subject and no stimulus presentation. The easiest way to achieve this is to simply disconnect
the speaker. When running this test, the noise
fl
oor will typically go up by 20%. If the noise
fl
oor
increases by more than 20% the problem is likely subject related (sedatives, etc).
Diagnosing Noise Issues
Electrical noise is one of the most common problems users must address. Luckily, most
problems can be resolved easily.
Here are a few common sources of noise:
Always disconnect the preampli
fi
er from the charger and rely on the battery during recordings. No high voltage
lines should be used inside the Faraday cage. Also disconnect the charger from the wall.
See
for correct placement.
Channel 1 and Reference impedances should match at 1K-3K each.
The nearby area should be as free of high voltage noise sources as possible. Common sources are motors, fans,
refrigerators, freezers, lights, and computer monitors.
If your noise
fl
oor is higher than expected, we recommend tying the cage to a dedicated ground or connecting it to
a nearby copper pipe, if possible. Use caution if you use an electrical outlet ground. These are commonly tied to
other outlets that could introduce noise.
The charger for the Medusa4Z was left plugged in
Some subject enclosures may include interior lights or fans. These should not be used or connected to
power during ABR recordings.
Note
Ground and reference are placed incorrectly
Electrode impedances do not match
Something near the recording area is causing noise?
The subject enclosure does not have a dedicated ground
Troubleshooting | 37
