# alignsignals

Align two signals by delaying earliest signal

## Syntax

## Description

`[`

estimates the
delay `xa`

,`ya`

]
= alignsignals(`x`

,`y`

)`D`

between the two input signals `x`

and `y`

, and returns the aligned signals `xa`

and `ya`

. The function estimates the delay using
cross-correlation.

If

`y`

is delayed with respect to`x`

, then`D`

is positive and`x`

is delayed by`D`

samples.If

`y`

is advanced with respect to`x`

, then`D`

is negative and`y`

is delayed by –`D`

samples.

The input signals need not be exact delayed copies of each other. However, the signals can be accurately aligned only if there is sufficient correlation between them. For more information on estimating covariance and correlation, see [1].

## Examples

### Align Two Signals Where First Signal Lags by Three Samples

Create two signals, `X`

and `Y`

. `X`

is exactly the same as `Y`

, except `X`

has three leading zeros and one additional following zero. Align the two signals.

X = [0 0 0 1 2 3 0 0]; Y = [1 2 3 0]; [Xa,Ya] = alignsignals(X,Y)

`Xa = `*1×8*
0 0 0 1 2 3 0 0

`Ya = `*1×7*
0 0 0 1 2 3 0

### Align Two Signals Where Second Signal Lags by Two Samples

Create two signals, `X`

and `Y`

. `Y`

is exactly the same as `X`

, except `Y`

is delayed by two samples. Align the two signals.

X = [1 2 3]; Y = [0 0 1 2 3]; [Xa,Ya,D] = alignsignals(X,Y)

`Xa = `*1×5*
0 0 1 2 3

`Ya = `*1×5*
0 0 1 2 3

D = 2

Align the signals using a maximum window size of 1.

```
maxlag = 1;
[Xa,Ya,D] = alignsignals(X,Y,Method="xcorr",MaxLag=maxlag)
```

`Xa = `*1×4*
0 1 2 3

`Ya = `*1×5*
0 0 1 2 3

D = 1

### Align Two Bilevel Waveforms Based on Rising Edges

Generate two signals that represent bilevel waveforms. The signals are sampled at 50 Hz for 20 seconds. For the first signal, the transition occurs 13 seconds after the start of the measurement. For the second signal, the transition occurs 5 seconds after the start of the measurement. The signals have different amplitudes and are embedded in white Gaussian noise of different variances. Plot the signals.

t = linspace(0,20,1001)'; e1 = 1.4*tanh(t-13)+randn(size(t))/3; e2 = tanh(3*(t-5))+randn(size(t))/5; plot(t,e1,t,e2) xlabel("Seconds") ylabel("Amplitude")

Align the signals so their transition times coincide. Correlation-based methods cannot align this type of signal adequately.

[y1,y2] = alignsignals(e1,e2); plot(y1) xlabel("Samples") ylabel("Amplitude") hold on plot(y2) hold off

Align the signals using the `risetime`

method.

[y1,y2] = alignsignals(e1,e2,Method="risetime"); plot(y1) xlabel("Samples") ylabel("Amplitude") hold on plot(y2) hold off

### Align Two Signals Using Truncate Option

Create two signals, `X`

and `Y`

. `Y`

is exactly the same as `X`

, except `Y`

has two leading zeros. Align the two signals and set the truncate option to `true`

. This option preserves the length of `X`

.

X = [1 2 3]; Y = [0 0 1 2 3]; [Xa,Ya,D] = alignsignals(X,Y,Truncate=true)

`Xa = `*1×3*
0 0 1

`Ya = `*1×5*
0 0 1 2 3

D = 2

When the truncate option truncates all the original data of `X`

, the function issues a warning.

Y = [0 0 0 0 1 2 3]; [Xa,Ya,D] = alignsignals(X,Y,Truncate=true)

Warning: All original data in the first input X has been truncated because the length of X is smaller than the estimated delay D. To avoid truncating this data do not use the "truncate" option.

`Xa = `*1×3*
0 0 0

`Ya = `*1×7*
0 0 0 0 1 2 3

D = 4

## Input Arguments

`x`

— First input signal

vector

First input signal, specified as a numeric vector of length
*L _{x}*.

