# lowpassResample

Convert signal from one sample time to another

## Description

## Examples

### Resample Discrete Sine wave

Sample a sine wave at pi samples per cycle.

t = (0:20)*2; v = sin(t);

Define the interpolation sample times.

tq = (0:400)*0.1;

Define the interpolation configuration.

config.OutputRiseFall = 2; %Fixed step sample interval config.NDelay = 5; config.SampleMode = 'fixed'; config.CausalMode = 'off';

Perform the interpolation.

[vq,vdq]=lowpassResample(t,v,tq,config);

Scatter plot the samples, plot the interpolated data, and plot the original sine wave.

scatter(t,v); hold on; plot(tq,vq); plot(tq,sin(tq)); hold off; title('Interpolated Data'); legend('samples','interpolated data','original sine wave');

Plot the interpolated derivative and the original derivative.

plot(tq,vdq); hold on; plot(tq,cos(tq)); hold off; title('Interpolated Derivative'); legend('interpolated derivative','original derivative');

## Input Arguments

`t`

— Input sample times

vector

Input sample times, specified as a fixed-step or variable-step vector.

**Data Types: **`single`

| `double`

| `int8`

| `int16`

| `int32`

| `uint8`

| `uint16`

| `uint32`

| `logical`

`v`

— Input sample values

vector

Input sample values corresponding to the input sample times defined in
`t`

, specified as a vector.

**Data Types: **`single`

| `double`

`tq`

— Output sample times

vector

Output sample times, specified as a fixed-step or variable-step vector.

**Data Types: **`single`

| `double`

`config`

— Interpolation parameters

structure

Interpolation parameters, specified as a structure with fields.

Field | Description | Value | Default |
---|---|---|---|

`OutputRiseFall` | The 0%–100% rise/fall time of the interpolated output. | Positive real scalar | `1e-10` |

`NDelay` | Number of rise/fall times by which the interpolated output will be delayed with respect to the input. | Positive real integer | `1` |

`SampleMode` | Input sampling mode, either fixed-step discrete time or variable-step discrete time. | `fixed` , `variable` | `variable` |

`CausalMode` | Determine whether you want the interpolation process to introduce delay.
Select `CausalMode` to introduce enough delay between input and
output samples in the interpolation process so that the process is strictly
causal. | `off` , `on` | `off` |

**Data Types: **`struct`

## Output Arguments

`vq`

— Interpolated samples

vector

Interpolated samples, returned as a vector.

**Data Types: **`single`

| `double`

`vdq`

— Derivative of interpolated samples

vector

Derivative of interpolated samples corresponding to `vq`

,
returned as a vector.

**Data Types: **`single`

| `double`

## More About

### Delay in Interpolated Output

You can define the number of rise/fall times by which the interpolated
output will be delayed with respect to the input using the
`config.NDelay`

parameter.

The default value of `config.NDelay`

of 1 produces an interpolation
that has no ringing due to the Gibbs phenomenon and also has modest rejected out of band
numerical artifacts.

Setting `config.NDelay`

to 5 introduces enough anti-aliasing
filtering to satisfy most applications, but introduces ringing due to the Gibbs
phenomenon.

Setting `config.NDelay`

to 10 introduces enough anti-aliasing
filtering to satisfy demanding applications, but at the cost of additional delay and
computation.

Setting `config.NDelay`

to greater than 10 is supported, but is not
required normally.

### Input Sampling Mode

You can define the input sampling mode using the
`config.SampleMode`

parameter.

The default value of `config.SampleMode`

of
`variable`

assumes that the input values are the result of a zero order
hold process. In this case, the signal value is always equal to the value of the most recent
sample. This choice is appropriate for saturated signals for which the transition times are
the most important consideration.

Setting '`config.SampleMode`

to `fixed`

assumes that
the input values are instantaneous samples of a mathematically continuous signal at
uniformly spaced sample times. Use this option for signals that are subject to a significant
amount of analog filtering.

### Causality of Interpolation Process

You can define the interpolation process as causal or not using the
`config.SampleMode`

parameter.

The default value of `config.CausalMode`

of `off`

aligns the time scale of the interpolation with the time scale of the input. This is
appropriate when all necessary input values are available in a single vector.

Setting `config.CausalMode`

to `on`

introduces
enough delay so that the sample values are available before performing an interpolation. The
interpolated sample times are therefore always delayed by a constant value with respect to
the input sample times. The required additional delay in this mode is
`config.OutputRiseFall`

times `config.NDelay`

. This
behavior mimics the behavior of the Lowpass Resampler
block.

## Extended Capabilities

### C/C++ Code Generation

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

## Version History

**Introduced in R2021a**

## See Also

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