EQ & Filtering

Question 1

What is EQ in audio processing?

Answer 1

– Increases or decreases the volume of different frequency ranges.
– Can be used creatively or correctively.

Question 2

Give examples of corrective EQ.

Answer 2

– Removing snare drum ring, unwanted room resonance, bass spill on vocals, rumble or hum.

Question 3

How does a filter differ from an EQ?

Answer 3

– A filter performs one specific frequency change (passes some frequencies, cuts others).
– EQ can adjust multiple frequency bands simultaneously.

Question 4

What is cutoff frequency?

Answer 4

– The frequency at which a filter begins to reduce the signal, measured at 3 dB of gain reduction.
– Determines which frequencies pass unaffected and which are removed.

Question 5

What is centre frequency?

Answer 5

– The frequency around which a band-pass filter allows frequencies through or a parametric EQ boosts/cuts.

Question 6

What is resonance?

Answer 6

– Narrow boost of frequencies around the cutoff.
– Can create a “whistly” sound or self-oscillation if overused.

Question 7

What does Q represent?

Answer 7

– Combination of resonance and bandwidth.
– High Q = narrow filter, low Q = wide filter.

Question 8

What is filter slope?

Answer 8

– Determines how sharply a filter attenuates at the cutoff frequency, measured in dB/octave.
– Indicated on filters as LP12, LP24 (type and slope).

Question 9

What is a low-pass filter (LPF)?

Answer 9

– Reduces frequencies above the cutoff, allows frequencies below to pass.
– Used to reduce hiss or remove high-frequency noise.

Question 10

What is a high-pass filter (HPF)?

Answer 10

– Reduces frequencies below the cutoff, allows frequencies above to pass.
– Used as rumble filters, typically set between 80–150 Hz.

Question 11

What is a band-pass filter?

Answer 11

– Combination of LPF and HPF.
– Allows frequencies around a centre frequency to pass.
– Used in wah-wah pedals or telephone effects.

Question 12

What is parametric EQ (band EQ)?

Answer 12

– Allows control over gain (boost/cut), centre frequency, and Q.

Question 13

What is semi-parametric EQ?

Answer 13

– Q is fixed; only centre frequency can be adjusted for cut or boost.

Question 14

What is shelving EQ?

Answer 14

– Boosts or cuts frequencies beyond a cutoff evenly until the end of the spectrum.
– Low shelf: boosts low end (kick/bass).
– High shelf: boosts high end (drum overheads, clarity).

Question 15

How was EQ initially used in studios?

Answer 15

– Corrective: compensate for mic issues, frequency response of rooms, or recording media.

Question 16

How did EQ become creative?

Answer 16

– 1950s: engineers used it to shape recordings.
– 1960s: enhanced low frequencies, e.g., electric bass.
– 1970s: consoles (SSL, Neve) with built-in EQ allowed precise frequency shaping.

Question 17

How were filters used in early synthesizers?

Answer 17

– Manipulate timbre in real-time, creating sounds by cutting or boosting frequencies.

Question 18

How were filters creatively used on guitar?

Answer 18

– Wah-wah pedals in the 1970s swept a band-pass filter for expressive tonal effects.

Question 19

How did digital recording impact EQ usage?

Answer 19

– Improved HF response; EQ could increase brightness without adding hiss.

Question 20

What is the significance of the TB-303 in the 1990s?

Answer 20

– Used resonant filters to create iconic acid house basslines.

Question 21

How do DJs use filters?

Answer 21

– To add build-ups, breakdowns, or transitions in real-time using turntables, CDs, or laptops.

Question 22

How did CDs affect EQ practices?

Answer 22

– Better high-frequency playback allowed engineers to brighten mixes and instruments without introducing noise.

Question 23

What role do DAWs and EQ plugins play today?

Answer 23

– Editing convenience, flexibility, automation.
– Can encourage overuse or “fix it in the mix” attitudes.

Question 24

What modern EQ techniques or plugins are available?

Answer 24

– Auto-filters, dynamic EQ, resonance suppressors, multiband EQ.
– Compare master EQ/frequency response with reference tracks.

Question 25

What is the practical effect of EQ on perception?

Answer 25

– Frequency response affects perception of distance (brighter = closer, muffled = further). – Enhances clarity, punch, or warmth of instruments and mixes.

Question 26

How are filter types labelled?

Answer 26

– Two letters + number: LPF = low-pass, HPF = high-pass; number = slope severity (e.g., LP12 = 12 dB/oct).

Question 27

How does resonance affect sound?

Answer 27

– Emphasizes frequencies around cutoff. – High resonance can create self-oscillation (sine wave at cutoff).

Question 28

How does slope affect a filter?

Answer 28

– Steeper slope = stronger attenuation beyond cutoff. – Helps remove unwanted frequencies without affecting nearby ranges.

Question 29

What are common uses of low/high shelf EQ?

Answer 29

– Low shelf: kick/bass enhancement. – High shelf: drum overhead clarity, mix brightness.

Question 30

How can EQ be both corrective and creative?

Answer 30

– Corrective: remove rumble, resonance, spill. – Creative: shape timbre, create effects, emphasize musical elements.

Question 31

Give a practical example of band-pass filter use.

Answer 31

– Telephone effect on vocals or electronic instruments. – Wah-wah pedal sweeping frequencies in guitar solos.

Question 32

Why is Q important in parametric EQ?

Answer 32

– Controls bandwidth of boost/cut around centre frequency. – High Q = precise/narrow; Low Q = broad/wide.

Question 33

Historical impact of EQ and filtering

Answer 33

– 1950s: creative shaping in studios. – 1960s: enhanced bass and instrument clarity. – 1970s: SSL/Neve consoles with built-in EQ for precise control. – Synthesizers and guitar pedals used filtering for real-time sound design.

Question 34

Modern considerations in EQ/filtering

Answer 34

– Overuse can overemphasize or restrict frequency ranges. – Comparison with reference tracks ensures balanced frequency response. – Dynamic EQ and auto-filters allow frequency-dependent gain control over time.

Question 35

What is a graphic EQ?

Answer 35

– A type of EQ with multiple fixed frequency bands, each controlled by a slider or fader. – Each band can be boosted or cut independently. – Named “graphic” because the slider positions visually represent the EQ curve.

Question 36

How does a graphic EQ differ from a parametric EQ?

Answer 36

– Graphic EQ: fixed centre frequencies, Q values are pre-set, easier to use for quick adjustments. – Parametric EQ: adjustable centre frequency, Q, and gain, offering precise control.

Question 37

What are common uses of a graphic EQ?

Answer 37

– Live sound: quickly shape overall tonal balance of a PA system. – Correct room resonances or feedback. – DJing: adjust frequency content during performance.

Question 38

Practical advantage of a graphic EQ in live sound

Answer 38

– Immediate visual representation of frequency boosts/cuts. – Easier for non-technical users to balance sound quickly.

Question 39

Limitation of a graphic EQ compared to parametric EQ

Answer 39

– Fixed centre frequencies and Q make it less precise for surgical corrective EQ. – Not ideal for detailed studio mixing where precise control is required.

Question 40

How are graphic EQ bands typically spaced?

Answer 40

– Usually 1/3 octave intervals (common in live sound). – Some have 1/2 octave spacing.

Question 41

Historical note on graphic EQs

Answer 41

– Became popular in the 1970s and 1980s for live sound reinforcement. – Allowed engineers to shape frequency response quickly without complex parametric controls.