**Example: **`[1 2 3]`

**Data Types: **`single`

| `double`

| `int8`

| `int16`

| `int32`

| `int64`

| `uint8`

| `uint16`

| `uint32`

| `uint64`

**Complex Number Support: **Yes

`y`

— Second input signal

vector

Second input signal, specified as a numeric vector of length
*L _{y}*.

**Example: **`[0 0 1 2 3]`

**Data Types: **`single`

| `double`

| `int8`

| `int16`

| `int32`

| `int64`

| `uint8`

| `uint16`

| `uint32`

| `uint64`

**Complex Number Support: **Yes

### Name-Value Arguments

Specify optional pairs of arguments as
`Name1=Value1,...,NameN=ValueN`

, where `Name`

is
the argument name and `Value`

is the corresponding value.
Name-value arguments must appear after other arguments, but the order of the
pairs does not matter.

**Example: **`alignsignals(X,Y,Method="npeak",PeakNum=4)`

aligns
`X`

and `Y`

based on the location of the
fourth peak in each signal.

`Method`

— Method to estimate the delay between signals

`"xcorr"`

(default) | `"maxpeak"`

| `"npeak"`

| `"risetime"`

Method to estimate the delay between signals, specified as
`"xcorr"`

, `"maxpeak"`

,
`"npeak"`

, or `"risetime"`

. You
can specify additional name-value arguments based on the specified
`Method`

.

`"xcorr"`

— Estimate the delay using cross-correlation. If you specify`Method`

as`"xcorr"`

, you can also specify`MaxLag`

.`"maxpeak"`

— Estimate the delay using the location of the highest peak in each signal. If you specify`Method`

as`"maxpeak"`

, you can optionally specify`MinPeakProminence`

and`MinPeakHeight`

.`"npeak"`

— Estimate the delay using the location of the*n*th peak in each signal. If you specify`Method`

as`"npeak"`

, you can optionally specify`PeakNum`

,`MinPeakProminence`

, and`MinPeakHeight`

.`"risetime"`

— Estimate the delay using the location of the rising edges in each signal. The function uses the specified values for`StateLevels`

to find the rising edges.

**Example: **`Method="npeak",PeakNum=3`

`MaxLag`

— Maximum window size

integer scalar

Maximum window size used to estimate the delay between signals,
specified as an integer scalar. By default, `MaxLag`

is equal to max(*L _{x}*,

*L*)–1, where

_{y}*L*is the length of

_{x}`x`

and
*L*is the length of

_{y}`y`

. If `MaxLag`

is negative,
the function uses the absolute value.This argument applies only when `Method`

is set to
`"xcorr"`

.

**Data Types: **`single`

| `double`

| `int8`

| `int16`

| `int32`

| `int64`

| `uint8`

| `uint16`

| `uint32`

| `uint64`

`PeakNum`

— Peak number

`1`

(default) | positive integer

Peak number used to align the signals, specified as a positive
integer. This argument applies only when you specify
`Method`

as `"npeak"`

.

**Data Types: **`single`

| `double`

| `int8`

| `int16`

| `int32`

| `int64`

| `uint8`

| `uint16`

| `uint32`

| `uint64`

`MinPeakProminence`

— Minimum peak prominence

`0`

(default) | real nonnegative scalar

Minimum peak prominence used to identify peaks in the signals,
specified as a real nonnegative scalar. When you specify
`MinPeakProminence`

, the function finds those
peaks that have a relative importance of at least the value specified.
For more information, see `findpeaks`

and Prominence.

This argument applies only when you specify
`Method`

as `"npeak"`

or
`"maxpeak"`

.

**Data Types: **`single`

| `double`

| `int8`

| `int16`

| `int32`

| `int64`

| `uint8`

| `uint16`

| `uint32`

| `uint64`

`MinPeakHeight`

— Minimum peak height

`–Inf`

(default) | real scalar

Minimum peak height used to identify peaks in the signals, specified
as a real scalar. When you specify `MinPeakHeight`

,
the function finds those peaks with height greater than the specified
value. For more information, see `findpeaks`

.

