What device automatically adjusts its amplification level in response to the strength of sound?

The correct answer is a compressor. A compressor in a hearing aid is responsible for automatically adjusting amplification levels based on the intensity of the incoming sounds. This dynamic adjustment is crucial for providing a comfortable listening experience, as it ensures that loud sounds are not overwhelming while softer sounds are amplified adequately.

When the sound input is above a certain threshold, the compressor reduces the gain to prevent discomfort. Conversely, when the sound input is softer, the compressor increases the gain to ensure those sounds can still be heard clearly. This feature allows for a more natural listening experience in varying acoustic environments.

As for the other options, Real Ear Aided Gain refers to a measurement used to evaluate the performance of hearing aids, not a device that adjusts sound levels. External feedback involves the management of sound feedback, which is different from dynamically adjusting gain. Lastly, a hearing aid controller may assist with settings or programs on a hearing aid but does not perform the automatic gain adjustments that a compressor does.