DSP Blockset

Delay Line

Rebuffer a sequence of inputs with a one-sample shift.

Library

Signal Management / Buffers

Description

The Delay Line block buffers the input samples into a sequence of overlapping or underlapping matrix outputs. In the most typical use (sample-based inputs), each output differs from the preceding output by only one sample, as illustrated below for scalar input.

Note that the first output of the block in the example above is all zeros; this is because the Initial Conditions parameter is set to zero. Due to the latency of the Delay Line block, all outputs are delayed by one frame, the entries of which are defined by the Initial Conditions parameter.

Sample-Based Operation

In sample-based operation, the Delay Line block buffers a sequence of sample-based length-N vector inputs (1-D, row, or column) into a sequence of overlapping frame-based M_o-by-N matrix outputs, where M_o is specified by the Delay line size parameter (M_o>1). That is, each input vector becomes a row in the frame-based output matrix.

At each sample time the new input vector is added in the last row of the output, so each output overlaps the previous output by M_o-1 samples. Therefore, the output sample period and frame period is the same as the input sample period (T_so=T_si, and T_fo=T_si). When M_o=1, the input is simply passed through to the output and retains the same dimension, but becomes frame-based. The latency of the block always causes an initial delay in the output; the value of the first output is specified by the Initial conditions parameter (see Initial Conditions below). Sample-based full-dimension matrix inputs are not accepted.

The Delay Line block's sample-based operation is similar to that of a Buffer block with Buffer size equal to M_o and Buffer overlap equal to M_o-1, except that the Buffer block has a different latency.

In the model below, the block operates on a sample-based input with a Delay line size of 3.

The input vectors in the example above do not begin appearing at the output until the second row of the second matrix due to the block's latency (see Initial Conditions below). The first output matrix (all zeros in this example) reflects the block's Initial conditions setting. As for any sample-based input, the output frame rate and output sample rate are both equal to the input sample rate.

Frame-Based Operation

In frame-based operation, the Delay Line block rebuffers a sequence of frame-based M_i-by-N matrix inputs into a sequence of frame-based M_o-by-N matrix outputs, where M_o is the output frame size specified by the Delay line size parameter. Depending on whether M_o is greater than, less than, or equal to the input frame size, M_i, the output frames can be underlapped or overlapped. Each of the N input channels is rebuffered independently.

When M_o > M_i, the output frame overlap is the difference between the output and input frame size, M_o-M_i. When M_o < M_i, the output is underlapped; the Delay Line block discards the first M_i-M_o samples of each input frame so that only the last M_o samples are buffered into the corresponding output frame. When M_o = M_i, the output data is identical to the input data, but is delayed by the latency of the block. Due to the block's latency, the outputs are always delayed by one frame, the entries of which are specified by the Initial conditions (see Initial Conditions below).

The output frame period is equal to the input frame period (T_fo=T_fi). The output sample period, T_so, is therefore equal to T_fi/M_o, or equivalently, T_si(M_i/M_o)

In the model below, the block rebuffers a two-channel frame-based input with a Delay line size of 3.

The first output frame in the example is a product of the latency of the Delay Line block; it is all zeros because the Initial conditions is set to be zero. Since the input frame size, 4, is larger than the output frame size, 3, only the last three samples in each input frame are propagated to the corresponding output frame. The frame periods of the input and output are the same, and the output sample period is T_si(M_i/M_o), or 4/3 the input sample period.

Initial Conditions

The Delay Line block's buffer is initialized to the value specified by the Initial condition parameter. The block outputs this buffer at the first simulation step (t=0). If the block's output is a vector, the Initial condition can be a vector of the same size, or a scalar value to be repeated across all elements of the initial output. If the block's output is a matrix, the Initial condition can be a matrix of the same size, a vector (of length equal to the number of matrix rows) to be repeated across all columns of the initial output, or a scalar to be repeated across all elements of the initial output.

Dialog Box

Delay line size

The number of rows in output matrix, M_o.

Initial conditions

The value of the block's initial output, a scalar, vector, or matrix.

Supported Data Types

• Double-precision floating point
• Single-precision floating point
• Fixed-point
• Custom data types
• Boolean
• 8-, 16-, and 32-bit signed integers
• 8-, 16-, and 32-bit unsigned integers

To learn how to convert to the above data types in MATLAB and Simulink, see Supported Data Types and How to Convert to Them.

See Also

Buffer	DSP Blockset
Triggered Delay Line	DSP Blockset

See Buffering Sample-Based and Frame-Based Signals for related information. Also see Buffers for a list of all the blocks in the Buffers library.

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