# freqz

Compute digital filter frequency response values.

## Syntax

h = freqz(b,a,f,fs)

[h,f] = freqz(...)

## Inputs

`b`- The numerator polynomial coefficients of the filter.
`a`- The denominator polynomial coefficients of the filter.
`f`- The frequencies (in Hz) at which the response is computed.
- fs
- The sampling frequency (in Hz).

## Outputs

- h
- The frequency response values.
`f`- The frequencies (in Hz) at which the response is computed.

## Example

Verify the cutoff frequency of a fourth order Butterworth low pass digital filter with a 300 Hz cutoff frequency and a 1000 Hz sampling frequency.

```
b = [0.16718, 0.66872, 1.0031, 0.66872, 0.16718];
a = [1, 0.7821, 0.67998, 0.18268, 0.030119];
h = freqz(b,a,300,1000);
abs(h)
```

`ans = 0.70715`

## Comments

A warning is issued if values of `f` exceed the Nyquist frequency.