# zerophase

Zero-phase response of digital filter

## Syntax

## Description

`[`

returns the zero-phase response `Hr`

,`w`

] = zerophase(`b`

,`a`

)`Hr`

and the angular frequencies
`w`

at which the zero-phase response is computed, given a filter
defined by numerator coefficients `b`

and denominator coefficients
`a`

. The function evaluates the zero-phase response at
`512`

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

`[`

returns the zero-phase response for the digital filter `Hr`

,`w`

] = zerophase(`d`

)`d`

. Use `designfilt`

to generate `d`

based on frequency-response
specifications.

`zerophase(___)`

plots the
zero-phase response versus frequency. If you input the filter coefficients or second order
sections matrix, the function plots in the current figure window. If you input a `digitalFilter`

, the function displays the step response in **FVTool**.

**Note**

If the input to `zerophase`

is single precision, the function
calculates the zero-phase response using single-precision arithmetic. The output
`Hr`

is single precision.

## Examples

## Input Arguments

## Output Arguments

## References

[1] Antoniou, Andreas.
*Digital Filters*. New York: McGraw-Hill, Inc.,
1993.

## Version History

**Introduced before R2006a**

## See Also

`designfilt`

| `digitalFilter`

| `freqs`

| `freqz`

| FVTool | `grpdelay`

| `invfreqz`

| `phasedelay`

| `phasez `