What percentage of actual amplitude will be visible of a 15 Hz wave when using a high-frequency filter (HFF) setting of 15 Hz?

When setting a high-frequency filter (HFF) to 15 Hz, the behavior of the filter significantly influences how much of the actual amplitude of a 15 Hz wave can be seen on the EEG recording. In general, a high-frequency filter will significantly attenuate any frequency components above the set threshold, but it also impacts the amplitude of the frequencies at and near the cutoff.

For a 15 Hz wave with an HFF of 15 Hz, the rule of thumb is that the amplitude of a wave at the cutoff frequency is typically reduced to approximately 70% of its original amplitude. This is due to the nature of filters, where signals at the cutoff frequency lose some of their amplitude due to the transition characteristics of the filter. Therefore, when a 15 Hz wave is recorded with a high-frequency filter set at 15 Hz, approximately 70% of the original amplitude (which can be rounded to 0.7) is expected to be visible on the EEG output.

This relationship between frequency settings and visible amplitude is important for EEG technologists to understand, as it affects how they interpret the data collected during an EEG examination.