Documentation

### This is machine translation

Translated by
Mouseover text to see original. Click the button below to return to the English version of the page.

# centfrq

Wavelet center frequency

## Syntax

```FREQ = centfrq('wname') FREQ = centfrq('wname',ITER) [FREQ,XVAL,RECFREQ] = centfrq('wname',ITER,'plot') ```

## Description

`FREQ = centfrq('wname')` returns the center frequency in hertz of the wavelet function, `'wname'` (see `wavefun` for more information).

For `FREQ = centfrq('wname',ITER)`, `ITER` is the number of iterations performed by the function `wavefun`, which is used to compute the wavelet.

`[FREQ,XVAL,RECFREQ] = centfrq('wname',ITER,'plot')` returns, in addition, the associated center frequency based approximation `RECFREQ` on the 2ITER points grid `XVAL` and plots the wavelet function and `RECFREQ`.

## Examples

collapse all

This example shows how to determine the center frequency in hertz for Daubechies' least-asymmetric wavelet with 4 vanishing moments.

`cfreq = centfrq('sym4');`

Obtain the wavelet and create a sine wave with a frequency equal to the center frequency, `cfreq`, of the wavelet. Use a starting phase of $-\pi$ for the sine wave to visualize how the oscillation in the sine wave matches the oscillation in the wavelet.

```[~,psi,xval] = wavefun('sym4'); y = cos(2*pi*cfreq*xval-pi); plot(xval,psi,'linewidth',2); hold on; plot(xval,y,'r');```

This example shows to convert scales to frequencies for the Morlet wavelet. There is an approximate inverse relationship between scale and frequency. Specifically, scale is inversely proportional to frequency with the constant of proportionality being the center frequency of the wavelet.

Construct a vector of scales with 32 voices per octave over 5 octaves for data sampled at 1 kHz.

```Fs = 1000; numvoices = 32; a0 = 2^(1/numvoices); numoctaves = 5; scales = a0.^(numvoices:numvoices*numoctaves).*1/Fs;```

Convert the scales to approximate frequencies in hertz for the Morlet wavelet.

`Frq = centfrq('morl')./scales;`

You can also use `scal2frq` to convert scales to approximate frequencies in hertz.