dsppack - Filter Design and Analysis Tool for GNU Octave

A GUI-based tool for designing, analyzing, and testing IIR and FIR digital filters. Developed as a Diploma Project at UPT (Universitatea Politehnica Timisoara).

Author: Mihut Vlad
License: GPLv3+
Version: 1.2.0

• IIR Filter Design - Butterworth, Chebyshev Type I/II, Elliptic
• FIR Filter Design - Rectangular (untapered baseline), Hamming, Hanning, Blackman, Kaiser windows, Parks-McClellan, Least-Squares
• Filter Types - Low Pass, High Pass, Band Pass, Band Stop
• Interactive Pole-Zero Editor - Manually add poles and zeros on the unit circle to shape the filter
• Detailed Analysis - Magnitude, Phase, Group Delay, Impulse Response, Step Response, Pole-Zero Diagram
• Frequency Axis Toggle - Switch response plots between normalized (0 to pi rad/sample) and absolute (0 to Fs/2 Hz) frequency axes
• Stability Analysis - BIBO stability check with pole radius and margin indicators
• Specification Mask Overlay - Passband ripple (Rp) and stopband attenuation (Rs) visualization
• Filter Comparison - Overlay two filter responses side by side
• Audio Demo - Load WAV files, apply filters, play original/filtered, view spectrograms (frequency axis follows the same Hz/normalized setting; the loaded file stays in memory while you retune the design)
• Code Export - Generate MATLAB/Octave, C header, or Python/SciPy code
• Workspace Export - Push the designed coefficients to the Octave workspace (num_coeffs, den_coeffs, fs_val)
• Report Generation - Export a self-contained HTML report with all plots and specifications
• Save/Load - Persist filter designs as .fil files
• Presets - 12 built-in presets for common audio/signal processing tasks

• GNU Octave >= 6.0.0
• signal package >= 1.4.0

1. In Octave, install the package:

   pkg install -forge dsppack

2. Load the required packages:

   pkg load dsppack

3. Launch the tool:

   dsppack_launch

1. Clone or download the repository.

2. In Octave, install the package:

   pkg install ./dsppack/

3. Load the required packages:

   pkg load signal
   pkg load dsppack

4. Launch the tool:

   dsppack_launch

pkg list dsppack

You should see dsppack listed with version 1.2.0.

% Load dependencies
pkg load signal
pkg load dsppack

% Launch the GUI
dsppack_launch

1. Select a Preset from the dropdown (e.g., "Bass Isolation") or configure manually
2. Set the sampling frequency, cutoff frequency, filter order, architecture, type, and topology
3. Click DESIGN FILTER to compute and plot the filter response
4. Use the Freq Axis button (top right, above the magnitude plot) to switch the frequency axes between normalized units (0 to pi rad/sample) and absolute frequency (0 to Fs/2, labelled in Hz/kHz). The setting is shared with the Detailed Analysis window, which has the same button
5. Use the bottom bar buttons to access additional features:
   • COMPARE FILTERS - Compare two filter designs
   • GENERATE REPORT - Export an HTML report
   • AUDIO DEMO - Test the filter on real audio files

dsppack/
  COPYING                - GPLv3 license
  DESCRIPTION            - Octave package metadata
  INDEX                  - Octave package function index
  README.md              - This file
  doc/
    user_manual.md       - User manual
    code_walkthrough.txt - Line-by-line code explanation
  inst/
    dsppack_launch.m     - Main GUI entry point
    dsp_compute_filter.m - Filter computation (IIR + FIR)
    dsp_design_callback.m - Design button handler
    dsp_plot_response.m  - Magnitude/phase plotting
    dsp_check_stability.m - BIBO stability analysis
    dsp_compute_f3db.m   - -3 dB crossing computation
    dsp_filter_order.m   - Realized filter order (correct for FIR)
    dsp_topo_names.m     - Topology / method lists per architecture
    dsp_update_stability.m - Stability indicator strip update
    dsp_draw_mask.m      - Specification mask overlay
    dsp_draw_zplane.m    - Pole-zero plane rendering (P/Z editor)
    dsp_plot_pz.m        - zplane-style pole-zero diagram with multiplicities
    dsp_new_window.m     - Standard application window factory
    dsp_freq_ticks.m     - Frequency axis tick labelling (x or y, normalized or Hz)
    dsp_freq_xticks.m    - x-axis wrapper over dsp_freq_ticks
    dsp_freq_axis_hz.m   - Shared frequency-axis unit toggle state
    dsppack_version.m    - Package version, read from DESCRIPTION
    dsp_result_window.m  - Detailed analysis window
    dsp_compare_window.m - Filter comparison window
    dsp_audio_demo.m     - Audio demo window
    dsp_code_export.m    - Code generation (MATLAB/C/Python)
    dsp_generate_report.m - HTML report generation
    dsp_save_callback.m  - Save design to .fil
    dsp_load_callback.m  - Load design from .fil
    dsp_export_callback.m - Export coefficients to workspace
    dsppack_test.m       - Self-test suite
    fda_pz_editor.m      - Interactive pole-zero editor
    pz_tool.m            - Standalone pole-zero tool

