About the microphone gain

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.

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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.

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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. For example:

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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.