Upsample

Resample input at higher rate by inserting zeros

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Libraries:
DSP System Toolbox / Signal Operations
DSP System Toolbox HDL Support / Signal Operations

Description

The Upsample block resamples each channel of the M_i-by-N input at a rate L times higher than the input sample rate by inserting L−1 zeros between consecutive samples. Specify the integer L in the Upsample factor, L parameter or through the input port L.

You can use this block inside triggered subsystems when you set the Rate options parameter to Enforce single-rate processing.

Examples

Upsample Signal in Single-Rate Frame-Based Processing Mode

Upsample signal in the single-rate processing mode.

• Open Script

Upsample Signal in Multirate Frame-Based Processing Mode

Upsample signal in multirate frame-based processing mode.

• Open Model

Ports

Input

in — Input signal

scalar | vector | matrix

Specify the input signal as a real or a complex-valued scalar, vector, or a matrix signal.

When you set Input processing to Columns as channels (frame based) and Rate options to Enforce single-rate processing, the input can be a variable-size signal. When the input is a variable-size signal, the frame size (number of rows) and the number of channels (columns) of the signal can change during simulation.

This port is unnamed until you set Upsample factor source to Input port. (since R2023a)

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean | fixed point
Complex Number Support: Yes

L — Upsample factor

positive integer ≤ Lmax

Since R2023a

Specify the upsample factor L as a positive integer less than or equal to the value you specify in the Maximum upsample factor, Lmax parameter.

Dependency

To enable this port, set the Upsample factor source parameter to Input port.

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

Output

Port_1 — Upsampled signal

scalar | vector | matrix

The Upsample block outputs a signal that has the same data type and complexity as the input signal. The size of the output depends on the value of the upsample factor and the option you select in the Rate options parameter.

If you set Upsample factor, L to L and Rate options to:

• Enforce single-rate processing –– The block maintains the input sample rate by increasing the output frame size by a factor of L.

• Allow multirate processing –– The block resamples the signal such that the output sample rate is L times faster than the input sample rate. The output signal has the same frame size as the input signal.

When you input the upsample factor through the input port L, the Rate options parameter is automatically set to Enforce single-rate processing. In this case, the block maintains the input sample rate at the output by increasing the output frame size by a factor of L. (since R2023a)

The output is a variable-size signal when one or both of these conditions are met:

• Input is a variable-size signal.

• Upsample factor is input through the port L.

Data Types: single | double | int8 | int16 | int32 | uint8 | uint16 | uint32 | Boolean | fixed point
Complex Number Support: Yes

Parameters

Upsample factor source — Mode of specifying upsample factor

Dialog parameter (default) | Input port

Since R2023a

Specify the upsample factor through one of these options:

• Dialog parameter –– The block enables the Upsample factor, L parameter on the block dialog box.

• Input port –– The block enables the input port L through which you can specify the upsample factor.

Upsample factor, L — Upsample factor

3 (default) | positive integer

Specify the upsample factor L by which to increase the input sample rate as a positive integer.

Dependency

To enable this parameter, set Upsample factor source to Dialog parameter. (since R2023a)

Sample offset (0 to L−1) — Sample offset

0 (default) | integer in the range [0, L−1]

Specify the sample offset D as an integer in the range [0, L−1].

Use the Sample offset (0 to L−1) parameter to delay the output samples by a specific number of sample periods. Doing so enables you to select any of the L possible output phases. The value you specify in the Sample offset (0 to L−1) parameter must be an integer in the range $$0\le D<\left(L-1\right)$$.

When you input the upsample factor through the input port L, the Sample offset (0 to L−1) parameter is not enabled in the block dialog box. In this case, the sample offset D is automatically set to 0. (since R2023a)

Dependency

To enable this parameter, set Upsample factor source to Dialog parameter. (since R2023a)

Maximum upsample factor, Lmax — Maximum upsample factor

16 (default) | positive integer ≥ 1

Since R2023a

Specify the maximum upsample factor Lmax as a positive integer greater than or equal to 1. The upsample factor you specify through the input port L must be less than or equal to Lmax.

Dependency

To enable this parameter, set Upsample factor source to Input port.

Input processing — Method to process input signals

Columns as channels (frame based) (default) | Elements as channels (sample based)

Specify how the block should process the input. You can set this parameter to one of these options:

• Columns as channels (frame based) — When you select this option, the block treats each column of the input as a separate channel. In this mode, the block can perform single-rate or multirate processing.

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

Dependency

To enable this parameter, set Upsample factor source to Dialog parameter. (since R2023a)

When you set Upsample factor source to Input port, the Input processing parameter is automatically set to Columns as channels (frame based). (since R2023a)

Rate options — Method to upsample input

Enforce single-rate processing (default) | Allow multirate processing

Specify the method that the block uses to upsample the input. You can select one of the following options:

• Enforce single-rate processing — When you select this option, the block maintains the input sample rate by increasing the output frame size by a factor of L. To select this option, you must set the Input processing parameter to Columns as channels (frame based).

• Allow multirate processing — When you select this option, the block resamples the signal such that the output sample rate is L times faster than the input sample rate.

Dependency

To enable this parameter, set Upsample factor source to Dialog parameter. (since R2023a)

When you set Upsample factor source to Input port, the Rate options parameter is automatically set to Enforce single-rate processing. (since R2023a)

Initial conditions — Initial conditions

0 (default) | scalar | vector | matrix

Specify the value with which the block is initialized for cases of nonzero latency as a scalar, vector, or a matrix. The scalar value appears in the output as the sample D+1. If this parameter is set to a vector or a matrix, the size of this parameter should be the same as that of the input. This parameter appears only when you configure the block to perform multirate processing.

