Equalization

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Equalization
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Spectral Processing Devices

• Equalizers
• Filters
• Filtering Effects
• Wah Wah Pedal, Envelope Filters

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Equalization

• Changing the amplitudes of specific frequencies
  across the audible frequency spectrum.
• Audible Frequency Spectrum
• Humans 20 Hz to 20 kHz

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Just for Fun

• Species Approximate Range (Hz) 
• human 20-23,000
• dog 67-45,000 
• cat 45-64,000 
• cow 23-35,000 
• sheep 100-30,000 
• rabbit 360-42,000 
• rat 200-76,000 
• mouse 1,000-91,000
• bat 2,000-110,000 
• beluga whale 1,000-123,000
• porpoise 75-150,000
• goldfish 20-3,000 
• chicken  125-2,000 

Source www.lsu.edu/deafness/HearingRange.html
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Equalization

• Affects audio wave shape components
• 1. Fundamental - The perceived note
• 2. Overtones - Define the timbre of the sound.

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Types of EQ curves

• Bell Curve or Peak/Dip Boost/Cuts around a
  center frequency.
• Low Shelving and High Shelving boost/cuts from a
  set frequency equally onward.
• High Pass Filter Cuts lows from a set frequency
  onward by a slope rate
• Low Pass Filter Cuts highs from a set frequency
  onward by a slope rate.

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Bell or Peak/Dip EQ Curve

• Boost/Cuts around a center frequency

Source www.harmony-central.com
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Bell or Peak/Dip EQ Curve Controls

• Gain Boost/Cut (Decibels)
• Center Frequency (Hertz) selectable
  incremental steps
• sweepable continuous control
• 3. Bandwidth (Octaves) or Q (No Units)

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Bandwidth and Q

• Measurement across points -3 dB from center
  frequency.

Source Modern Recording Techniques, Huber
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Bandwidth and Q

• Q is another way we can express bandwidth.
• QCenter Frequency (Hz) / Bandwidth (Hz)
• Inverse relationship. BW increases, Q decreases.
• 1 octave bandwidth 1.41 Q
• 2 octave bandwidth .67 Q

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Shelving EQ Curves

• Boosts/Cuts from a cutoff (turnover) frequency
  equally onward

Low Shelving Curve
High Shelving Curve
Source www.harmony-central.com
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Shelving EQ Controls

• Gain Boost/Cut (dB)
• Turnover Frequency (Hz)
• Usually no BW or slope control

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Turnover (or Cutoff ) Frequency
Note that the turnover frequency is 3 dB from
the shelf.
Source Understanding Audio, Dan Thompson
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Filter EQ Curves

• High Pass Filter (HPF) Cuts Lows
• AKA Low Frequency Roll off
• Low Pass Filter (HPF) Cuts Highs
• Band Pass Filter (BPF) Combination of HPF and
  LPF, Cuts Highs and Lows.

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Low Pass Filter

• Cuts High Frequencies
• Cutoff Freq.
• -3 dB from centerline
• SlopeRate of Cutoff

Source www.harmony-central.com
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HPF has a turnover frequency (at -3 dB) of 700
Hz. Slope 6 dB / octave
LPF has a turnover frequency of 700 Hz. Slope
12 dB / octave
Source Modern Recording Techniques, Huber
Runstein
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Filter Controls

• HPF LPF Frequency Control
• filters only cut, no gain control
• Slope usually a preset rate.
• Common Slope Rates 6 dB/octave,
• 9 dB / octave, 12 dB / octave, 18 dB / octave
• BPF Bandwidth control and Center Frequency
  control, no gain control

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EQ Bands

• Band A range of frequencies to be affected
• Band A set of controls
• How many bands? Count the gain controls.
• Note HPF, LPF, and BPF usually not classified
  as bands on analog EQ devices.
• A single curve (either peak/ dip or shelving )
  is a single band.

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Equalizer Types

• Graphic - Multiple Bands (usually 10,15,or 30)
  broken down by octave increments. Fixed
  frequency, fixed bandwidth. Variable /- gain.
• 2. Parametric - More versatile EQ
• Up to 5 bands (analog device), with variable
  frequency and gain control. Also may have
  bandwidth or Q adjustment.

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Graphic Eq

• 10-band graphic EQ
• mono channel
• Freq 1 octave ranges
• Gain /- 12 dB
• BW 1 octave

Source www.api.com
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Semi-Parametric EQ

• 4 Bands
• Hi Band Bell or Hi Shelving
• Low Band Bell or Low Shelving
• Mid Bands (2) Bell Curve
• Gain /- 12 dB
• Frequency Adjust (ranges)
• BW Preset gt Semi

Source www.api.com
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Semi vs. Fully Parametric

• Semi preset or limited (switched) bandwidth
  adjustment.
• Fully sweepable (continuous) bandwidth
  adjustment.

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Selectable vs. Sweepable Frequency Control

• Selectable Switched in increments.
  Non-continuous. Limited Options.
• Sweepable Continuous adjustment.
• Ranges (ex. 20 Hz - 1kHz)
• Full Spectrum (ex. 20 Hz - 20 kHz)

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Fully Parametric Eq

• Dual Mono Design (2 mono channels)
• 4 bands per channel
• High/Low Bands Shelving or Bell Curve
• High/Low BandsNo BW controlgtSemi

www.avalondesigns.com
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Fully Parametric Eq

• Mid Bands(2) Bell Curve
• Mid Bands have BW controlgtfully parametric
• Overall Classification Fully Parametric

www.avalondesigns.com
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Parametric Pultec EQ
Source www.manleylabs.com

• Dual Mono Design (or Stereo), Tube Design
• 3 Bands per Channel
• Parametric gt Adjustable Frequency Control
• Selectable Frequency(Non continuous control)
• Low Band Low Shelving. /- Gain
• Mid Band Bell Curve, Gain Boost only
• Mid Band BW control
• Hi Band Hi Shelving, Gain Cut Only

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Wah Wah Pedal

• Pedal Controls a Center Frequency
• Bell Curve with Gain Boost or Band pass Filter
  design

Source www.zsounds.com
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Envelope Filter
Wah Wah effect triggered by an input
voltage Sensitivity processes once a threshold
level is passed Range Sweep Frequency Range
Blend Direct / Processed mix
www.dod.com