Analyze Menu
ToDo Produce separate documentation pages for the following Analyzers and accordingly reduce this page to a similar structure to the Effect Menu page.
- Contrast
- Plot Spectrum
- Find Clipping
- Beat Finder
- Regular Interval Labels
- Sample Analyze Nyquist Plug-in
- Sample Data Export - already has its own page
- Silence Finder & Sound Finder on a unified page together
- I propose to leave the section "Vamp Analysis Plug-ins" as-is on this page.
Ed 15Nov12: I would also leave the "Sample Analyze Nyquist Plug-in" bit on this page.
Built-in analysis tools
Most of the analysis tools included 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.
Contrast...
Contrast Analysis 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.
Plot Spectrum...
This 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). You can reduce the lowest displayable dB range by lowering the default -60 dB value for "Meter/Waveform dB range" in the Interface Preferences.
Find Clipping...
Displays runs of clipped samples in a Label Track, as a screen-reader accessible alternative to . A run must include at least one clipped sample, but may include unclipped samples too.
Start Threshold (default 3 samples) is the number of contiguous clipped samples that must be present before they will be labeled as an individual run. The higher the threshold, the less likely a clipped region will be recognized and the fewer labels that will be generated.
Stop Threshold (default 3 samples) is the number of contiguous unclipped samples that must be present before the run of clipped samples will be terminated. The higher the threshold, the longer a clipped region will be and the fewer labels that will be generated.
Each individual run of clipped samples is marked in the format "number of number". For example, "11 of 11" means there are 11 samples in this run of clipped samples and all of them are clipped, while "9 of 11" means only nine samples in the run of 11 are clipped. Note that in the case of a stereo track, each channel will have its own label, so if at one point both channels are clipped, two labels will appear above each other.
Note that unlike Show Clipping or Meter Toolbar, "Find Clipping" is not automatic, so after any editing that affects volume, or after import or recording of a new track, Find Clipping must be run again. Labels from another run of Find Clipping will be added to the existing label track - close the label track using the [X] on the left of the track if you want to view only labels for the current clipping.
Beat Finder...
Beat Finder 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. If you don't get enough beats detected, try reducing the "Threshold Percentage" setting.
Regular Interval Labels...
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.
You can choose whether or not to add a sequential number for each label, whether the number comes before or after the label text, and the minimum number of digits to use in the label numbers. The default is to have minimum two digits before the label. With that setting, if you had 10 labels with "Label" as the label text, the first label would be "01Label" and the last would be "10Label". "Begin numbering from" lets you start the numbering sequence from any number, even a negative number if desired.
When labels are created by choosing the interval between the labels, by default the label interval is adjusted slightly if needs be so that all the audio segments are of equal length. If you wish the chosen label interval to be respected even if this makes the final audio segment unequal, set "Adjust label interval to fit length" to "No".
After running "Regular Interval Labels", choose to export all the files in one process based on the label points.
Sample Analyze Nyquist Plug-in
This is 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.
Sample Data Export...
Sample Data Export reads the values of successive samples from the selected audio and prints this data to a plain text, CSV or HTML file.
Silence Finder...
Silence Finder 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.
If labels are produced in the middle of tracks, increase the silence level and duration. If some tracks don't have a label between them, reduce the silence level and duration. See Setting Parameters for more help choosing values to place the labels correctly.
Sound Finder...
Sound Finder 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.
If any tracks have more than one label, increase the silence level and duration. If any labels extend into other tracks, reduce the silence level and duration.
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.
Currently Audacity cannot load Vamp plug-ins from the Audacity Plug-Ins folder. 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:
- $HOME/vamp
- $HOME/.vamp
- /usr/local/lib/vamp (user plug-ins)
- /usr/lib/vamp (system-wide plug-ins)
