freq

Generate a vector of frequency locations.

Syntax

f = freq(time)

f = freq(n,fs)

f = freq(..., option)

Inputs

time
A vector of equally spaced times.
Type: double
Dimension: vector
n
The number of points in the two-sided spectrum.
Type: integer
Dimension: scalar
fs
The sampling frequency.
Type: double
Dimension: scalar
option
'twosided'
Full range is produced, with 'negative' frequencies to the right of the centered Nyquist value.
'onesided'
Only non-negative frequencies are created.
'shift'
Full range is produced, with 'negative' frequencies to the left of the centered DC value.
Type: string

Outputs

f
The vector of frequencies.

Examples

Example with time vector:

f = freq([0:0.001:0.009])
f = [Matrix] 1 x 10
0  100  200  300  400  500  600  700  800  900
Example with sampling frequency and 'shift' option specified:
f = freq(10,1000,'shift')
f = [Matrix] 1 x 10
-500  -400  -300  -200  -100  0  100  200  300  400

freq is typically used to create x axis values for a plot with FFT related frequency domain data. The most common y dimensions are FFT magnitudes and PSD values.

For an odd number of points, the Nyquist frequency falls between two other values and is not contained in the output.

For an even number of points, the 'shift' option regards the Nyquist frequency as a negative value. This is for consistency with fftshift.

For the 'onesided' option, the number of output points will be fix(n/2+1), and n otherwise.