From Audacity Manual
You can view any audio track as a Spectrogram instead of a waveform by selecting "Spectrogram", "Spectrogram log(f)" or "Pitch (EAC)" from the Track Drop-Down Menu. Spectrograms preferences lets you adjust some of the settings for these different types of Spectrum-based view.
- Click on any of the other Preferences sections in the above image to go directly to that Preferences page.
The options in this window apply mainly to the Spectrogram and Spectrogram log(f) views in the Track Drop-Down Menu. Some options have no effect, or a different effect, on the Pitch (EAC) view - these will be noted in the descriptions.
- Window Size: The drop-down menu lets you choose the size of the Fast Fourier Transform (FFT) window which affects how much vertical (frequency) detail you see. Larger FFT window sizes give more low frequency resolution and less temporal resolution, and are slower.
- Window type: Determines precisely how the spectrogram is computed. 'Rectangular' is slightly faster than other methods, but introduces some artifacts. All methods give broadly similar results.
- Minimum Frequency: This value corresponds to the bottom of the vertical scale in the spectrogram. Frequencies below this value will not be visible. This setting has no effect on the Pitch (EAC) view. This is because Pitch (EAC) view does not display the actual audio signal, but the output from a mathematical transformation of that signal.
- Maximum Frequency: This value corresponds to the top of the vertical scale. The value can be set to 100 Hz or any higher value. Irrespective of the entered value, the top of the scale will never exceed half the current sample rate of the track (for example, 22050 Hz if the track rate is 44100 Hz) because any given sample rate can only carry frequencies up to half that rate. A good use of this setting is in speech recognition or pitch extraction, where you can hide the visually unimportant highest frequencies and focus on the lower frequencies. Again, this setting has no effect on the Pitch (EAC) view.
- Gain (dB): This enables you to increase / decrease the brightness of the display. For small signals where the display is mostly 'blue' (dark) you can increase this value to see brighter colours and give more detail. If the display has too much 'white', decrease this value. The default is 20dB and corresponds to a -20 dB signal at a particular frequency being displayed as 'white'. The option has no effect on the Pitch (EAC) view.
- Range (dB): Affects the range of signal sizes that will be displayed as colours. The default is 80 dB and means that you won't see anything for signals 80 dB below the value set for 'Range'. This option has no effect on the Pitch (EAC) view.
- Frequency Gain (dB/dec): A positive value here gives some extra gain to higher frequencies (above 1000 Hz), as they tend to be smaller and so can't be seen as well. You get less gain at lower frequencies as well. The default is 0 dB. Setting this option to any value other than 0 or 1 will make the Pitch (EAC) view unusable.
- Show the spectrum using grayscale colors: Shows gray shades in all three views instead of full color.