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Q control on Parametric EQs
- Thread starter soong
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Dominick C.
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Who or What is Q?
In the Star Trek television shows and movies, Q is a recurring character with super powers, played by actor John de Lancie. While he may serve as a sort of equalizer in the show, after a fashion, this Q has nothing to do with audio equalizers.
In equalizers, Q is the ratio of center frequency to bandwidth, and if the center frequency is fixed, then bandwidth is inversely proportional to Q—meaning that as you raise the Q, you narrow the bandwidth. Q is by far the most useful tool a parametric EQ offers, allowing you to attenuate or boost a very narrow or wide range of frequencies within each EQ band.
A narrow bandwidth (high Q) is particularly useful for removing unpleasant tones. Let’s say the snare drum in your mix has an annoying ring. With a very narrow bandwidth, you can isolate the offending frequency (usually around 1 kHz) and remove, or reject, it. This type of narrow band-reject filter is also known as a notch filter. By notching out the offending frequency, you can remove the problem without removing the instrument from the mix.
A narrow bandwidth is also useful in boosting desirable components of an instrument’s sound, such as the attack on a drum. For instance, a kick drum resonates somewhere between 60 to 125 Hz but the attack of the kick drum is much higher, at 2 to 5 kHz. By setting a narrow bandwidth and boosting the attack a bit, you can achieve a punchier kick drum without overpowering the rest of the mix.
A broad bandwidth accentuates or attenuates a larger band of frequencies. Broad and narrow bandwidths (low and high Q, respectively) are usually used in conjunction with one another to achieve the desired effect. Let’s look at our kick drum again. We have a kick drum that has a great, big, low-end sound centered around 100 Hz and an attack hitting almost dead-on at 4 kHz. In this example, you would use a broad bandwidth in the low-frequency band, centered at 100 Hz, and a narrow bandwidth boosted at 4 kHz. In this way you are accentuating the best and downplaying everything else this particular kick drum has to offer.
From [Invalid or Expired Link Removed]
In the Star Trek television shows and movies, Q is a recurring character with super powers, played by actor John de Lancie. While he may serve as a sort of equalizer in the show, after a fashion, this Q has nothing to do with audio equalizers.
In equalizers, Q is the ratio of center frequency to bandwidth, and if the center frequency is fixed, then bandwidth is inversely proportional to Q—meaning that as you raise the Q, you narrow the bandwidth. Q is by far the most useful tool a parametric EQ offers, allowing you to attenuate or boost a very narrow or wide range of frequencies within each EQ band.
A narrow bandwidth (high Q) is particularly useful for removing unpleasant tones. Let’s say the snare drum in your mix has an annoying ring. With a very narrow bandwidth, you can isolate the offending frequency (usually around 1 kHz) and remove, or reject, it. This type of narrow band-reject filter is also known as a notch filter. By notching out the offending frequency, you can remove the problem without removing the instrument from the mix.
A narrow bandwidth is also useful in boosting desirable components of an instrument’s sound, such as the attack on a drum. For instance, a kick drum resonates somewhere between 60 to 125 Hz but the attack of the kick drum is much higher, at 2 to 5 kHz. By setting a narrow bandwidth and boosting the attack a bit, you can achieve a punchier kick drum without overpowering the rest of the mix.
A broad bandwidth accentuates or attenuates a larger band of frequencies. Broad and narrow bandwidths (low and high Q, respectively) are usually used in conjunction with one another to achieve the desired effect. Let’s look at our kick drum again. We have a kick drum that has a great, big, low-end sound centered around 100 Hz and an attack hitting almost dead-on at 4 kHz. In this example, you would use a broad bandwidth in the low-frequency band, centered at 100 Hz, and a narrow bandwidth boosted at 4 kHz. In this way you are accentuating the best and downplaying everything else this particular kick drum has to offer.
From [Invalid or Expired Link Removed]
At the risk of being totally wrong 
a good way to "feel" it is that a Q of 1 is about an octave bandwidth. A typical 1/3 octave GEQ also has each band at a Q of 1 which is why they are so broad and overlapping. A Q of 2 would be a band width of 1/2 octave, etc.
I'm presently playing through an extended low end 15" cab that drops like a rock below 2K so I use a PEQ set at a Q of 4, center frequency of 4K and gain of 12dB to EQ it Bose style . I haven't had a chance to measure the result but it sounds good to me 
- I did simulate it based upon the driver's published response curve.
a good way to "feel" it is that a Q of 1 is about an octave bandwidth. A typical 1/3 octave GEQ also has each band at a Q of 1 which is why they are so broad and overlapping. A Q of 2 would be a band width of 1/2 octave, etc.I'm presently playing through an extended low end 15" cab that drops like a rock below 2K so I use a PEQ set at a Q of 4, center frequency of 4K and gain of 12dB to EQ it Bose style
. I haven't had a chance to measure the result but it sounds good to me - I did simulate it based upon the driver's published response curve.
TL;DR answer:
a big Q is like moving one slider on a graphic EQ, it affects a narrow slice of sound.
a small Q is like grabbing a bunch of graphic EQ faders in a row and pushing them all at once.
i like howInvalid Link Removed, they call that knob "bandwidth" and mark it in octaves, so you intuitively know what it does, and it sweeps from low (narrow notch) to high (broad EQ change) without you having to think "OK, small Q number = big batch of frequencies" and vice versa.
a big Q is like moving one slider on a graphic EQ, it affects a narrow slice of sound.
a small Q is like grabbing a bunch of graphic EQ faders in a row and pushing them all at once.
i like howInvalid Link Removed, they call that knob "bandwidth" and mark it in octaves, so you intuitively know what it does, and it sweeps from low (narrow notch) to high (broad EQ change) without you having to think "OK, small Q number = big batch of frequencies" and vice versa.
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