From Audacity Development Manual
Although by default, no keyboard shortcuts are provided for most of the analysis tools, it is possible to set up your own shortcut for any Analyze command. For instructions on how to do this please see Keyboard Preferences.
Built-in analysis tools
- Most of the analysis tools shipped in Audacity are Nyquist plug-ins. You can download some additional Nyquist analysis plug-ins from the Download Nyquist Plug-ins page on our Wiki. Some LADSPA analysis plug-ins for Linux can be downloaded from the LADSPA site.
- Where a shipped analysis tool has settings, its description page (accessed by the links below) shows an image of the interface and its default settings.
Contrast... CTRL + SHIFT + T
Analyzes a selected, single non-stereo audio track to determine the average rms difference in volume (contrast) between foreground (the speech) and background (music, audience noise or similar). The purpose is to determine if the speech will be intelligible to the hard of hearing.
Takes the selected audio (which is a set of sound pressure values at points in time) and converts it to a graph of frequencies (the horizontal scale in Hz) against amplitudes (the vertical scale in dB).
Attempts to place labels at beats which are much louder than the surrounding audio. It's a fairly rough and ready tool, and won't necessarily work well on a typical modern pop music track with compressed dynamic range.
Places labels in a long track so as to divide it into smaller, equally sized segments. For example, this can be useful for distributing a large file on the internet. You can either choose the number of labels to be created, or the interval between them. Each label produced contains the chosen label text.
Sample Analyze Nyquist Plug-in
An example of a Nyquist analyze plug-in (this only ships with the Mac OS X version of Audacity). All it does is put labels at the start and end of the selection. If you are interested in writing Nyquist analyze plug-ins, this provides a simple starting point. Open the "analyze.ny" file (found in the "Plug-ins" folder) in a text editor to see the Nyquist code. For more information on the Nyquist programming language and how to use it within Audacity, see Audacity and Nyquist and Nyquist in Audacity.
Reads the values of successive samples from the selected audio and prints this data to a plain text, CSV or HTML file.
Divides a track up by placing point labels inside areas of silence. Use this if you just want to split the recording into tracks at a specific point without removing the silences between them.
Divides a track up by placing region labels for areas of sound that are separated by silence. Use this to make the labels show the exact region of each track to be exported. This lets you remove some or all of the silence between the tracks.
Vamp Analysis Plug-ins
You can also add some additional analysis tools in the Vamp plug-in format for viewing and analysing the descriptive contents of music audio files. Typical things that a Vamp plug-in might calculate include the locations of moments such as note onset times and power or fundamental frequency data.
To run a Vamp plug-in, select the audio and run the plug-in from the menu. An annotated label track appears showing the result. At this time, Audacity cannot display graphical output such as histograms or curves.
Vamp plug-ins are loaded from the standard directories defined by the Vamp SDK as follows:
- On all platforms: any directories listed in the VAMP_PATH environment variable
- additionally on Windows:
- %%PROGRAMFILES%%\Vamp Plugins (a directory named "Vamp Plugins" within the system Program Files directory, however localized and on whatever drive is relevant to this install of Windows)
- additionally on OS X:
- ~/Library/Audio/Plug-Ins/Vamp (user plug-ins)
- /Library/Audio/Plug-Ins/Vamp (system-wide plug-ins)
- additionally on Linux/Unix:
- /usr/local/lib/vamp (user plug-ins)
- /usr/lib/vamp (system-wide plug-ins)