Addresses the review in issue #2.

• New: Rectangular Window FIR method, added as the first entry in the FIR method list — the untapered baseline against which the other windows are judged. Existing FIR method indices shift by one; designs saved by earlier versions are remapped automatically on load.
• Fixed: the Filter Comparison window rejected most FIR filters. "Use Current" looked the method name up in a hardcoded IIR list, so anything past the fourth entry (Kaiser, Parks-McClellan, Least-Squares) raised an index error and the filter was never loaded. It now reads the live method list, and the label names the architecture too.
• Fixed: FIR filters reported order 0 in the detailed analysis window, the comparison metrics, and the report, because the order was taken from the denominator alone. The new dsp_filter_order helper reports the realized order everywhere.
• Fixed: the pole-zero diagram now follows zplane conventions. FIR filters show the poles they have at the origin (previously nothing was drawn, since their denominator has no roots), and coincident poles and zeros are drawn once and annotated with their occurrence number instead of stacking invisibly. Multiplicity is verified algebraically rather than inferred from how tightly the numerical roots cluster, which cannot distinguish a repeated root from genuinely close ones.
• Fixed: the step response is now a stem plot, like the impulse response, since it is equally a discrete series.
• Fixed: the -3 dB crossings follow the frequency-axis setting, reported in Hz/kHz when the axes are, in both the analysis window (live, on toggle) and the report.
• Fixed: the HTML report honours the frequency-axis setting for its magnitude, phase, and group-delay plots, and carries all of the analysis-window corrections above. It also reports the realized order, noting when an odd-order FIR high-pass or band-stop was raised to stay realizable.
• Improved: the Audio Demo spectrogram frequency axis is adjustable between Hz and normalized, with its own toggle button.
• Improved: the Audio Demo keeps the loaded audio in memory. Going back, changing the design and reopening the demo brings the same file straight back, re-filtered with the new coefficients. The cache lives and dies with the main window.
• Changed: designs are saved as .fil, not .mat. Octave's save always wrote its own text format regardless of the name, so the old files were never MATLAB MAT files — the extension was purely misleading. The version tag stamped into a design is now read from DESCRIPTION at runtime, so it can no longer drift (it had been stuck at dsppack-1.0.0). Designs saved by 1.1.x must be renamed to .fil to be loadable.
• Self-test suite extended to 36 tests, including a regression test for the comparison-window bug.

• Fixed major bug when designing a filter using the bandpass type with the methods Chebyshev I, Chebyshev II and Elliptic for IIR architecture

• New: frequency axis unit toggle. A Freq Axis button on the main screen and in the Detailed Analysis window switches every frequency axis between normalized units (0 to pi rad/sample) and absolute frequency (0 to Fs/2), with round tick values labelled in Hz or kHz. The setting is shared between the two windows, persists while the tool is open, and is honored by the spec-mask overlay. Implemented by the new dsp_freq_axis_hz helper (shared state) and an extended dsp_freq_xticks (tick placement).
• The Filter Comparison window deliberately keeps normalized units, since the two compared filters may have different sampling rates.
• User manual updated with the new control; README feature list, quick start, and file listing brought up to date.

• Initial releases: IIR/FIR filter designer with presets, detailed analysis window, interactive pole-zero editor, filter comparison, audio demo, specification mask overlay, save/load, code export, HTML report generation.

This project is licensed under the GNU General Public License v3.0. See COPYING for details.