What happens as a receiver’s noise reduction control level is increased?
Received signals may become distorted✓Correct answer
Received frequency may become unstable
CW signals may become severely attenuated
Received frequency may shift several kHz
Explanation
DSP noise reduction estimates which parts of the spectrum are signal and which are noise and attenuates the rest, so as the level is raised more of the wanted signal is attenuated along with the noise. The result is a hollow or watery artifact and reduced intelligibility rather than any frequency instability.