# dsp.SineWave

Generate discrete sine wave

## Description

The `dsp.SineWave`

System object™ generates a real or complex, multichannel sinusoidal signal with independent
amplitude, frequency, and phase in each output channel.

For both real and complex sinusoids, the Amplitude,
Frequency, and PhaseOffset properties can be scalars or length-*N* vectors, where
*N* is the number of channels in the output. When you specify at least one
of these properties as a length-*N* vector, scalar values specified for the
other properties are applied to each of the *N* channels.

To generate a discrete-time sinusoidal signal:

Create the

`dsp.SineWave`

object and set its properties.Call the object with arguments, as if it were a function.

To learn more about how System objects work, see What Are System Objects?

## Creation

### Syntax

### Description

creates a sine wave
object that generates a real-valued sinusoid with an amplitude of 1, a frequency of 100
Hz, and a phase offset of 0. By default, the sine wave object generates only one
sample.`sine`

= dsp.SineWave

creates a sine wave object with each specified property set to the specified value.
Enclose each property name in single quotes. `sine`

= dsp.SineWave(`Name,Value`

)

**Example: **sine = dsp.SineWave('Amplitude',2);

creates a sine wave object with the Amplitude property set to `sine`

= dsp.SineWave(amp,freq,phase,`Name,Value`

)`amp`

, Frequency property set to `freq`

,
PhaseOffset property set to `phase`

,
and anyother specified properties set to the specified values.

## Properties

Unless otherwise indicated, properties are *nontunable*, which means you cannot change their
values after calling the object. Objects lock when you call them, and the
`release`

function unlocks them.

If a property is *tunable*, you can change its value at
any time.

For more information on changing property values, see System Design in MATLAB Using System Objects.

`Amplitude`

— Amplitude of sine wave

`1`

(default) | scalar | vector

Amplitude of the sine wave, specified as one of the following:

scalar –– A scalar applies to all channels.

vector –– A length-

*N*vector contains the amplitudes of the sine waves in each of the*N*output channels. The vector length must be the same as that specified for the Frequency and PhaseOffset properties.

**Tunable: **Yes

#### Dependencies

This property is tunable only when you set Method to either ```
'Trigonometric
function'
```

or `'Differential'`

.

**Data Types: **`single`

| `double`

| `int8`

| `int16`

| `int32`

| `int64`

| `uint8`

| `uint16`

| `uint32`

| `uint64`

`Frequency`

— Frequency of sine wave

`100`

(default) | scalar | vector

Frequency of the sine wave in Hz, specified as one of the following:

scalar –– A scalar applies to all channels.

vector –– A length-

*N*vector contains the frequencies of the sine waves in each of the*N*output channels. The vector length must be the same as that specified for the Amplitude and PhaseOffset properties.

**Data Types: **`single`

| `double`

| `int8`

| `int16`

| `int32`

| `int64`

| `uint8`

| `uint16`

| `uint32`

| `uint64`

`PhaseOffset`

— Phase offset of sine wave

`0`

(default) | scalar | vector

Phase offset of the sine wave in radians, specified as one of the following:

**Data Types: **`single`

| `double`

| `int8`

| `int16`

| `int32`

| `int64`

| `uint8`

| `uint16`

| `uint32`

| `uint64`

`ComplexOutput`

— Flag that indicates whether waveform is real or complex

`false`

(default) | `true`

Flag that indicates whether the waveform is real or complex, specified as either:

`false`

–– The waveform output is real.`true`

–– The waveform output is complex.

`Method`

— Method used to generate sinusoids

`'Trigonometric function'`

(default) | `'Table lookup'`

| `'Differential'`

Method used to generate sinusoids, specified as one of the following:

`'Trigonometric function'`

–– The object computes the sinusoid by sampling the continuous-time function.`'Table lookup'`

–– The object precomputes the unique samples of every output sinusoid at the start of the simulation, and recalls the samples from memory as needed.`'Differential'`

–– The object uses an incremental algorithm. This algorithm computes the output samples based on the output values computed at the previous sample time and precomputed update terms.

`TableOptimization`

— Optimize table of sine values for speed or memory

`'Speed'`

(default) | `'Memory'`

Optimize table of sine values for speed or memory, specified as either:

`'Speed'`

–– The table contains*k*elements, where*k*is the number of input samples in one full period of the sine wave. The period of each sinusoid must be an integer multiple of 1/*Fs*, where*Fs*is the value of the SampleRate property value. That is, each element of the Frequency property must be of the form*Fs*/*m*, where*m*is an integer greater than`1`

.`'Memory'`

–– The table contains*k*/4 elements.

#### Dependencies

This property applies only when you set the `Method`

property
to `'Table lookup'`

.

`SampleRate`

— Sample rate of output signal

`1000`

(default) | positive scalar

Sample rate of output signal in Hz, specified as a positive scalar.

**Example: **`44100`

**Example: **`22050`

`SamplesPerFrame`

— Number of samples per frame

`1`

(default) | positive integer

Number of consecutive samples from each sinusoid to buffer into the output frame, specified as a positive integer.

**Example: **`1000`

**Example: **`5000`

**Data Types: **`single`

| `double`

| `int8`

| `int16`

| `int32`

| `int64`

| `uint8`

| `uint16`

| `uint32`

| `uint64`

`OutputDataType`

— Data type of the sine wave output

`'double'`

(default) | `'single'`

| `'Custom'`

Data type of the sine wave output, specified as `'double'`

,
`'single'`

, or `'Custom'`

.

**Fixed-Point Properties**

`CustomOutputDataType`

— Output word and fraction lengths

`numerictype([],16)`

(default) | `numerictype([],32,30)`

Output word and fraction lengths, specified as an autosigned numeric type with a word length of 16.

**Example: **numerictype([],32,30)

**Example: **numerictype([],16,15)

#### Dependencies

This property applies only when you set the Method property to ```
'Table
lookup'
```

