Amplitude scale

Aim

Define how you want to map the values of amplitude in the spectrogram over a range of colors.

Background information

The range of values of amplitude displayed in the spectrogram is based on the minimum and maximum values in the current interval. This means that when you visualize another interval, color are assigned based on the new amplitude range.

What you choose under Amplitude scale does not change the range on the y-axis of the spectrogram. This is by default 0 to 124776 for 250 Hz microphones, and 0 to 191656 Hz for 384 kHz microphones. For non-ultrasound microphones, the range is 0 to 22010 Hz.

Procedure

1.In the Call detection or Call labeling screen, select Spectrogram and click Settings, or right-click the spectrogram window.

2.Under Amplitude scale, choose the options that you require.

Options

Linear

The option Linear maps the values of amplitude to color values using a linear function. In the linear scale color mapping, the minimum value of amplitude is given the “minimum” color (for example white; 0), and the maximum with the “maximum” color (dark blue; 255). The intermediate colors are calculated to vary linearly in the range [0, 255].

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The linear mapping may not be optimal in the following cases:

nWhen the signal varies a lot in amplitude, because the color variability is limited by the values ranging from 0 to 255 a linear color mapping may not be able to discriminate between two events of different amplitude.

nWhen energy is concentrated in a narrow range of frequencies, there may be little variation in color within the call spectrogram, because relatively few colors are available for that narrow range. In that case some spectrogram’s details may be hidden.

Log

With the Log scale color mapping, you can represent a much wider amplitude span. However, the higher the log span, the more low amplitude (including noise) is represented with “higher” colors. The Log span determines the ratio between the maximum and minimum amplitude:

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For example when choosing a Log span of 45, we obtain

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Therefore

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Select Log when the signal has a high variation in amplitude, and using Linear does not result in visible variation in color between two different values of amplitudes.If you choose Log, select the span (minimum 30, maximum 350 dB). The higher this value, the more the sound of low amplitude is represented. As a result, noise will become more evident.

Gamma

With the Gamma scale, colors are calculated based on a power law relationship, where the exponent is called Gamma (y = xg).

The Gamma option is similar to Log, but results in smoother spectrograms. If you choose Gamma, select the span (minimum 0.8, maximum 0.10). The value 0.8 gives results similar to linear mapping. The higher the span, the more the low amplitudes are represented. As a result, noise will become more evident.

Color map

Choose which color palette you want to use.

nGrayscale. From white (minimum amplitude) to black (maximum amplitude).

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nInverted grayscale. From black (minimum) to white (maximum).

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nBlue. From white (Minimum) to dark blue (Maximum).

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nBlue/Red. From white (minimum) to blue, to yellow, to red (maximum).

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nInferno. From black (minimum) to purple, to orange, to yellow (maximum).

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Notes

nA color palette has always 256 different scale values.