Experimental setup

Example

Home cages are placed in sound-attenuating chambers. Microphones are suspended over the home cages. Especially when not using such chambers, place the computer and monitor far from the animals because they produce ultrasound.

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Factors affecting ultrasound recording

Before carrying out the actual data acquisition, make sure to run a test since several factors may affect detection of ultrasound and therefore the final result. For example:

nFluorescent tubes.

nComputer hardware components, for example the monitor.

nLitter, such as nesting material.

Remember that all kinds of human activity produce ultrasound, and that smooth surfaces reflect ultrasound whereas “hairy” surfaces absorb it.

Be aware that the amplitude of sound being recorded is likely to vary between microphones, and at different frequencies. Keep this in mind especially when using two or more microphones at the same time. The recorded amplitude may therefore differ between microphones. Also consider that microphones are often direction-sensitive, meaning that different orientation relative to the animal introduces another source of variation in your results.

Sound-attenuating chamber

To eliminate sound interference, place both the animal and the microphone in a sound-attenuating chamber. Contact Noldus for the solutions available.

Cage materials

nPlexiglas walls of home cages reflect ultrasound and result in much background noise.

nWhenever possible, use dampening material as inner walls of the cage. This reduces reflection of ultrasound against the walls.

Cables and electronic devices

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.

Sound in the room

Make sure to do all tests in a quiet room. When noise (also audible sound) is detected with very high amplitude, the amplitude scale of the spectrogram is adjusted, resulting in ultrasound calls being 'drowned' in the signal, and therefore hardly visible in the spectrogram.

See also

nMicrophone position