and the OutputDataType property to
`'Custom'`

.

## Usage

### Syntax

### Output Arguments

`sineOut`

— Sine wave output

vector | matrix

Sine wave output, returned as a vector or matrix. The SamplesPerFrame property determines the number of
rows in the output matrix. If the Frequency or the PhaseOffset property is a vector, the length of the
vector determines the number of columns (channels) in the output matrix. If the
`Frequency`

or the `PhaseOffset`

properties is
a scalar, then the number of channels in the output matrix is 1.

The OutputDataType property sets the data type of the output.

**Data Types: **`single`

| `double`

| `fi`

## Object Functions

To use an object function, specify the
System object as the first input argument. For
example, to release system resources of a System object named `obj`

, use
this syntax:

release(obj)

## Examples

### Generate a Sine Wave Signal

Generate a sine wave with an amplitude of 2, frequency of 10 Hz, and an initial phase of 0.

sine1 = dsp.SineWave(2,10); sine1.SamplesPerFrame = 1000; y = sine1(); plot(y)

Generate two sine waves offset by a phase of pi/2 radians.

sine2 = dsp.SineWave; sine2.Frequency = 10; sine2.PhaseOffset = [0 pi/2]; sine2.SamplesPerFrame = 1000; y = sine2(); plot(y)

### Filter Frames of a Noisy Sine Wave Signal in MATLAB

This example shows how to lowpass filter a noisy signal in MATLAB® and visualize the original and filtered signals using a spectrum analyzer. For a Simulink® version of this example, see Filter Frames of a Noisy Sine Wave Signal in Simulink.

**Specify Signal Source**

The input signal is the sum of two sine waves with frequencies of 1 kHz and 10 kHz. The sampling frequency is 44.1 kHz.

Sine1 = dsp.SineWave('Frequency',1e3,'SampleRate',44.1e3); Sine2 = dsp.SineWave('Frequency',10e3,'SampleRate',44.1e3);

**Create Lowpass Filter**

The lowpass FIR filter, `dsp.LowpassFilter`

, designs a minimum-order FIR lowpass filter using the generalized Remez FIR filter design algorithm. Set the passband frequency to 5000 Hz and the stopband frequency to 8000 Hz. The passband ripple is 0.1 dB and the stopband attenuation is 80 dB.

FIRLowPass = dsp.LowpassFilter('PassbandFrequency',5000,... 'StopbandFrequency',8000);

**Create Spectrum Analyzer**

Set up the spectrum analyzer to compare the power spectra of the original and filtered signals. The spectrum units are dBm.

SpecAna = spectrumAnalyzer('PlotAsTwoSidedSpectrum',false,... 'SampleRate',Sine1.SampleRate,... 'ShowLegend',true, ... 'YLimits',[-145,45]); SpecAna.ChannelNames = {'Original noisy signal',... 'Lowpass filtered signal'};

**Specify Samples per Frame**

This example uses frame-based processing, where data is processed one frame at a time. Each frame of data contains sequential samples from an independent channel. Frame-based processing is advantageous for many signal processing applications because you can process multiple samples at once. By buffering your data into frames and processing multisample frames of data, you can improve the computational time of your signal processing algorithms. Set the number of samples per frame to 4000.

