Audio Recording

One of the most common but basic questions I received in this blog is “What does a high pass filter do”? This is a technical term relating to audio mixing and if you are very knowledgeable about the definition of these filters, this can help you understand what this filter does thus can aid in helping you get a better quality mix. As some problematic and troublesome frequencies in mixing can be corrected by doing high pass filter; let’s start with its basic definition.

A high pass filter will “pass” high frequencies about a specified cut-off frequencies while attenuates “drastically” below.

Still a very technical definition? Let’s illustrate an example to make easier for you. Supposing the cut-off frequency is 40Hz, if you are using a high pass filter on your audio wave sample, it will only pass 40Hz above (e.g., 50 Hz, 100Hz, 110Hz, 500Hz, 3Khz) while below 40Hz, the filter will attenuate or cut drastically in such a way it will not have “significant” amplitude. Still confused? OK, let’s use a frequency analyzer plot to illustrate the filter graphically. A frequency analyzer is a tool that plots frequency vs. amplitude. The x-axis is frequency in Hertz while the y-axis is amplitude in decibels.

Supposing you will apply a high pass filter to this audio with cutoff set at 100Hz. Using your audio recording software high pass filter function, your new frequency analyzer plot after filtering will be:

You see that below 100 Hz is drastically “cut” while allowing above 100Hz to pass. If you will use your ear, you will notice that the bass is drastically cut off if the above filtered audio is played on your studio monitors.This is an example of what a high pass filter can do. One useful application is applying high pass filter to remove the rubble at 40Hz as below these frequencies are not in any way useful in audio so it will be removed to save the dynamics for more important frequencies.