Knowledge Base

Note: Microphones of the 384 kHz type are not given a unique ID. Because of that, UltraVox XT stores the gain settings based on the USB port the microphone is attached to, not the microphone itself. If you plug a microphone into a different USB port, UltraVox XT will assign the gain that was last saved for that USB port, and will show no error message. To prevent confusion, always label microphones and USB ports, so you always know which microphone goes to which port.

Gain and Signal Offset

When the gain is high, an offset may appear in the Amplitude plot, that is, the average signal is higher than zero, and the maximum values are higher than unsigned minimum values. The offset is caused by the electronics of the microphone. Therefore, increasing the gain usually results in a higher offset. However this has generally no effect on your measurements. You can reduce the offset by lowering the gain.

When the offset is significantly high, it can reduce the dynamic range, that is, the range of amplitudes that can be described by a digital system. In the case of UltraVox XT where audio is sampled with a 16 bit resolution, the signal can range from -32767 to +32768. If the offset is, for example, 2500, then the positive side of the signal can be from 2500 to +32768, that is, leaving an actual range of 30268. This limitation increases the probability that loud sound exceeds the maximum possible value, generating artifacts (see below).

Gain and Frequency Artifacts

A high gain also produces additional high frequencies, which do not correspond to vocalizations. This occurs when the signal exceeds a lower or upper limit. The result is that the waveforms are cut off flat, or "clipped". When sound is loud, clipping produces extra frequencies that you can see in the spectrogram.

When setting the microphone gain, create conditions similar to those of the actual recordings. For example, put the mouse pups at the same distance from the microphone as when you carry out the real tests.

Microphone Internal Gain

If the vocalizations do not appear in the spectrogram, it may be that they are covered by overall noise. To further reduce noise, for 250-kHz microphones, you can then adjust the microphone internal gain.

Adjust the Microphone Internal Gain

Aim

To adjust the gain of the 250-kHz microphone. Do this only when adjusting the gain in UltraVox XT does not give the expected results.

• For rough gain adjustments, adjust the microphone internal gain (see below).
• For fine-tuning the output, adjust the microphone gain in UltraVox XT.

See also Experimental Setup and Microphone Position.

Procedure (250-kHz Microphone)

1. Unscrew the microphone lid (connector side) and pull out the circuit board out of the aluminium cylinder.
2. Place the microphone at the top of the cage, pointing down to the middle of the cage.
3. Connect the microphone to the PC.
4. Start UltraVox XT, and choose Setup > Experiment Settings.
5. Click Settings for that microphone, then click the Start Monitoring button.
6. In the software, set the Gain to a low value like 20. A low value is recommended because a high software gain increases noise more than the microphone's internal gain.
7. Place the microphone over the subjects. Check the waveforms on the Amplitude plot and in the spectrogram. The vocalizations should be visualized in the spectrogram. See Eliciting Vocalizations for Test Purposes.
8. Locate the trimmer on the board. This is a small box with a tiny screw on one side.
9. Gently turn the trimmer screw: counterclockwise if the waveforms are out of scale; clockwise if the call waveforms are too narrow.
10. Test the microphone with the actual sound source. There should always be a gap between signal peaks and the minimum and maximum values of the plot.
11. When finished, click the Stop Monitoring button and then click OK.
12. Put the board back in place and close the microphone.
13. For fine tuning, adjust the Gain value in UltraVox XT.

Repeat the procedure for the other microphones.

Notes

• The Dodotronic Ultramic 250 is not officially supported. However, short tests carried out with UltraVox XT 4 on Dell 3680 desktop with Windows 11 version 24H2 did not reveal significant issues.
• For 384-kHz microphones, we recommend not to adjust the internal gain. The trimmer inside the microphone only allows changes in sensitivity significantly larger than microphone-to-microphone sensitivity variation.
• To produce ultrasound, move a key chain in front of the microphone, at a fixed distance. However, with this method you do not calibrate the microphone to the real animal's vocalizations. See Eliciting Vocalizations for Test Purposes.
• Multiple microphones need not have exactly the same optimal gain. For each microphone, try to find the gain that results in a clear spectrogram of calls.

Microphone with Sampling Frequency 384 kHz

• Type: Advanced electret
• ADC Resolution: 16 bits
• Max Sampling Frequency: 384 kHz
• Frequency Range: 10 - 160 kHz
• Interface: USB 2.0, full speed, OTG/host
• Connection: Mini-B USB
• Anti-Aliasing Filter: 8th order, 160 kHz
• Dimensions: 43 mm (1 11/16") x 114 mm (4 31/64") x 13 mm (33/64")
• Weight: 60 g

Microphone with Sampling Frequency 250 kHz

• ADC Resolution: 16 bits
• Sensor: MEMS high-sensitivity Surface Mount Wide-band Ultrasonic Acoustic Sensor
• Processor: 32 bit 80 MHz integrated microcontroller
• Digital Signal Processing: 8th order anti-aliasing low-pass filter
• Connection: Mini-B USB
• Max Sampling Frequency: 250 kHz
• Frequency Range: 0 - 125 kHz
• Dimensions: Length 130 mm (5 1/8") x Diam 20 mm (25/32")
• Weight: 50 g

Select the Microphones

Aim

To choose the microphones for recording data in the current experiment.

Important: Always plug the same microphone into the same USB port. If you purchased a PC together with UltraVox XT, microphones and USB ports are labeled. Always make sure that microphones are plugged into the USB ports with the matching labels.

Prerequisites

You have created or opened an experiment. See Create a New Experiment.

Procedure

1. Connect the microphones you want to use. Important: When using multiple microphones, always connect each microphone to the same USB port. Label the microphones in such a way that you always know which microphone is connected to which port.
2. Choose Setup > Experiment Settings.
3. Click Refresh.
4. In the Microphone column, click <Select>.
5. The Select Recording Device window lists the microphones currently detected. Choose a microphone and click OK.
6. To add more microphones, repeat steps 4-5.
7. If you wish to modify the name of the microphones, click one of the cells under Microphone Name and enter a new name, e.g. cage 1.
8. Next: Adjust the microphone gain in UltraVox XT.

Source: UltraVox XT 4 - MICS, Noldus Information Technology