Knowledge Base

Restore a Deleted Call

If you deleted a call unintentionally, do the following:

1. In the Spectrogram, drag a rectangle around the call spectrogram.
2. The call list shows a new row, with the text Manual in the Call Name cell. Double-click Manual and enter the name you require.
3. Optional: Label the call. See Labeling Calls.

If you want to restore all the deleted calls, open the Call Detection screen and click the Detect calls in this recording button to restore the deleted calls according to the current definitions. This will not restore changes that you may have applied manually, nor will it restore the calls added manually.

Problem

After creating a call definition and clicking Detect calls in this recording, UltraVox XT does not detect the calls that look like the one selected to create the call definition.

Solution

In the Call Detection screen, select the call definition and click Edit. Try the following:

• Reduce the frequency range (Freq Low - Freq High). See Keep the Frequency Range as Narrow as Possible.
• Increase Min Amplitude. Hover the mouse over the calls and take note of the amplitude values you see. Min Amplitude should stay below those values.
• If calls that are not detected show weaker signal (lower amplitude), reduce Min Amplitude by steps of for example 30 or 50, and see if this improves detection. See Increase the Min Amplitude Parameter and Get a Feel of the Amplitude in a Call.
• Reduce the Min Duration value.

  Tip: Draw a rectangle around a few calls, then in the resulting call definitions look at the Min Duration parameter and take note of the average value. When you define the true call definition, click Edit and enter half of the average value as a Min Duration. Do not forget to delete the call definitions made before.

  See Reduce Min Duration.
• Increase the Max Duration value. See Increase Max Duration.
• Reduce Min Gap. Sometimes two calls are detected as one when Min Gap is too high.
• When calls have different frequency ranges, define two call definitions instead of one.

See also: Call Definitions

I See No Vocalizations in the Spectrogram

One simple explanation is that the subject did not make vocalizations. However, it may be that the recording is so noisy that the calls do not emerge in the spectrogram.

The colors displayed in the spectrogram for one event also depend on the amplitude of the signal in the surrounding interval. The same call may appear or not (or appear less evident) if another, unwanted signal like strong noise (for example, a door being closed) or constant noise from electrical appliances occurs in the interval displayed.

To Find Out Whether There Is Constant Noise in the Signal

1. Under View, select Spectrum.
2. Look at peaks in the spectrum. If necessary, zoom in the spectrum. See Zoom In/Out.

   Examples:

   • With strong noise at 60 Hz, zoom in the left part of the spectrum.
   • In another example, after filtering at 20000 Hz, two peaks are visible at 32 kHz and 47 kHz.

See also: The Spectrogram, Factors Affecting Ultrasound Recording

Increasing Min Amplitude in a Call Definition Results in Fewer Calls Detected

This result may sound counterintuitive. One may expect to detect fewer calls after increasing the Min Amplitude parameter, that is, after applying more restrictive criteria. In fact, more calls are often detected after increasing Min Amplitude.

The reason is that when Min Amplitude is low, UltraVox XT captures large regions of the spectrogram that have amplitude higher than that value. But such large regions may not correspond to the other criteria in the call definition. For example, some regions may exceed Max Duration, and would not be considered as calls. When you increase Min Amplitude, it is more likely that smaller regions of the spectrogram will be found which correspond to all criteria in the call definition. This explains why when you increase Min Amplitude you begin to see more detected calls.

For example, suppose 50 is used for Min Amplitude. Amplitudes just above 50 are found in large regions of the spectrogram. However, such a region may not satisfy the other criteria set in the call definition — for example, it could be longer than 100 milliseconds, which conflicts with the Max Duration setting. Therefore, the call within that region is not found.

After setting a higher value of Min Amplitude and clicking Detect calls in this recording, the software finds smaller regions of the spectrogram that are above that value. This time two regions are found that match the other settings of the call definition, and therefore two calls are detected.

The third, slightly longer call is not yet found because it conflicts with the Max Duration setting. It is detected after increasing Max Duration to for example 200 ms and clicking Detect calls in this recording.

See also: The Spectrogram

Problem

In the Spectrogram, vocalizations are visible that were not detected. Further optimization of the call definition did not help.

Solution

You can add a call manually.

1. Open the Call Labeling screen (Analysis > Call Labeling).
2. Draw a rectangle around the spectrogram of the call that was missed.
3. In the detected calls list, a new row appears. Double-click the Call Name cell for that row, and change its name from Manual to the one you require.

See also: Add a Call Manually

Problem

You applied a call definition and detected most calls. However, some calls that look very prominent are not detected.

Solution

In some cases, noise at the end of a call increases the time that the signal is above the Min Amplitude threshold, pushing it above the Max Duration threshold. In such cases UltraVox XT does not detect the call because the signal appears too long to match the criteria of the call definition.

You can solve this issue in two ways:

• Increase the Min Amplitude threshold, but check that the other calls are still detected.
• Increase the Max Duration threshold. If necessary, reduce the call duration in the Call Labeling screen. See Adjust Frequency and Time Boundaries in a Call.

Problem

The spectrogram shows constant, narrow-band noise (for example, at about 70 kHz). Constant noise could be due to an electronic device near the microphone, or to the microphone being defective.

Note: Cables and electric/electronic devices produce ultrasound. Voltage changes may occur, resulting in a change in noise levels during recording, which is also difficult to deal with. Isolate all cables and devices as much as possible.

Source: UltraVox XT 4 - Calls, Noldus Information Technology