Alsa-Nyser is an Real Time Audio Analyser that displays several informations about sound as: Signals of the channels, Phase of sound in 1D and 2D representation, Spectrum in full band, pectrum in 1/3 octavia displaying frequency in Stereo or Mono, Frequency of the peak signal, and Stereo Meters.
Cthugha is a free program available for PC's (running DOS, Windows, or Linux) and Macintosh's which takes sound input from a CD, stereo, or microphone and displays colorful animated graphics synced to the sound.
DireShow performs a light show on a 16 bit music PCM stream.
Dissociated Studio plays through a piece of music, every once in a while jumping from one similar (as determined by FFTs) bit to another.
Xtace is a Audio Visualization plugin for the X-Window System. It connects to ESD (Enlightened Sound Daemon) and displays the audio data as either a pseudo 3D flying landscape, pseudo 3D pointed landscape, 16-256 channel graphic EQ, multi-mode Oscilloscopes, Horizontal Spectrogram, or a combination Hi-res FFT with a Vertical Spectrogram.
Fluxus allows you to write Scheme scripts that create graphics live, interpreting audio and OSC input as a source of animation data. Fluxus also uses a fully featured physics library, which means you can script physical properties into objects and simulate them in realtime. Released for Linux under the GPL licence.
Kodisein was written and designed for one purpose mainly: to be a VJ (VideoJockey) tool. That means: it should be used in discotheques to supplement the music with matching visuals.
Osqoop is an open source software oscilloscope. It features an arbitrary number of channels and long acquisition durations. Signal processing and external peripherals control is possible through a plugin architecture. Data sources are plugins as well.
projectM is a music visualizer which uses 3D hardware accelerated iterative image based rendering. projectM is basically a reimplementation of Milkdrop under OpenGL. projectM already does some things Milkdrop does not (like infinite custom shapes/waves).
QOscC is a highly flexible and configurable software Oscilloscope with a large number of features. This includes support for any number of audio devices (ALSA or OSS), each with any number of channels. Each scope display can be configured individually to different display types and variants. e.g. you can chose from standard y-t mode (as on an usual oscilloscope), xy mode (e.g. for measuring the phase shift between two signals) of the FFT mode (to view a spectrum plot of the signal).
sndpeek is a light-weight app which performs feature extraction on audio files or live audio input with real-time display of waveform, spectrum, and features.
SonaSound is a real-time music visualisation tool using either soundcard input or playing files to the soundcard output. It features a waveform-, a short-time spectral- and a sonogram display for music application. It tries to be as accurate as possible, not as beautiful as possible. You can easily transcribe music via the superimposed tuneable (you can adjust the reference "A"'s frequency) staff lines using LPC to generate the spectrum. On the other hand a scientific apporach is possible as well when using the FFT to generate the spectrum and disable the staff lines.
SoundMan is a frequency analyzer. It can computes the frequency spectrum in realtime. And you can try to filter one or more frequency components. It can compute a spectogram too. It requires Qt-1.4 and an OSS driver.
Waterfall Spectrum Analyzer
Waterfall is yet another XMMS spectrum analyzer. While most analyzers only show a changing snapshot of the current sound, waterfall shows a scrolling spectrogram, a 2-d plot of frequency vs time, with energy represented by intensity. There are also options to use color to display stereo discrepancies, frequency onsets, or frequency uniformity.
WMscope is a little applet that docks under WindowMaker or Afterstep and will display audio data or a neat sine wave type thingy.
XAnalyser is a program to analyse a stereo audio signal. It has two displays: Frequency Spectrum, and XY Scope.
XSpectrum is a simple but powerful real-time spectrum analyzer for Linux with X11R6. It use highly efficient Radix-2 and Radix-4 floating point FFT algorithms. The soundcard is used as the digitizing device.