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Using the bandwidth, or Q, EQ control

From: Foundations of Audio: EQ and Filters

Video: Using the bandwidth, or Q, EQ control

We now know that EQ's frequency and gain controls can be used to shape a signal's frequency content by boosting or cutting various ranges of frequencies, but what defines the range of frequencies that these boost or cuts apply to? When increasing or decreasing the gain control of an EQ, even though we select a target or center frequency to work on, rarely is that the only frequency that is affected. For example, if I choose to boost a signal by 6 dBs at 2k, the frequencies around 2k also get boosted.

Using the bandwidth, or Q, EQ control

We now know that EQ's frequency and gain controls can be used to shape a signal's frequency content by boosting or cutting various ranges of frequencies, but what defines the range of frequencies that these boost or cuts apply to? When increasing or decreasing the gain control of an EQ, even though we select a target or center frequency to work on, rarely is that the only frequency that is affected. For example, if I choose to boost a signal by 6 dBs at 2k, the frequencies around 2k also get boosted.

The range or bandwidth of frequencies around the target frequency that the EQ's gain control will affect is known as Q, short for quality. In other words, Q is a way of expressing the frequency width of a filter in relation to the center frequency of a specific filter band. A boost or cut with a narrow or higher Q value will cause the EQ to affect fewer frequencies around the target frequency, while a wider or lower Q value will affect more frequencies around the target.

Listen to this example of a 6 dB boost at 2.5k as I adjust the Q from narrow to wide. Notice that the wider Q settings are more obvious because I'm boosting a wider range of frequencies. (music playing) Traditionally, Q is often represented by this mathematical relationship.

Take the center frequency and divide by the Q value. For example, a Q of 2.0 at 1000 Hz would be 1000 divided by 2, which gives us a bandwidth of 500 Hz. This filter would span a frequency range of 500 Hz, 250 Hz below the center frequency and 250 Hz above. Different EQs use different values to measure Q, so don't be surprised if your EQ doesn't follow the traditional mathematical definition.

Generally, it's safe to assume that higher Q settings result in a narrower bandwidth and lower Q settings result in a wider bandwidth around the target frequency. And realistically that's all we need to know to shape our sound to our liking. Don't let the term quality lead you to believe that a higher Q actually makes the EQ sound better or of higher quality. It just means the band of frequencies that will be boost or cut is more narrow or refined.

Narrow Q settings are most commonly used for fine-tuning a signal's frequency content and honing in on very specific areas, or residences, like the ringing of a snare or vocal sibilance. EQs with extremely narrow Qs are often referred to as notch filters, because they can be used to notch out a very narrow range of frequencies, like an unwanted 60-cycle hum. However, be careful when applying extreme gain changes with very narrow Q settings as unmusical distortion and undesired resonance or ringing can be added to the signal very quickly.

Because frequency and pitch are directly related, large boosts with very narrow Qs can cause normally un-pitched elements like a kick or snare to take on a pitch, or pitched elements to take on a wah-wah effect. In fact, a classic wah-wah pedal is just a sweepable EQ with a large boost and narrow Q. Wide Q settings can be used for broad- brush tonal shaping and are often used in mastering applications, where disrupting the frequency balance with aggressive narrow Q filters would introduce undesired artifacts.

Another way I like to think of it is that narrower or higher Q settings can be used more for solving sound problems while wider or lower Q settings can be used more for tonal shaping tasks. Some EQs have fixed Q settings that you won't be able to control, while others have Q settings that change depending on the frequency selected or the amount of gain used. For example, on the famous Neve 1073 EQ, which has seven fixed frequencies in its mid-band, the Q increases or becomes more narrow as you switch to higher frequencies.

On the Waves Renaissance EQ the Qs are asymmetrical. A boost results in a wider Q, whereas a cut results in a more narrow Q. When possible, for general-purpose EQ tasks, erring on the side of wider Q settings rather than narrower ones should be used when shaping a signal's tone, as they tend to sound more natural. However, you always want to let your ears be your guide. Narrow Q settings can be just the signature sound you're looking for, either to get a certain instrument to pop out of the mix or tame a harsh resonant buildup.

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Foundations of Audio: EQ and Filters

36 video lessons · 12858 viewers

Brian Lee White
Author

 
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  1. 3m 28s
    1. Welcome
      1m 36s
    2. What you should know before watching this course
      35s
    3. Using the exercise files
      58s
    4. Using the "Get In the Mix" Pro Tools and Logic Pro session files
      19s
  2. 15m 46s
    1. What are frequency and amplitude?
      2m 27s
    2. Measuring frequency
      1m 48s
    3. Measuring amplitude
      1m 58s
    4. The perception of frequency and amplitude
      4m 18s
    5. Frequency and pitch
      5m 15s
  3. 36m 10s
    1. What is an equalizer?
      4m 14s
    2. Hardware and software EQ
      1m 58s
    3. Understanding frequency and gain EQ controls
      3m 41s
    4. Using the bandwidth, or Q, EQ control
      5m 35s
    5. Parametric equalizers
      2m 36s
    6. Shelving filters
      5m 11s
    7. High- and low-pass filters
      5m 42s
    8. Putting it all together with multiband EQ
      3m 43s
    9. Using graphic EQ
      3m 30s
  4. 46m 13s
    1. Creating focus
      3m 47s
    2. Get in the Mix: Using EQ to fix problems and place elements in the mix
      8m 30s
    3. Get in the Mix: Creating complementary EQ curves
      9m 7s
    4. Get in the Mix: Creative EQ with the telephone effect
      5m 30s
    5. Get in the Mix: Frequency bracketing with filters
      5m 44s
    6. Get in the Mix: Automating EQ
      6m 18s
    7. Learning to listen
      3m 10s
    8. Balancing expectations from the recording process
      4m 7s
  5. 41m 14s
    1. Get in the Mix: EQing FX returns
      4m 29s
    2. Using common vintage-modeled EQs
      5m 2s
    3. Using frequency analyzers
      3m 44s
    4. Using harmonic generators to excite frequency content
      5m 44s
    5. EQ or compression first?
      3m 3s
    6. EQ and room acoustics: Is your room lying to you?
      6m 15s
    7. Boost or cut? The relative nature of EQ and headroom
      4m 0s
    8. Building healthy EQ strategies
      8m 57s
  6. 19s
    1. What's next and EQ summary
      19s
  7. 5m 51s
    1. A session with Brian Lee White
      5m 51s

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