Digital Filter Design

Design and implement digital FIR and IIR filters

• Library:

• DSP System Toolbox / Filtering / Filter Implementations

• 

Description

Use this block to design, analyze, and efficiently implement floating-point filters.

The Digital Filter Design block implements a digital Finite Impulse Response (FIR) or Infinite Impulse Response (IIR) filter that you design by using the Filter Designer (filterDesigner) app. This block provides the same filter implementation as the Discrete FIR Filter or Biquad Filter blocks.

You must specify whether the block performs frame-based or sample-based processing on the input by setting the Input processing parameter. The block applies the specified filter to each channel of a discrete-time input signal and outputs the result. The outputs of the block numerically match the outputs of the Discrete FIR Filter or Biquad Filter block and the MATLAB^® filter function. For more information, see Getting Started with Filter Designer.

These blocks also implement digital filters, but serve slightly different purposes:

• Discrete FIR Filter (Simulink) and Biquad Filter— Use to efficiently implement floating-point or fixed-point filters that you have already designed. These blocks provide the same exact filter implementation as the Digital Filter Design block.

• Filter Realization Wizard — Use to implement floating-point or fixed-point filters built from Sum, Gain, and Unit Delay blocks. You can either design the filter within this block, or import the coefficients of a filter that you designed elsewhere.

Ports

Input

Port_1 — Input signal

vector | matrix

Signal to filter, specified as a vector or matrix of real values. When given matrix input, the block treats each column as an independent channel.

The sample rate, Fs, that you specify in the filter designer app must be identical to the sample rate of the input to the Digital Filter Design block. When the sampling frequencies do not match, the Digital Filter Design block returns a warning message and inherits the sample rate of the input block.

Data Types: single | double

Output

Port_1 — Output signal

vector | matrix

Filtered signal, returned as a vector or a matrix of real values.

Data Types: single | double

Parameters

Dialog Box

For more information about the parameters in this dialog box, see Getting Started with Filter Designer.

Model Examples

Display Frequency-Domain Data in Spectrum Analyzer

Use a Spectrum Analyzer block to display the frequency content of two frame-based signals simultaneously. The Spectrum Analyzer block computes the Fast Fourier Transform (FFT) of the input signal internally, transforming the signal into the frequency domain.

Block Characteristics

Data Types	double | single
Multidimensional Signals	No
Variable-Size Signals	No

More About

Designing the Filter

To open filter designer, double-click the Digital Filter Design block. Use the filter designer to design or import a digital FIR or IIR filter. To learn how to design filters with this block and filter designer, see:

• Digital Filter Design Block

• Filter Designer app reference page. For details, see filterDesigner.

Tuning the Filter During Simulation

You can tune the filter specifications in filter designer during simulations if your changes do not modify the filter length or filter order. As you apply any filter changes in filter designer, the filter is updated.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using Simulink® Coder™.

Generated code relies on memcpy or memset functions (string.h) under certain conditions.

The Digital Filter Design block supports SIMD code generation using Intel AVX2 technology under these conditions:

• Input processing is set to Columns as channels (frame based).

• Filter Structure (in Import Filter from Workspace pane) is set to Direct-Form FIR. You can generate SIMD code even when the filter is a Direct-Form FIR Transposed filter. To create a Direct-Form FIR Transposed filter, select Edit > Convert Structure, and click Direct-Form FIR Transposed.

• Input signal has a data type of single or double.

The SIMD technology significantly improves the performance of the generated code.