# Documentation

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# step

System object: comm.PhaseFrequencyOffset
Package: comm

Apply phase and frequency offsets to input signal

## Syntax

```Y = step(H,X) Y = step(H,X,FRQ) ```

## Description

### Note

Starting in R2016b, instead of using the `step` method to perform the operation defined by the System object™, you can call the object with arguments, as if it were a function. For example, `y = step(obj,x)` and `y = obj(x)` perform equivalent operations.

`Y = step(H,X)` applies phase and frequency offsets to input `X`, and returns `Y`. The input `X` is a double or single precision matrix `X`, of dimensions MxN. M is the number of time samples in the input signals and N is number of channels. Both M and N can be equal to 1. The object adds phase and frequency offsets independently to each column of `X`. The data type and dimensions of `X` and `Y` are the same.

`Y = step(H,X,FRQ)` uses `FRQ` as the frequency offset that the object applies to input `X` when you set the `FrequencyOffsetSource` property to 'Input port'. When the `X` input is an MxN matrix, the value for `FRQ` can be a numeric scalar, an Mx1 or 1xN numeric vector, or an MxN numeric matrix. When the `FRQ` input is a scalar, the object applies a constant frequency offset, `FRQ`, to each column of `X`. When the `FRQ` input is an Mx1 vector, the object applies time varying frequency offsets, which are specified in the `FRQ` vector, to each column of `X`. When the `FRQ` input is a 1xN vector, the object applies the ith constant frequency offset in `FRQ` to the ith column of `X`. When the `FRQ` input is an MxN matrix, the object applies the ith time varying frequency offsets, specified in the ith column of `FRQ`, to the ith column of `X`.

### Note

`obj` specifies the System object on which to run this `step` method.

The object performs an initialization the first time the `step` method is executed. This initialization locks nontunable properties (MATLAB) and input specifications, such as dimensions, complexity, and data type of the input data. If you change a nontunable property or an input specification, the System object issues an error. To change nontunable properties or inputs, you must first call the `release` method to unlock the object.