by W.A. Steer  PhD

Audio Spectrum Analyser

This page describes a free audio spectrum analyser which you can download. It uses fast Fourier transform (FFT) to give a real-time ('live') spectrum display on your screen.

Applications

• Understanding audio quality and the effects of digital compression (e.g. MP3) on audio bandwidth
• Detecting problems in audio recording
• Identifying problems with audio processing, e.g. in laptop beamforming-microphone algorithms/drivers
• Teaching and training
• Speech and audio research
• General scientific applications
• Acoustic noise analysis and R&D into making quieter appliances
• Radio amateurs

Feature and Specifications

• Runs under Microsoft Windows 95, Windows XP, Windows Vista, Windows 7 and newer.
• Samples an audio stream in 16-bit stereo, then uses a Fast Fourier Transform to yield the spectral analysis in real time.
• Bargraph peak-level indicator shows time-domain peak levels and onset of clipping distortion (spectrum also goes red).
• Stereo input, dual bargraph, choice of Left, Right, sum or difference for frequency analysis
• User selection of sampling-rates, including 32kHz, 44.1kHz, 48kHz
• Supports multiple 'wave input' devices (multiple soundcards, and/or the newer Windows Vista/7 sound model).
• Spectrum obtained using FFT with Hanning (raised-cosine) window-function.
• User-selection of different FFT transform sizes to trade-off time response and spectral resolution. New in v3.7
• Choice of linear and logarithmic (dB) vertical scales (including 'perceptual' A-weighted scales)
• Implemented correct 'A'-weighted displays (rather than Fletcher-Munson/Terhardt). Now optional for all visualisations.
• Vertical scale calibrated as fraction of digital full scale ('FS') with currently-set mixer-settings etc.
• Choice of horizontal (frequency) scales, including a logarithmic 'perceptual' scale.
• Spectrograph (waterfall) visualisation options (experimental/beta feature).
• Time-averaged spectral displays. New in v3.8
• Self-test / demo mode, showing spectral purity and effects of windowing. New in v3.86
• Option to use a couple of alternative FFT window-functions
• Ability to export some spectral data to clipboard (additional improvements/disambiguations in v. 3.97)
• Third-octave band analysis (v3.97)
• Mel-band analysis (v3.97 - non-overlapping frequency bands)

In older versions the perceptual "A-weighted" is not actually A-weighted, but is modified by the hearing threshold according to Terhardt - see http://www.diracdelta.co.uk/science/source/t/h/threshold%20of%20hearing/source.html. Versions 3.8 onwards use actual A-weighting.

Features not yet implemented, but under consideration (roughly in order of likely implementation)

• Improvements to export/save spectral data functionality
• Improve axis displays in general, and add proper time axis/scales to spectrogram visualisations
• Labelling/readout of precise frequency (and amplitude/energy) of prominent spectral peaks
• Ability to open, play, and analyse directly from uncompressed .WAV files
• Option to calibrate vertical scale, e.g. to 94dB 1kHz reference source (maybe in a future Pro/paid version)
• Tidy up the stereo vector analyser visualisation
• 'Oscilloscope' visualisation
• Tweaks for better window layout/rendering under Windows 10
• Option to pause display and step back/forward though the past few seconds (and maybe a peak-hold function)
• Use lookup tables to improve program efficiency for any displays using log calculations!
• Grid-line option on the spectral display
• Horizontal scroll option to allow close-up inspection of a narrow part of the spectrum.
• ...

Download

Download: SpecAn_3v97c.exe (564kB) latest version 3.97c - 16 July 2016.

New in this version: improvements to ability to export numerical data (time-average FFT) to clipboard, new third-octave band analysis, Mel-band analysis, and other minor tweaks.

Older/archive versions

Download: SpecAn_3v93.exe (553kB) previous version 3.93 - 29 April 2016.

Download: SpecAn_3v91.exe (550kB) older version 3.91 - 29 August 2015.

Download: SpecAn_3v5.exe (532kB) much older version 3.5 - August 2013.

By downloading any of these files, you consent to the standard disclaimer.

This applet doesn't require any installation, won't touch your Windows Registry, and won't install any DLLs. Just download the .EXE and run it. There's no bundled adware or unwanted toolbars. It'll even run straight off a USB memory stick if you want.

Created: May 2011
Last modified: 1 Aug 2016
Source: http://www.techmind.org/audio/specanaly.html