This argument applies only when you specify
`Method`

as `"npeak"`

or
`"maxpeak"`

.

**Data Types: **`single`

| `double`

| `int8`

| `int16`

| `int32`

| `int64`

| `uint8`

| `uint16`

| `uint32`

| `uint64`

`StateLevels`

— State levels

two-element row vector

State levels, specified as a real-valued two-element row vector. The
first element corresponds to the lower state levels of the input
signals, and the second element corresponds to the upper state levels of
the input signals. If you do not specify
`StateLevels`

, the function estimates the state
levels of the input waveform by a histogram method. For more
information, see `risetime`

.

This argument applies only when you specify
`Method`

as `"risetime"`

.

**Example: **```
Method="risetime",StateLevels=[0.5
2]
```

**Data Types: **`double`

`Truncate`

— Option to truncate the input signals

`false`

or
`0`

(default) | `true`

or `1`

Option to truncate the input signals, specified as a numeric or
logical `1`

(`true`

) or
`0`

(`false`

). When you specify
`Truncate`

as `true`

, the
lengths of `xa`

and `ya`

are equal
to the lengths of `x`

and `y`

, respectively.

If the estimated delay

`D`

is positive, the function prepends`D`

zeros to`x`

and truncates the last`D`

samples of`x`

.If

`D`

is negative, the function prepends –`D`

zeros to`y`

and truncates the last`D`

samples of`y`

.If

`D`

≥*L*, then_{x}`xa`

consists of*L*zeros and all samples of_{x}`x`

are lost. If –`D`

is ≥*L*, then_{y}`ya`

consists of*L*zeros and all samples of_{y}`y`

are lost.

## Output Arguments

`xa`

— Aligned first signal

vector

Aligned first signal, returned as a numeric vector that is aligned with
the second output argument `ya`

.

If input argument

`x`

is a row vector, then`xa`

is also a row vector.If input argument

`x`

is a column vector, then`xa`

is also a column vector.

If you specify the `Truncate`

as
`true`

and the estimated delay `D`

is positive, then `xa`

is equivalent to the input signal
`x`

with `D`

zeros prepended to it
and its last `D`

samples truncated.

`ya`

— Aligned second signal

vector

Aligned second signal, returned as a numeric vector that is aligned with
the first output argument `Xa`

.

If input argument

`y`

is a row vector, then`ya`

is also a row vector.If input argument

`y`

is a column vector, then`ya`

is also a column vector.

If you specify the `Truncate`

as
`true`

and the estimated delay `D`

is negative, then `ya`

is equivalent to the input signal
`y`

with –`D`

zeros prepended to
it and its last –`D`

samples truncated.

`D`

— Estimated delay between input signals

integer

Estimated delay between input signals, returned as an integer. This
integer represents the number of samples by which the two input signals
`x`

and `y`

are offset.

If

`y`

is delayed with respect to`x`

, then`D`

is positive and`x`

is delayed by`D`

samples.If

`y`

is advanced with respect to`x`

, then`D`

is negative and`y`

is delayed by –`D`

samples.If

`x`

and`y`

are already aligned, then`D`

is zero and neither`x`

nor`y`

are delayed.

If you specify a value for input argument `MaxLag`

,
then `D`

is less than or equal to
`MaxLag`

.

## References

[1] Orfanidis, Sophocles J. *Optimum Signal
Processing. An Introduction*. 2nd Ed. Englewood Cliffs, NJ:
Prentice-Hall, 1996.

## Extended Capabilities

### C/C++ Code Generation

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

## Version History

**Introduced in R2007a**

### R2022b: Syntaxes to be removed

These syntaxes will be removed in a future release.

Syntax | Result | Use Instead |
---|---|---|

`alignsignals(x,y,maxlag)` | Runs | `alignsignals(x,y,Method="xcorr",MaxLag=maxlag)` |

`alignsignals(x,y,maxlag,'truncate')` | Runs | `alignsignals(x,y,Method="xcorr",MaxLag=maxlag,Truncate=true)` |

### R2015b: Moved to Signal Processing Toolbox from Communications Toolbox

Previously, `alignsignals`

required Communications Toolbox™.

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