audioprism 
audioprism is a spectrogram tool for PulseAudio and WAV files.
Examples
Music
CW/Morse
RTTY
A segment of Aphex Twin's equation song
$ sox Aphex\ Twin\ -\ Equation.mp3 equation_segment.wav trim 5:26.5 11
$ ./audioprism --orientation horizontal equation_segment.wav equation_spectrogram.png
Usage
$ audioprism
In real-time mode, audioprism renders the spectrogram of a PulseAudio input source to an SDL window. The pavucontrol mixer can be used to select the audio input source. PulseAudio provides loopback "monitors" of audio outputs as audio input sources, so audioprism can be used with audio streams playing from another program.
$ audioprism test.wav test.png
In WAV file mode, audioprism renders the spectrogram of a WAV file to an image file. The output file can be any kind of image format supported by GraphicsMagick, determined by its file extension.
$ audioprism --help
Real-time Usage: ./audioprism [options]
WAV File Usage: ./audioprism [options] <WAV file input> <image file output>
Interface Settings
-h,--help Help
--fullscreen Fullscreen mode
--width <width> Width of spectrogram (default 640)
--height <height> Height of spectrogram (default 480)
--orientation <orientation> Orientation [horizontal, vertical]
(default vertical)
Audio Settings
-r,--sample-rate <rate> Audio input sample rate (default 24000)
DFT Settings
--overlap <percentage> Samples overlap percentage (default 50)
--dft-size <size> DFT Size, must be power of two (default 1024)
--window <window function> Window Function [hann, hamming, bartlett, rectangular]
(default hann)
Spectrogram Settings
--magnitude-scale <scale> Magnitude Scale [linear, logarithmic]
(default logarithmic)
--magnitude-min <value> Magnitude Minimum (default 0.0)
--magnitude-max <value> Magnitude Maximum (default 50.0)
--colors <color scheme> Color Scheme [heat, blue, grayscale]
(default heat)
Interactive Keyboard Control:
q Quit
f Toggle fullscreen
h Hide/show help
s Hide/show settings
d Hide/show debug stats
c Cycle color scheme
w Cycle window function
l Cycle linear/log magnitude
- Decrease min magnitude
= Increase min magnitude
[ Decrease max magnitude
] Increase max magnitude
Left Decrease DFT size
Right Increase DFT size
Down Decrease overlap
Up Increase overlap
audioprism v1.1.0 - https://github.com/vsergeev/audioprism
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Building
Arch Linux users can install audioprism with the AUR package audioprism.
audioprism depends on: PulseAudio, FFTW3, SDL2, SDL2_ttf, libsndfile, GraphicsMagick, and a C++11 compiler.
# Ubuntu/Debian
sudo apt-get install libpulse-dev libfftw3-dev libsdl2-dev libsdl2-ttf-dev libsndfile1-dev libgraphicsmagick++1-dev
# Fedora/RedHat
sudo yum install pulseaudio-libs-devel fftw-devel SDL2-devel SDL2_ttf-devel libsndfile-devel GraphicsMagick-c++-devel
# ArchLinux
sudo pacman -S libpulse fftw sdl2 sdl2_ttf libsndfile graphicsmagick
git clone https://github.com/vsergeev/audioprism.git
cd audioprism
make
sudo make install
License
audioprism is GPLv3 licensed. See the included LICENSE file for more details.