Sine1.SamplesPerFrame = 4000; Sine2.SamplesPerFrame = 4000;

**Filter the Noisy Sine Wave Signal**

Add zero-mean white Gaussian noise with a standard deviation of 0.1 to the sum of sine waves. Filter the result using the FIR filter. While running the simulation, the spectrum analyzer shows that frequencies above 8000 Hz in the source signal are attenuated. The resulting signal maintains the peak at 1 kHz because it falls in the passband of the lowpass filter.

for i = 1 : 1000 x = Sine1()+Sine2()+0.1.*randn(Sine1.SamplesPerFrame,1); y = FIRLowPass(x); SpecAna(x,y); end release(SpecAna)

### Bandpass Filtering of Sinusoids

Bandpass filter a discrete-time sine wave signal which consists of three sinusoids at frequencies, 1 kHz, 10 kHz, and 15 kHz.

Design an FIR Equiripple bandpass filter by first creating a bandpass filter design specifications object, and then designing a filter using these specifications.

**Design Bandpass Filter**

Create a bandpass filter design specifications object using `fdesign.bandpass`

.

bandpassSpecs = fdesign.bandpass('Fst1,Fp1,Fp2,Fst2,Ast1,Ap,Ast2', ... 1/4,3/8,5/8,6/8,60,1,60);

List the available design methods for this object.

designmethods(bandpassSpecs)

Design Methods for class fdesign.bandpass (Fst1,Fp1,Fp2,Fst2,Ast1,Ap,Ast2): butter cheby1 cheby2 ellip equiripple kaiserwin

To design an Equiripple filter, pick `'equiripple'`

.

`bpFilter = design(bandpassSpecs,'equiripple',Systemobject=true)`

bpFilter = dsp.FIRFilter with properties: Structure: 'Direct form' NumeratorSource: 'Property' Numerator: [-0.0043 -3.0812e-15 0.0136 3.7820e-15 -0.0180 -4.2321e-15 7.1634e-04 4.0993e-15 0.0373 -4.1057e-15 -0.0579 3.7505e-15 0.0078 -3.4246e-15 0.1244 2.4753e-15 -0.2737 -8.6287e-16 0.3396 -8.6287e-16 -0.2737 ... ] (1x37 double) InitialConditions: 0 Use get to show all properties

Visualize the frequency response of the designed filter.

freqz(bpFilter,[],44100)

**Create Sinusoidal Signal**

Create a signal that is a sum of three sinusoids with frequencies at 1 kHz, 10 kHz, and 15 kHz. Initialize spectrum analyzer to view the original signal and the filtered signal.

Sine1 = dsp.SineWave(Frequency=1e3,SampleRate=44.1e3,SamplesPerFrame=4000); Sine2 = dsp.SineWave(Frequency=10e3,SampleRate=44.1e3,SamplesPerFrame=4000); Sine3 = dsp.SineWave(Frequency=15e3,SampleRate=44.1e3,SamplesPerFrame=4000); SpecAna = spectrumAnalyzer(PlotAsTwoSidedSpectrum=false, ... SampleRate=Sine1.SampleRate, ... ShowLegend=true, ... YLimits=[-240,45]); SpecAna.ChannelNames = {'Original noisy signal','Bandpass filtered signal'};

**Filter Sinusoidal Signal**

Filter the sinusoidal signal using the bandpass filter that has been designed. View the original signal and the filtered signal in the spectrum analyzer. The tone at 1 kHz is filtered out and attenuated. The tone at 10 kHz is unaffected, and the tone at 15 kHz is mildly attenuated because it appears in the transition band of the filter.

for i = 1:5000 x = Sine1()+Sine2()+Sine3(); y = bpFilter(x); SpecAna(x,y); end release(SpecAna)

## More About

### Sinusoid

A real-valued, discrete-time sinusoid is defined as:

$$y(n)=A\mathrm{sin}(2\pi fn+\varphi )$$

where *A* is the amplitude, *f* is the
frequency in Hz, and φ is the initial phase, or phase offset, in radians.

A complex sinusoid is defined as:

$$y(n)=A{e}^{j(2\pi fn+\varphi )}$$

## Algorithms

### Trigonometric Function

The trigonometric function method computes the sinusoid in the *i*th
channel, *y*_{i}, by sampling the continuous
function

$$\begin{array}{ll}{y}_{i}={A}_{i}\mathrm{sin}\left(2\pi {f}_{i}t+{\varphi}_{i}\right)\hfill & \text{(real)}\hfill \\ \begin{array}{l}\\ \text{or}\\ \end{array}\hfill & \hfill \\ {y}_{i}={A}_{i}{e}^{j\left(2\pi {f}_{i}t+{\varphi}_{i}\right)}\hfill & \text{(complex)}\hfill \end{array}$$

with a period of *T _{s}*, where you specify

*T*in the sample time.

