Equalization Filters

An audio equalizer allows you to increase or decrease the strength of an audio signal within selected frequency ranges, or bands. For example, a three-band equalizer may have a gain control for the lows, midrange, and highs, so you can change the sonic “shape” of a sound by turning up some frequencies or reducing others. In general, it is much better to subtract frequencies than to amplify them, as this eliminates the possibility of distortion.

If you find that a sound is lacking “brilliance,” or high-end frequencies, try filtering out some of the bass or midrange frequencies. The overall effect is that the high-end frequencies are stronger than the lower-range frequencies. It’s easy to go too far when amplifying some frequencies, so get in the habit of reducing frequencies first. Particular kinds of sound—men’s voices, women’s voices, tape hiss, and traffic noise—all appear at different frequencies of the audio spectrum. Equalization (EQ) filters can be used for many things, from minimizing background noise in a recording to accentuating a narrator’s voice over background music. EQ filters can also create effects like making a voice sound as though it were coming through a telephone or loudspeaker (this is because telephones and loudspeakers generally don’t reproduce the high and low frequencies, only the midrange).

Frequency Ranges and Equalization

The entire range of human hearing, from 20 Hz to 20,000 Hz, can be broken into a spectrum of frequency bands: low, midrange, and high.

Note: Different devices define these ranges differently; the following ranges are approximate.

Low Frequencies

Low frequencies range from approximately 20 Hz to 250 Hz. Audible bass frequencies start around 20 Hz, though many speakers cannot reproduce frequencies this low. This is an example of how audio meters can be deceiving, because the meters may show very high signals but the speakers are not capable of making sounds that low. The lowest frequencies are felt as well as heard and require the most power to amplify. Often, subwoofer speakers are used just to handle the low frequencies in the mix (the 0.1 channel in a 5.1-channel surround sound mix is a dedicated low-frequency effects channel).

If you are trying to increase the impact of sounds like kick drums or explosions, add gain around 30 Hz or so. Filtering out 60-80 Hz removes a lot of low-end noise and rumble from wind or microphone handling. Between 150 and 250 Hz, you can add “warmth” to the audio signal (or subtract it).

Midrange Frequencies

Midrange frequencies range from approximately 250 Hz to 4000 Hz. Humans are most sensitive to this part of the audio spectrum. Most of the frequencies that make speech intelligible are in this range. You can make audio tracks stand out more in the mix by subtly increasing the frequencies in this range. At the top of this range, around 4 kHz, is where vocal sibilance occurs. Too much sibilance can be grating, but a little bit can make the voice sound crisp and detailed. If your track has too much sibilance, try reducing the 4 kHz range.

High Frequencies

High frequencies range from approximately 4000 Hz to 20,000 Hz. The high end of the frequency spectrum adds “brightness” or “brilliance” to a mix but does not affect factors such as impact (bass) or speech intelligibility. High-end frequencies can be grating, so don’t boost these frequencies too much.

Using Equalization Filters in Final Cut Pro

The following equalization filters are included with Final Cut Pro:

  • 3 Band Equalizer

  • Band Pass Filter

  • DC Notch

  • High Pass Filter

  • High Shelf Filter

  • Low Pass Filter

  • Low Shelf Filter

  • Notch Filter

  • Parametric Equalizer

All of the Final Cut Pro EQ filters use a combination of three controls. For example, the Parametric Equalizer filter contains the following controls.

Figure. Filters tab showing controls for the Parametric Equalizer filter.
  • Frequency: This slider lets you select the audio frequency you want to boost or attenuate. The lowest available frequency varies from 10 Hz for the High Pass filter to 80 Hz for the 3 Band Equalizer. The highest available frequency for all EQ filters is 20,000 Hz.
  • Q: This slider adjusts the bandwidth of the filter resonance, whose frequency value has been set with the Frequency slider.
  • Gain: This setting controls how much you’ll be boosting or attenuating the specified frequency range.