelope(x, n, 'analytic')explicitly selects the same Hilbert FIR-filter path.envelope(x, wl, 'rms')computes a centered sliding RMS envelope over a window ofwlsamples.envelope(x, np, 'peak')detects local maxima/minima separated by at leastnpsamples and interpolates them with a spline curve.- Statement form with no outputs plots the signal with the upper and lower envelopes.
- MATLAB-compatible mode accepts single- and double-precision signal data and controls. Typed-integer signal data or length controls are explicit RunMat extensions; integer data crosses into the floating envelope computation only after exact storage is read.
- The public source does not state the output class for single-precision host input, so that compatibility detail remains evidence-open. RunMat preserves single-precision output for single-precision input consistently across host and resident execution.
Examples
Analytic envelope of an amplitude-modulated tone
t = (0:127) / 128;
x = (1.25 + 0.5*sin(2*pi*t)) .* sin(2*pi*8*t);
[up, lo] = envelope(x);Centered moving RMS envelope
x = [0 3 4 0];
[up, lo] = envelope(x, 3, 'rms');Peak envelope
x = [0 2 0 -1 0 3 0];
[up, lo] = envelope(x, 2, 'peak');Column-wise matrix envelopes
x = [sin(0:0.1:10)' cos(0:0.1:10)'];
[up, lo] = envelope(x);Using envelope with coding agents
Open a RunMat example with live inputs, then ask the agent to explain how envelope changes the result.
Run a small envelope example, explain the result, then change one input and compare the output.
FAQ
What is the default envelope method?⌄
The default is analytic-envelope mode using the magnitude of the analytic signal.
How are matrix inputs handled?⌄
envelope processes each matrix column independently and returns outputs with the same shape as the input.
Does envelope plot when no outputs are requested?⌄
Yes. Statement form renders the signal, upper envelope, and lower envelope using the line-plot pipeline.
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Open-source implementation
Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how envelope is executed, line by line, in Rust.
- View the source for envelope in Rust on GitHub
- Learn how the RunMat runtime works
- Found a bug? Open an issue with a minimal reproduction.
About RunMat
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