Filter Design Toolbox Release Notes

Chapter 3
Filter Design Toolbox 2.0 Release Notes

New Features

Incorporating functionality from the Quantized Filtering Toolbox, Filter Design Toolbox 2.0 is a new product for digital filter design, implementation, and analysis using fixed-point or arbitrary-precision floating-point arithmetic. This toolbox includes advanced FIR and IIR filter design methods and a new quantization tool for designing and analyzing quantized FIR and IIR filters. This section introduces the features and enhancements added in the Filter Design Toolbox 2.0 since the Quantized Filtering Toolbox 1.0 was released in Release 11.1.

Note    The Quantized Filtering Toolbox 1.1 has been integrated into the Filter Design Toolbox 2.0. The information below summarizes the changes to the Quantized Filtering Toolbox since Version 1.0 of that product. These changes are incorporated into the new Filter Design Toolbox 2.0.

You must have the Signal Processing Toolbox installed to use Filter Design Toolbox.

New Quantization Tool for Advanced FIR and IIR Filter Design

Signal Processing Toolbox includes an interactive filter design tool called Filter Design and Analysis Tool (FDATool). You use this visual interface to design, convert, quantize, import, and export FIR and IIR filters. FDATool integrates filter design and analysis functions in a single tool, letting you do all your filter design tasks from within the tool instead of using the MATLAB command line. Filter Design Toolbox adds quantization analysis to FDATool.

When you install Filter Design Toolbox, FDATool operates in three modes:

• Filter Design for designing double-precision FIR and IIR filters.
• Import for importing existing filters from your MATLAB workspace or by entering an expression.
• Quantization for quantizing filters in FDATool. You can quantize any filter in FDATool, whether you designed or imported the filter.

To enable you to convert filters from one structure to another, for example, from direct form to coupled allpass, FDATool offers smart conversion tools. When you convert a filter, FDATool offers you a selection of conversion structures that depends on the current filter type.

To launch FDATool, enter fdatool at the MATLAB command prompt or use the Launch Pad. For more information on the new tool, refer to "Filter Design and Analysis Tool" in the Signal Processing Toolbox User's Guide or use Help to review the online documentation.

New Objects

The Filter Design Toolbox 2.0 includes these new objects:

• Quantizer object

• Use the quantizer to quantize data using fixed-point or custom floating-point arithmetic. Use the quantizer function to construct a quantizer, and use the quantize function to quantize the data according to your quantizer specifications. There are also many functions that calculate the characteristics associated with a given quantizer. For example, eps determines the precision of the quantizer, and realmax determines the maximum number the quantizer can quantize without overflow.

• Quantized FFT object

• Use the new quantized FFT object to create and simulate fixed-point and custom floating-point FFTs. Construct a quantized FFT to specify the quantizing characteristics of the FFT method that you want to apply to data. Use the function qfft to construct a quantized FFT, and the function fft to apply an FFT to data as specified by your quantized FFT.

New Filter Design Functions

The Filter Design Toolbox 2.0 includes these new filter design functions:

• firlpnorm - Design a least P-norm FIR filter
• gremez - Use generalized Remez techniques to design FIR filters
• iirgrpdelay - IIR filter design with prescribed group delay value
• iirlpnorm - Design a least P-norm IIR filter
• iirlpnormc - Design a constrained least P-norm IIR filter

New Filter Conversion Functions

The Filter Design Toolbox 2.0 includes these new filter conversion functions:

• ca2tf - Convert coupled allpass transfer function forms to transfer function forms
• cl2tf - Convert coupled allpass lattice forms to transfer function forms
• iirpowcomp - Compute a power-complementary IIR filter from a given IIR filter
• sos: Convert the filter topology of a quantized filter to second-order sections with scaling
• tf2ca - Convert transfer function forms to coupled allpass transfer function forms
• tf2cl - Convert transfer function forms to coupled allpass lattice forms
• Quantized filter coefficient conversion

• You can now convert quantized filter coefficients to a hex or binary format, using these functions:
  • num2hex for hexadecimal conversion
  • num2bin for binary conversion

  These functions are overloaded for quantizers and quantized FFTs.

New Filter Structures

Filter Design Toolbox 2.0 includes five new filter structures:

• Direct form FIR transposed
• Direct form antisymmetric FIR
• Lattice coupled-allpass
• Second-order sections
• Lattice coupled-allpass power-complementary

To learn more about these structures, refer to Filter Structures in the Filter Design Toolbox User's Guide.

New Analysis Methods

Filter Design Toolbox 2.0 includes two new analysis methods:

• Limit Cycle - The new function limitcycle uses Monte Carlo techniques to detect limit cycles in quantized filters.
• Noise Loading Method - Use function nlm to use the noise loading method to calculate the frequency response of a quantized filter. Compare the response to the results from freqz, which calculates the theoretical frequency response. To generate noise signals that contain complete frequency content across the spectrum, nlm uses a series of Monte Carlo trials.

New Functions and Enhancements

Filter Design Toolbox 2.0 includes the following new functions and enhancements:

• Added copyobj function for copying quantized filters, quantized FFTs, and quantizers. Copies are independent of the original items, but have the same property values as the original.
• Changed the CoefficientFormat property to default to Quantizer rather than Unitquantizer for quantized filters, quantized FFTs, and quantizers.
• Added NOperations, a new data-related read-only property for quantizers that counts the number of data points quantized by a quantizer.
• Updated the quantized filter data display to indicate over- and underflow conditions in filter coefficients, as well as adding the NOperations read-only values to the displayed information.
• Changed the default rounding method for the CoefficientFormat property for quantized filters and FFTs to 'round' rather than 'floor'.
• Included new quantized filtering demos. Use the demo function to access the new demos.
• Modified the data format properties.
• You can now set the following properties individually for each data path in a quantizer, quantized filter, or quantized FFT:
• Mode
• RoundMode
• OverflowMode
• OptimizeUnityGains

Known Software and Documentation Problems

Upgrading from an Earlier Release