Dependencies

To enable this parameter, set Rate options to Allow multirate processing.

Block Characteristics

Data Types	Boolean | double | fixed point | integer | single
Direct Feedthrough	no
Multidimensional Signals	no
Variable-Size Signals	yes
Zero-Crossing Detection	no

More About

Frame-Based Processing

When you set the Input processing parameter to Columns as channels (frame based), the block upsamples each column of the input over time. In this mode, the block can perform either single-rate or multirate processing. You can use the Rate options parameter to specify how the block upsamples the input.

• When you set the Rate options parameter to Enforce single-rate processing, the input and output of the block have the same sample rate. In this mode, the block outputs a signal with a proportionally larger frame size than the input. For upsampling by a factor of L, the output frame size is L times larger than the input frame size (M_o = M_i*L), but the input and output frame rates are equal.

  For an example of single-rate upsampling, see Upsample Signal in Single-Rate Frame-Based Processing Mode.

• When you set the Rate options parameter to Allow multirate processing, the block treats an M_i-by-N matrix input as N independent channels. The block upsamples each column of the input over time by keeping the frame size constant (M_i=M_o), and making the output frame period (T_fo) L times shorter than the input frame period (T_fo = T_fi/L).

  See the Upsample Signal in Multirate Frame-Based Processing Mode example to see the Upsample block in this mode.

Sample-Based Processing

When you set the Input processing parameter to Elements as channels (sample based), the block treats an M-by-N matrix input as M*N independent channels, and upsamples each channel over time. In this mode, the block always performs multirate processing. The output sample rate is L times higher than the input sample rate (T_so = T_si/L), and the input and output sizes are identical.

Zero Latency

The Upsample block has zero-tasking latency for all single-rate operations. The block is in a single-rate mode if you specify an upsample factor of 1 or if you set the Input processing parameter to Columns as channels (frame based) and the Rate options parameter to Enforce single-rate processing.

The Upsample block also has zero-tasking latency for multirate operations if you run your model in Simulink^® single-tasking mode.

Zero-tasking latency means that the block propagates the first input (received at t = 0) immediately after the consecutive zeros D, which you specify in the Sample offset (0 to L−1) parameter. When you input the upsample factor through the input port L, D = 0. This output (D+1) is followed in turn by the L−1 inserted zeros and the next input sample.

Nonzero Latency

The Upsample block has tasking latency for a multirate multitasking operation:

• In multirate sample-based processing mode, the initial condition for each channel appears as output sample D+1, and is followed by L−1 inserted zeros. The channel first input appears as output sample D+L+1. The Initial conditions parameter can be an M_i-by-N matrix containing one value for each channel, or a scalar value that the block applies to all signal channels.

• In multirate frame-based processing mode, the first row of the initial condition matrix appears as output sample D+1, and is followed by L−1 inserted rows of zeros, the second row of the initial condition matrix, and so on. The first row of the first input matrix appears in the output as sample M_iL+D+1. The Initial conditions parameter can be an M_i-by-N matrix, or a scalar value that the block repeats across all elements of the input matrix.

Note

For more information on latency and the Simulink tasking modes, see Excess Algorithmic Delay (Tasking Latency) and Time-Based Scheduling and Code Generation (Simulink Coder).

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

Generated code relies on the memcpy or memset function (string.h) under certain conditions.

HDL Code Generation

Generate VHDL, Verilog and SystemVerilog code for FPGA and ASIC designs using HDL Coder™.

HDL Coder™ provides additional configuration options that affect HDL implementation and synthesized logic.

Best Practices

Consider whether your model can use the Repeat block instead of the Upsample block. The Repeat block uses fewer hardware resources, so as a best practice use the Upsample block only when your algorithm requires zero-padding upsampling.

See also Multirate Model Requirements for HDL Code Generation (HDL Coder).

HDL Architecture

This block has one default HDL architecture.

HDL Block Properties

ConstrainedOutputPipeline	Number of registers to place at the outputs by moving existing delays within your design. Distributed pipelining does not redistribute these registers. The default is 0. For more details, see ConstrainedOutputPipeline (HDL Coder).
InputPipeline	Number of input pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default is 0. For more details, see InputPipeline (HDL Coder).
OutputPipeline	Number of output pipeline stages to insert in the generated code. Distributed pipelining and constrained output pipelining can move these registers. The default is 0. For more details, see OutputPipeline (HDL Coder).

Restrictions

• Input processing set to Columns as channels (frame based) is not supported.

• Upsample factor source set to Input port is not supported.

Complex Data Support

This block supports code generation for complex signals.

Version History

Introduced before R2006a

R2025a: Support for clock-rate pipelining during HDL code generation

Starting in R2025a, when you use the clock-rate pipelining optimization, the Upsample block does not act as a barrier to the optimization. As a result, clock-rate pipelining optimizes multirate designs more effectively by reducing the large amount of latency and unbalanced delays that could have previously occurred. For example, in previous releases, a multirate design with feedback loops might generate delay balancing errors when you enabled clock-rate pipelining. In R2025a, these designs do not generate delay balancing errors.

R2023a: Tune upsample factor through input port

You can now specify the upsample factor through an input port when the Upsample block operates in the single-rate frame-based processing mode. When you specify the upsample factor through the input port, you can change the factor during simulation.

R2022b: Support for variable-size input signal

Starting in R2022b, when you set Input processing to Columns as channels (frame based) and Rate options to Enforce single-rate processing, the input can be a variable-size signal. That is, the frame size (number of rows) and the number of channels (columns) of the signal can change during simulation.

When the input is a variable-size signal, the output is also a variable-size signal.