# freqz

Frequency response of discrete-time filter System object

## Syntax

## Description

`[`

returns the complex frequency response
`h`

,`w`

]
= freqz(`sysobj`

)`h`

of the filter System object™, `sysobj`

. The vector `w`

contains
the frequencies (in radians/sample) at which the function evaluates the frequency
response. The frequency response is evaluated at 8192 points equally spaced around
the upper half of the unit circle.

`[`

returns the
complex frequency response of the filter System object and the corresponding frequencies at `h`

,`w`

]
= freqz(`sysobj`

,`n`

)`n`

points
equally spaced around the upper half of the unit circle.

`freqz`

uses the transfer function associated with the filter
to calculate the frequency response of the filter with the current coefficient
values.

## Examples

## Input Arguments

## Output Arguments

## Tips

There are several ways of analyzing the frequency response of filters.
`freqz`

accounts for quantization effects in the filter
coefficients, but does not account for quantization effects in filtering arithmetic. To
account for the quantization effects in filtering arithmetic, refer to function
`noisepsd`

.

## Algorithms

`freqz`

calculates the frequency response for a filter from the
filter transfer function *Hq*(*z*). The complex-valued
frequency response is calculated by evaluating
*Hq*(*e ^{j}^{ω}*)
at discrete values of

*w*specified by the syntax you use. The integer input argument

`n`

determines the number of equally-spaced points
around the upper half of the unit circle at which `freqz`

evaluates
the frequency response. The frequency ranges from 0 to π radians per sample when you do
not supply a sampling frequency as an input argument. When you supply the scalar
sampling frequency `fs`

as an input argument to
`freqz`

, the frequency ranges from 0 to `fs`

/2
Hz.## Version History

**Introduced in R2011a**