Analyze Menu

Analyze contains tools for finding out about the characteristics of your audio, or labeling key features. Plug-ins that accept input but produce no output will also be placed in the Analyze menu.

ToDo Sort the table out

If we don't want table and cell borders with Wikitable class (and if we still use tables for layout, we probably don't) it looks if borders have to be turned off in Common.css if this behaves like other Wikis, but http://www.audacityteam.org/manual/index.php?title=MediaWiki:Common.css seems to have no content? I'll have to experiment/research further - Buanzo does not know either at the moment - Gale

Unless this table is merely a summary reference point, it isn't going to work - look at the text in plot spectrum alone (which is needed). Or is Plot Spectrum an "advanced" menu item (like some of the advanced effects) which has its own page? - Gale

Summary Reference. Yes. Track Pop-Down Menu has the right level of detail for a reference. Having more detail linked from it is icing on the cake. For example, the track pop down menu description doesn't show a screenshot of the dB view. It doesn't need to have it, but we could add it (as a link) if we want and have time to. The Plot Spectrum item is complex enough to merit a page, I think. I wouldn't be keen to have a page for Silence Finder, overkill, which is OK if we had unlimited resources, but we don't. - James

Menu	Description
	Plot Spectrum text Find Clipping text Beat Finder text Regular interval labels text Silence finder text Vamp Plug-ins will appear in this menu too, if they are installed.

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 against amplitudes. This is done using a complicated piece of maths known as a Fast Fourier Transform or FFT. This gives a value for each narrow band of frequencies that represents how much of those frequencies is present. All the values are then interpolated to create the graph. Note that currently only the first 23.8 seconds of selected audio can be analyzed.

The following drop-down boxes let you configure the way the plot is calculated:

Algorithm

Determines what type of processing is done on the audio data.

• Spectrum: (default) - Plots the FFT of the data as described above.
• Autocorrelation: These options measure to what extent the sound repeats itself. This is done by taking two copies of the audio, and moving one forward by one sample. The two copies are then multiplied together, and all the values added up. This is repeated for two samples difference and so on, up to the number of samples in the size option. This gives a small result if the waveform is random (for example, noise) and a large result if it is repetitive (like a musical note). By looking at the peaks in the plot, the key frequencies present can be determined even if there is a lot of noise.
• Cepstrum:

Size

This controls how many frequency divisions are used for the spectrum, or how many samples are used for the autocorrelation. In the Spectrum, a larger number gives more accurate frequencies (narrow bands) but averages the result over a longer period of time (because more samples are needed for the calculation). In the Autocorrelation, a large size looks for repeating patterns over a larger range of time offsets, and so will detect lower frequency patterns.

Function

Selects which mathematical function is used to pre-process the data. The basic forms of the FFT and autocorrelation algorithm require infinitely long sections of audio to work on, and so take infinitely long to complete. Hence the available audio must be pre-processed in such a way that the finite length of the audio has minimum effect. The available functions are known as "windows":

• Rectangular: is the simplest - it just cuts off the given block of samples with a sharp cut, and so leaves a sharp click at each end of the data. This means the results are often poor with a lot of random frequencies in them.
• Hamming, Hanning, Bartlett: do a smooth fade in and out of the audio data, and so give cleaner, more accurate results. Can someone explain what the differences are? I've only done Hamming!
• Blackman, Blackman-Harris:
• Welch:
• Gaussian:

Axis

When using the Spectrum, the frequencies can be displayed on a linear scale (default, which gives equal width to each increment on the scale) or on a logarithmic scale.

Beat Finder...

no documentation available yet

Regular interval labels...

This places labels in a long track so as to divide it into smaller, equally sized segments. For example, you may want to break up a long file into smaller audio files for distribution on the internet. The labels can contain the name of the separate files, then File > Export Multiple... will export all the files in one process based on the label points. You can either choose the number of labels to be created, or the interval between them.

Silence Finder...

This also places labels in a long track to divide it up, but does so at areas of silence according to the level and duration of silence you specify. This is very useful to break up a long recording such as from an LP or cassette into its individual tracks. The labels can contain the name of each track, and then File > Export Multiple... will export audio files in one process corresponding to each track of the recording. If too many silences are detected, increase the silence level and duration; if too few are detected, reduce the level and duration.