Documentation Center

  • Trial Software
  • Product Updates

Derepeat

Reduce sampling rate by averaging consecutive samples

Library

Sequence Operations

Description

The Derepeat block resamples the discrete input at a rate 1/N times the input sample rate by averaging N consecutive samples. This is one possible inverse of the DSP System Toolbox™ Repeat block. The positive integer N is the Derepeat factor parameter in the Derepeat dialog.

The Initial condition parameter prescribes elements of the output when it is still too early for the input data to show up in the output. If the dimensions of the Initial condition parameter match the output dimensions, then the parameter represents the initial output value. If Initial condition is a scalar, then it represents the initial value of each element in the output. The block does not support empty matrices for initial conditions.

The input can have any shape or frame status. The block accepts the data types single and double. The output signal inherits its data type from the input signal.

This block works within a triggered subsystem, as long as you use it in the single-rate mode.

Single-Rate Processing

The block derepeats each frame, treating distinct channels independently. Each element of the output is the average of N consecutive elements along a column of the input matrix. The Derepeat factor must be less than the frame size.

When you set the Rate options parameter to Enforce single-rate processing, the input and output of the block have the same sample rate. The block reduces the sampling rate by using a proportionally smaller frame size than the input. Derepeat factor should be an integer factor of the number of rows in the input vector or matrix. For derepetition by a factor of N, the output frame size is 1/N times the input frame size, but the input and output frame rates are equal. When you use this option, the Initial condition parameter does not apply and the block incurs no delay, because the input data immediately shows up in the output.

For example, if a single-channel input with 64 elements is derepeated by a factor of 4, then the output contains 16 elements. The input and output frame periods are equal.

Multirate Processing

When you set the Rate options parameter to Allow multirate processing, the input and output of the Derepeat block are the same size, but the sample rate of the output is N times slower than that of the input. When the block is in multirate processing mode, you must also specify a value for the Input processing parameter:

  • When you set the Input processing parameter to Elements as channels (sample based), then the block assumes that the input is a vector or matrix whose elements represent samples from independent channels. The block averages samples from each channel independently over time. The output period is N times the input period, and the input and output sizes are identical. The output is delayed by one output period, and the first output value is the Initial condition value. If you set Rate options to Enforce single-rate processing, the block will generate an error message.

  • When you set the Input processing parameter to Columns as channels (frame based), The block reduces the sampling rate by using a proportionally longer frame period at the output port than at the input port. For derepetition by a factor of N, the output frame period is N times the input frame period, but the input and output frame sizes are equal. The output is delayed by one output frame, and the first output frame is determined only by the Initial condition value. The block derepeats each frame, treating distinct channels independently. Each element of the output is the average of N consecutive elements along a column of the input matrix. The Derepeat factor must be less than the frame size.

    For example, if a single-channel input with a frame period of 1 second is derepeated by a factor of 4, then the output has a frame period of 4 seconds. The input and output frame sizes are equal.

Dialog Box

Derepeat factor, N

The number of consecutive input samples to average in order to produce each output sample.

Input processing

Specify how the block processes the input signal. You can set this parameter to one of the following options:

  • Columns as channels (frame based) — When you select this option, the block treats each column of the input as a separate channel.

  • Elements as channels (sample based) — When you select this option, the block treats each element of the input as a separate channel.

    Note:   The Inherited (this choice will be removed - see release notes) option will be removed in a future release. See Frame-Based Processing in the Communications System Toolbox™ Release Notes for more information.

Rate options

Select the rate processing option for the block.

  • Enforce single-rate processing — When you select this option, the input and output signals have the same port sample time. The block implements the rate change by making a size change at the output when compared to the input. The output width equals the product of the number of symbols and the Samples per symbol parameter value.

  • Allow multirate processing — When you select this option, the input and output signals have different port sample times. The output sample time equals the symbol period divided by the Samples per symbol parameter value.

      Note:   The option Inherit from input (this choice will be removed - see release notes) will be removed in a future release. See Frame-Based Processing in the Communications System Toolbox Release Notes for more information.

Initial condition

The value with which to initialize the block.

See Also

Repeat (DSP System Toolbox documentation), Downsample (DSP System Toolbox documentation)

Was this topic helpful?