Click here to purchase the entire book in PDF format. High-pass Filter A high-pass filter is essentially exactly the same as a low-pass filter, however, it permits high frequencies to pass through while attenuating low frequencies as can be seen in Figure 6.2. Just like in the previous section, the cutoff frequency is where the output has a level of -3.01 dB but now the slope below the cutoff frequency is positive because we get louder as we increase in frequency. Just like the low-pass filter, the slope of the high-pass filter is dependent on the order of the filter and can be calculated using the equation $6.02 n$ dB/oct, where $n$ is the order of the filter. Figure 6.2: The frequency response of a first-order high pass filter with a cutoff frequency of 1 kHz. Remember as well that the slope only applies to frequencies that are at least one decade away from the cutoff frequency.