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.
- Understanding audio quality and the effects of digital compression (e.g. MP3) on audio bandwidth
- Detecting problems in audio recording
- Teaching and training
- Speech and audio research
- General scientific applications
- Radio amateurs
Feature and Specifications
- Runs under Microsoft Windows 95, Windows XP, Windows Vista, Windows 7
- 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 2048-sample FFT with Hanning (raised-cosine) window-function.
- Choice of linear and logarithmic (dB) vertical scales (including 'perceptual' A-weighted scales**)
- 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).
** In the present implementation 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.
A future implementation may use actual A-weighting - but the existing setting still rolls off the high and
low frequencies to yeild a result more perceptual than the raw FFT output.
Features not yet implemented, but under consideration (roughly in order of likely implementation)
- Stereo vector analyser
- Grid-line option on the spectral display
- Labelling/readout of precise frequency (and amplitude/energy) of prominent spectral peaks
- User-selection of different transform sizes to trade-off time response and spectral resolution.
- Horizontal scroll option to allow close-up inspection of a narrow part of the spectrum.
- Time-averaged spectral displays
Download: SpecAn_3v5.exe (532kB) new version 3.5 - August 2013.
This version adds STEREO input and fixes a bug with the amplitude for linear vertical scales
which was accidentally introduced in version 3.0.
By downloading this file, you consent to the
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: 25 Aug 2013
©2013 William Andrew Steer