dsp.Buffer System object

Buffer input signal

Description

The Buffer object buffers an input signal. The number of samples per channel in the input must equal the difference between the output buffer size and buffer overlap (i.e., Length - OverlapLength).

To buffer an input signal:

1. Create the dsp.Buffer object and set its properties.

2. Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects? (MATLAB).

Creation

Syntax

buff = dsp.Buffer

buff = dsp.Buffer(len,ovrlap,ics)

Description

buff = dsp.Buffer returns a buffer System object™, buff, used to buffer input signals with overlap.

buff = dsp.Buffer(len,ovrlap,ics) returns a buffer object, buff, with Length property set to len, OverlapLength property set to ovrlap, and InitialConditions property set to ics.

Properties

Unless otherwise indicated, properties are nontunable, which means you cannot change their values after calling the object. Objects lock when you call them, and the release function unlocks them.

If a property is tunable, you can change its value at any time.

For more information on changing property values, see System Design in MATLAB Using System Objects (MATLAB).

Length — Number of samples to buffer

64 (default) | positive integer

Specify the number of consecutive samples from each input channel to buffer. You can set this property to any scalar integer greater than 0.

Data Types: double | int32

OverlapLength — Amount of overlap between outputs

0 (default) | positive integer

Specify the number of samples by which consecutive output frames overlap. You can set this property to any scalar integer in the range $$0\le L<M_o$$, where M_o is the output frame size specified by the Length property.

The object takes L samples (rows) from the current output and repeats them in the next output. The object acquires $$M_o-L$$ new input samples before propagating the buffered data to the output.

Data Types: double | int32

InitialConditions — Initial output

0 (default) | scalar | vector | matrix

Specify the value of the object's initial output for cases of nonzero latency as a scalar, vector, or matrix.

When there is nonzero latency, the buffer is initialized to the value(s) specified by the InitialConditions property. The object reads from the buffer to generate the first D output samples, where

$$D=\{\begin{array}{cc}{M}_o+L& (L\ge 0)\\ M_o& (L<0)\end{array}$$

The dimensions of the InitialConditions property depend on the OverlapLength, L, and whether the input contains a single channel or multiple channels:

• When $$L\ne 0$$, the InitialConditions property must be a scalar.

• When $$L=0$$, the InitialConditions property can be a scalar, or it can be a vector with the following constraints:

  • For single-channel inputs, the InitialConditions property can be a vector of length M_o if M_i is 1, or a vector of length M_i if M_o is 1.

  • For multichannel inputs, the InitialConditions property can be a vector of length M_o * N if M_i is 1, or a vector of length M_i * N if M_o is 1.

For general buffering between arbitrary frame sizes, the InitialConditions property must be a scalar value, which is then repeated across all elements of the initial output(s). However, in the special case where the input is a 1-by-N row vector, and the output of the block is an M_o-by-N matrix, InitialConditions can be:

• An M_o-by-N matrix.

• A length-M_o vector to be repeated across all columns of the initial output(s).

• A scalar to be repeated across all elements of the initial output(s).

In the special case where the output is a 1-by-N row vector, which is the result of unbuffering an M_i-by-N matrix, the InitialConditions can be:

• A vector containing M_i samples to output sequentially for each channel during the first M_i sample times.

• A scalar to be repeated across all elements of the initial output(s).

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical

Usage

For versions earlier than R2016b, use the step function to run the System object algorithm. The arguments to step are the object you created, followed by the arguments shown in this section.

For example, y = step(obj,x) and y = obj(x) perform equivalent operations.

Syntax

y = buff(x)

Description

y = buff(x) creates output y based on current input and stored past values of x . Output length equals the Length property.

Input Arguments

x — Data input

column vector | matrix

Data input, specified as a column vector or a matrix. The number of input rows must be equal to Length – OverlapLength.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical | fi
Complex Number Support: Yes

Output Arguments

y — Buffer output

column vector | matrix

Buffer output, returned as a column vector or a matrix.

The following table shows the output dimensions of the dsp.Buffer System object when the input is a single-channel signal. M_i is the input frame size and M_o is the output frame size specified by the Length property.

Input Dimensions	Output Dimensions
1-by-1 (scalar)	Mo-by-1
Mi-by-1 (column vector)	Mo-by-1

The following table shows the output dimensions of the dsp.Buffer System object when the input is a multichannel signal. The output frame size, M_o can be greater or less than the input frame size, M_i. The object buffers each of the N input channels independently.

Input Dimensions	Output Dimensions
1-by-N (row vector)	Mo-by-N
Mi-by-N (matrix)	Mo-by-N

The data type and complexity of the output matches that of the input signal.

Data Types: single | double | int8 | int16 | int32 | int64 | uint8 | uint16 | uint32 | uint64 | logical | fi
Complex Number Support: Yes

Object Functions

To use an object function, specify the System object as the first input argument. For example, to release system resources of a System object named obj, use this syntax:

release(obj)

Common to All System Objects

step	Run System object algorithm
release	Release resources and allow changes to System object property values and input characteristics
reset	Reset internal states of System object

Examples

Create a Buffer

Note: This example runs only in R2016b or later. If you are using an earlier release, replace each call to the function with the equivalent step syntax. For example, myObject(x) becomes step(myObject,x).

Create a buffer of 256 samples with 128 sample overlap.

reader = dsp.SignalSource(randn(1024,1),128);
buff = dsp.Buffer(256,128);

for i = 1:8
    y = buff(reader());
end

y is of length 256 with 128 samples from previous input.

Algorithms

This object implements the algorithm, inputs, and outputs described on the Buffer block reference page. The object properties correspond to the block properties, except as noted.