What happens to the output of a filter at its cutoff frequency?

At the cutoff frequency of a filter, the output is typically at 70.7% of its maximum value. This characteristic applies to most standard filter designs, particularly first-order filters. At this specific frequency, the filter begins to transition from its passband to its stopband, indicating a significant point of interest in frequency response analysis.

For a low-pass filter, the cutoff frequency is where the output voltage drops to approximately 70.7% of the peak output voltage (which corresponds to a -3 dB point in power), while for a high-pass filter, it also marks a similar transition at that frequency. This relationship is crucial for understanding filter behavior in various electronic applications, such as audio processing and signal conditioning. The percentage reflects a specific power ratio and is a standard figure of merit in filter circuitry design, illustrating how significantly the filter affects signal amplitude at the transition point.