Filter Design Toolbox

Working with Quantized Filters

This chapter covers what you need to know to construct and use quantized filters:

• Constructing quantized filters
• Quantized filter properties
• Filtering data with quantized filters
• Transformation Functions for Quantized Filter Coefficients

The quantized filters you create in this toolbox are objects with properties. Most of the basic information you need to know about setting and retrieving property values is found in Working with Objects.

Constructing Quantized Filters

You can construct quantized filters in the Filter Design Toolbox by either:

• Using the quantized filter constructor function qfilt
• Copying an existing one

All filter characteristics are stored as properties that you can set or retrieve. Some of these quantized filter characteristics include:

• Filter structure.
• Reference filter coefficients.
• Filter topology (single section or cascaded nth-order sections). The syntax you use to enter the reference filter coefficients determines the topology.
• Quantized filter data format parameters:
• Quantization parameters (precisions).
• Data type (signed or unsigned fixed-point, or, double-, single-, or custom-precision floating-point).
• Rounding method used in quantization.
• Overflow method used in quantization.
• Scaling factors for each section of a cascade of nth-order sections.

You can specify quantized filter properties by either:

• Specifying all of the filter properties when you create it
• Creating a quantized filter with default property values, and changing some or all of these property values later

Constructor for Quantized Filters

The most direct way to create a quantized filter (Qfilt object) is to create one with the default properties. You create a default quantized filter Hq by typing

• Hq = qfilt
  

A listing of all of the properties of the filter Hq you just created is displayed along with the associated property values. All property values are set to defaults when you construct a quantized filter this way.

To construct a quantized filter with properties other than the default values, follow the procedure outlined in Setting Property Values Directly at Construction.

For some examples of using the quantized filter constructor to construct a filter while specifying some properties at construction, see:

• Constructing an Eight-Bit Quantized Filter
• Example -- Accessing Coefficient Information from Filters with One Section
• Example -- Accessing Coefficient Information from Multisection Filters

Quantizer Data Functions

Constructing a Quantized Filter from a Reference