Raising the high-frequency filter (HFF) settings leads to sharper waveforms in a sleep study. High-frequency filters are designed to attenuate slower waves and enhance higher frequency activity. By increasing these settings, you effectively allow more of the high-frequency signals to pass through the system while filtering out low-frequency noise. This results in clearer, more defined waveforms, making it easier to interpret rapid brain activity, such as that seen in REM sleep or during certain stages of wakefulness.
When the HFF settings are raised, the waveform becomes less affected by background noise and artifacts that may obscure the important features of the data. In practical terms, this adjustment might lead to a more accurate representation of brain activity, as the filtered signals will more closely reflect the actual physiological events being measured.
The other options either do not contribute to sharper waveforms or may lead to less clarity in the readings. Adjusting the gain influences the amplitude but does not inherently sharpen the waveform. Lowering the HFF, conversely, would allow more low-frequency components to pass through, potentially blurring the signal. Similarly, altering the filter settings without raising the HFF might not directly improve the sharpness of the waveforms being analyzed.