upsample

R2026b

Increase sample rate by integer factor

Syntax

y = upsample(x,n)

y = upsample(x,n,phase)

Description

y = upsample(x,n) increases the sample rate of x by inserting n – 1 zeros between samples. If x is a matrix, the function treats each column as a separate sequence.

y = upsample(x,n,phase) specifies the number of samples by which to offset the upsampled sequence.

Examples

Increase Sample Rates

Increase the sample rate of a sequence by a factor of 3.

x = [1 2 3 4];
y = upsample(x,3)

y = 1×12

     1     0     0     2     0     0     3     0     0     4     0     0

Increase the sample rate of the sequence by a factor of 3 and add a phase offset of 2.

x = [1 2 3 4];
y = upsample(x,3,2)

y = 1×12

     0     0     1     0     0     2     0     0     3     0     0     4

Increase the sample rate of a matrix by a factor of 3.

x = [1 2;
     3 4;
     5 6];
y = upsample(x,3)

y = 9×2

     1     2
     0     0
     0     0
     3     4
     0     0
     0     0
     5     6
     0     0
     0     0

Upsample Sine Waveform

Since R2026b

Generate a 101-second sine waveform with a fundamental frequency of 0.01 Hz and a space of 5 seconds between consecutive samples.

ts = 5;
tx = (1:ts:101)';
x = sin(2*pi*0.01*tx);

Upsample the signal using an upsampling factor of 3. Compare the original and upsampled signals. To produce the upsampled signal, the upsample function inserts two zeros between sine samples.

n = 3;
ty = (1:ts/n:ts*numel(x))';
y = upsample(x,n);
plot(tx,x,"o",ty,y,".")
legend(["Original" "Upsampled"])

Upsample the signal using an upsampling factor of 3 and a phase offset of 1. Compare the original and upsampled signals. Because of the specified phase offset, the first sample of the original signal matches with the second sample on the upsampled signal.

p = 1;
ty = (1:ts/n:ts*numel(x))';
y = upsample(x,n,p);
plot(ts/n*p+tx,x,"o",ty,y,".")
legend(["Original" "Upsampled"])

Input Arguments

x — Input array

vector | matrix

Input array, specified as a vector or matrix. If x is a matrix, the function treats the columns as independent channels.

Example: cos(pi/4*(0:159)) + randn(1,160) specifies a sinusoid embedded in white Gaussian noise.

Example: cos(pi./[4;2]*(0:159))' + randn(160,2) specifies a two-channel noisy sinusoid.

n — Upsampling factor

positive integer

Upsampling factor, specified as a positive integer.

Data Types: single | double

phase — Offset

0 (default) | positive integer

Offset, specified as a positive integer from 0 to n – 1.

Data Types: single | double

Output Arguments

y — Upsampled array

vector | matrix

Upsampled array, returned as a vector or matrix. y has x × n samples.

Tip

To remove the imaging artifacts from the upsampled output y, apply a lowpass filter to y with cutoff normalized frequency of pi/n rad/sample. Alternatively, use the interp function.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

GPU Code Generation
Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

Thread-Based Environment

Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

The upsample function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

GPU Arrays

Accelerate code by running on a graphics processing unit (GPU) using Parallel Computing Toolbox™.

This function fully supports GPU arrays. For more information, see Run MATLAB Functions on a GPU (Parallel Computing Toolbox).

Version History

Introduced before R2006a

R2026b: Use thread-based environments

You can use upsample in thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

R2024a: upsample supports GPU code generation

The upsample function supports code generation for graphical processing units (GPUs). You must have MATLAB^® Coder™ and GPU Coder™ to generate CUDA^® code.