Pure Data (Pd) is a graphical programming language and environment for audio, video and multimedia.
It is written by Miller S. Puckette and a worldwide community of developers and users.
Pd is open source software and runs on many operating systems can can be downloaded here.
Here are some Pd files which are of possible use for you, released under the BSD license.

lecteur~.pd     memoire.pd     help-patch     example-soundfile     screenshot
lecteur~.pd is an abstraction to play back audio data in flexible ways. It requires memoire.pd

rpdb~.pd     help-patch and screenshot
RMS and Peak Dezibel metering abstraction (Pd Version 0.50-2 and later required).

faderRms.pd     help-patch and screenshot
Abstraction to convert fader values to gain values with a curve similar to audio mixing desks.

gem_vu.pd     help-patch and screenshot
An abstraction to visualize a vu-meter (like pd's internal object) using the Gem opengl library.
When monitoring a lot of channels this can save some cpu compared to Pd's internal vu object.

MUSGER - Script-based audio processing

MUSGER is a library of audio processing functions for Unix-like operating systems executed in a shell command window.
It is conceived as a modular collection of scripts using SoX, aubio, CDP.
MUSGER is released under the GNU/GPL license and is named after August Musger who invented a slow motion technique for film in 1904.