# filter

1-D digital filter

## Description

filters
the input data `y`

= filter(`b`

,`a`

,`x`

)`x`

using a rational transfer function defined
by the numerator and denominator coefficients `b`

and `a`

.

If `a(1)`

is not equal to `1`

,
then `filter`

normalizes the filter coefficients
by `a(1)`

. Therefore, `a(1)`

must
be nonzero.

If

`x`

is a vector, then`filter`

returns the filtered data as a vector of the same size as`x`

.If

`x`

is a matrix, then`filter`

acts along the first dimension and returns the filtered data for each column.If

`x`

is a multidimensional array, then`filter`

acts along the first array dimension whose size does not equal 1.

## Examples

## Input Arguments

## Output Arguments

## More About

## Tips

To use the

`filter`

function with the`b`

coefficients from an FIR filter, use`y = filter(b,1,x)`

.If you have Signal Processing Toolbox™, use

`y = filter(d,x)`

to filter an input signal`x`

with a`digitalFilter`

(Signal Processing Toolbox) object`d`

. To generate`d`

based on frequency-response specifications, use`designfilt`

(Signal Processing Toolbox).See Digital Filtering (Signal Processing Toolbox) for more on filtering functions.

## References

[1] Oppenheim, Alan V., Ronald W. Schafer,
and John R. Buck. *Discrete-Time Signal Processing*.
Upper Saddle River, NJ: Prentice-Hall, 1999.

## Extended Capabilities

**Introduced before R2006a**