Arbitrary response magnitude and phase filter specification object

`d = fdesign.arbmagnphase`

d = fdesign.arbmagnphase(specification)

d = fdesign.arbmagnphase(specification,specvalue1,specvalue2,...)

d = fdesign.arbmagnphase(specvalue1,specvalue2,specvalue3)

d = fdesign.arbmagnphase(...,fs)

`d = fdesign.arbmagnphase`

constructs
an arbitrary magnitude filter specification object `d`

.

`d = fdesign.arbmagnphase(specification)`

initializes
the `Specification`

property for specifications
object `d`

to the string in `specification`

.
The input argument `specification`

must be one of
the strings shown in the following table. Specification strings are
not case sensitive.

Specification String | Description of Resulting Filter |
---|---|

| Single band design (default). FIR and IIR ( |

| FIR multiband design where |

| IIR single band design. |

The following table describes the arguments in the strings.

Argument | Description |
---|---|

| Number of bands in the multiband filter. |

| Frequency vector. Frequency values specified in |

| Complex frequency response values. |

| Filter order for FIR filters and the numerator and denominator
orders for IIR filters (when not specified by |

| Numerator order for IIR filters. |

| Denominator order for IIR filter designs. |

By default, this method assumes that all frequency specifications are supplied in normalized frequency.

`f`

and `h`

are the input
arguments you use to define the filter response desired. Each frequency
value you specify in `f`

must have a corresponding
response value in `h`

. This example creates a filter
with two passbands (`b`

= `4`

) and shows how `f`

and `h`

are
related. This example is for illustration only. It is not an actual
filter.

Define the frequency vector `f`

as ```
[0
0.1 0.2 0.4 0.5 0.6 0.9 1.0]
```

Define the response vector `h`

as ```
[0
0.5 0.5 0.1 0.1 0.8 0.8 0]
```

These specifications connect`f`

and `h`

as
shown in the following table.

f (Normalized Frequency) | h (Response Desired at f) |
---|---|

0 | 0 |

0.1 | 0.5 |

0.2 | 0.5 |

0.4 | 0.1 |

0.5 | 0.1 |

0.6 | 0.8 |

0.9 | 0.8 |

1.0 | 0.0 |

A response with two passbands—one roughly between 0.1
and 0.2 and the second between 0.6 and 0.9—results from the
mapping between `f`

and `h`

. Plotting `f`

and `h`

yields
the following figure that resembles a filter with two passbands.

The second example in Examples shows this plot in more detail
with a complex filter response for `h`

. In the example, `h`

uses
complex values for the response.

Different specification types often have different design methods
available. Use `designmethods`

`(d)`

to
get a list of design methods available for a given specification string
and specifications object.

`d = fdesign.arbmagnphase(specification,specvalue1,specvalue2,...)`

initializes
the filter specification object with `specvalue1`

, `specvalue2`

,
and so on. Use `get(d,'description')`

for descriptions
of the various specifications `specvalue1`

, `specvalue2`

,
...`spec`

* n*.

`d = fdesign.arbmagnphase(specvalue1,specvalue2,specvalue3)`

uses
the default specification string `n,f,h`

, setting
the filter order, filter frequency vector, and the complex frequency
response vector to the values `specvalue1`

, `specvalue2`

,
and `specvalue3`

.

`d = fdesign.arbmagnphase(...,fs)`

specifies
the sampling frequency in Hz. All other frequency specifications are
also assumed to be in Hz when you specify `fs`

.

Use `fdesign.arbmagnphase`

to model a complex
analog filter:

d=fdesign.arbmagnphase('n,f,h',100); % N=100, f and h set to defaults. design(d,'freqsamp');

For a more complex example, design a bandpass filter with low
group delay by specifying the desired delay and using `f`

and `h`

to
define the filter bands.

n = 50; % Group delay of a linear phase filter would be 25. gd = 12; % Set the desired group delay for the filter. f1=linspace(0,.25,30); % Define the first stopband frequencies. f2=linspace(.3,.56,40);% Define the passband frequencies. f3=linspace(.62,1,30); % Define the second stopband frequencies. h1 = zeros(size(f1)); % Specify the filter response at the freqs in f1. h2 = exp(-1j*pi*gd*f2); % Specify the filter response at the freqs in f2. h3 = zeros(size(f3)); % Specify the response at the freqs in f3. d=fdesign.arbmagnphase('n,b,f,h',50,3,f1,h1,f2,h2,f3,h3); D = design(d,'equiripple'); fvtool(D,'Analysis','freq');

`design`

| `designmethods`

| `fdesign`

| `setspecs`

Was this topic helpful?