_{s}At each sample time, the algorithm evaluates the sine function at the appropriate time
value *within the first cycle* of the sinusoid. By constraining
trigonometric evaluations to the first cycle of each sinusoid, the algorithm avoids the
imprecision of computing the sine of very large numbers. This constraint also eliminates the
possibility of discontinuity during extended operations, when an absolute time variable
might overflow. This method therefore avoids the memory demands of the table lookup method
at the expense of many more floating-point operations.

### Table Lookup

The table lookup method precomputes the *unique* samples of every
output sinusoid at the start of the simulation, and recalls the samples from memory as
needed. Because a table of finite length can only be constructed when all output sequences
repeat, the method requires that the period of every sinusoid in the output be evenly
divisible by the sample period. That is,
1/(*f _{i}T_{s}*) =

*k*must be an integer value for every channel

_{i}*i*= 1, 2, ...,

*N*.

When the algorithm optimizes the table of sine values for `Speed`

, the
table constructed for each channel contains *k _{i}*
elements. When the optimization is for

`Memory`

, the table constructed for
each channel contains *k*/4 elements.

_{i}For long output sequences, the table lookup method requires far fewer floating-point operations than any of the other methods. However, the method can demand considerably more memory, especially for high sample rates (long tables). This method is recommended for models that are intended to emulate or generate code for DSP hardware, which need to be optimized for execution speed.

**Note**

The lookup table for this object is constructed from double-precision floating-point
values. When you use the `Table Lookup`

computation mode, the maximum
amount of precision you can achieve in your output is 53 bits. Setting the word length of
the output data type to values greater than 53 bits does not improve the precision of your
output.

### Differential

The differential method uses an incremental algorithm. This algorithm computes the output samples based on the output values computed at the previous sample time (and precomputed update terms) by making use of the following identities.

$$\begin{array}{l}\mathrm{sin}\left(t+{T}_{s}\right)=\mathrm{sin}\left(t\right)\mathrm{cos}\left({T}_{s}\right)+\mathrm{cos}\left(t\right)\mathrm{sin}\left({T}_{s}\right)\\ \mathrm{cos}\left(t+{T}_{s}\right)=\mathrm{cos}\left(t\right)\mathrm{cos}\left({T}_{s}\right)-\mathrm{sin}\left(t\right)\mathrm{sin}\left({T}_{s}\right)\end{array}$$

The update equations for the sinusoid in the *i*th channel,
*y _{i}*, can therefore be written in matrix form
as

$$\left[\begin{array}{c}\mathrm{sin}\left\{2\pi {f}_{i}\left(t+{T}_{s}\right)+{\varphi}_{i}\right\}\\ \mathrm{cos}\left\{2\pi {f}_{i}\left(t+{T}_{s}\right)+{\varphi}_{i}\right\}\end{array}\right]=\left[\begin{array}{cc}\mathrm{cos}\left(2\pi {f}_{i}{T}_{s}\right)& \mathrm{sin}\left(2\pi {f}_{i}{T}_{s}\right)\\ -\mathrm{sin}\left(2\pi {f}_{i}{T}_{s}\right)& \mathrm{cos}\left(2\pi {f}_{i}{T}_{s}\right)\end{array}\right]\left[\begin{array}{c}\mathrm{sin}\left(2\pi {f}_{i}t+{\varphi}_{i}\right)\\ \mathrm{cos}\left(2\pi {f}_{i}t+{\varphi}_{i}\right)\end{array}\right]$$

where you specify *T _{s}* in the sample time.
Since

*T*is constant, the right-hand matrix is a constant and can be computed once at the start of the simulation. The value of

_{s}*A*sin[2π

_{i}*f*(

_{i}*t*+

*T*)+

_{s}*ϕ*] is then computed from the values of sin(2π

_{i}*f*

_{i}*t*+

*ϕ*) and cos(2π

_{i}*f*

_{i}*t*+

*ϕ*) by a simple matrix multiplication at each time step.

_{i}This mode offers reduced computational load, but is subject to drift over time due to cumulative quantization error. Because the method is not contingent on an absolute time value, there is no danger of discontinuity during extended operations, when an absolute time variable might overflow.

## Extended Capabilities

### C/C++ Code Generation

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

Usage notes and limitations:

This object has no tunable properties for code generation.

See System Objects in MATLAB Code Generation (MATLAB Coder).

## Version History

**Introduced in R2012a**

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