Spectrograms Preferences
From Audacity Development Manual
PRL 3Jun15: I think this page needs pictures illustrating the effects of the different choices. Certainly that would clarify the time/frequency tradeoff (which existed before), and what zero padding does, which is yet another thing. I will propose some examples at the mailing lists.
- Peter 03Jun15: I agree that more information on this would be helpful, but rather than cluttering and overburdening this page I think it would be much better if you could develop a Tutorial with illustrations on the use of Spectrograms. We could then link to that Tutorial from this page.
- PRL: A Wiki page would be easier to prepare, and more useful to users wanting static side by side comparisons, and easier to translate. How about you make a link to a stub page, I'll fill it in.
Gale 02Jun15: Zero padding factor missing
- Peter 02Jun15: Done- ToDo-2 Please review the Zero padding factor.
You can view any audio track as a Spectrogram instead of a waveform by selecting Spectrogram, Spectrogram log(f) or Pitch (EAC) view from the Audio Track Dropdown Menu. Spectrograms preferences lets you adjust some of the settings for these different types of Spectrum-based view.
Spectrograms preferences does not affect settings in the Frequency Analysis window accessed by .
- Accessed by: (on a Mac
- 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 Audio Track Dropdown Menu. Some options have no effect, or a different effect, on the Pitch (EAC) view - these will be noted in the descriptions.
Peter 02Jun15: ToDo-2 I assume that these options also apply to the spectral selection views.
- PRL 02Jun15: Correct.
FFT Window
- Window Size: The dropdown 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.
- Zero padding factor: Larger values give finer interpolation of the colors along the vertical axis, at the expense of more computation time. Does not affect the time vs. frequency resolution tradeoff. Has no effect in Pitch view.
PRL 2Jun15: I simply rewrote the above. Martyn or Roger might want to give an opinion about the wording.
Display
- Minimum Frequency: This value corresponds to the bottom of the vertical scale in the spectrogram. Frequencies below this value will not be visible. The default value of "0" here will be treated as "1" when using "Spectrogram log(f)" view mode because a logarithmic scale cannot start at zero.
Gale 18Oct14: Commenting out the below as it is not true.
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.
Gale 18Oct14: Commenting out the below as it is not true.
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 "Gain". 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.
Gale 18Oct14: Commenting out the below as it is not true.
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.
