Transcript Spectral Processing

Equalization
Spectral Processing Devices
• Equalizers
• Filters
• Filtering Effects:
Wah Wah Pedal, Envelope Filters
Equalization
• Changing the amplitudes of specific
frequencies across the audible
frequency spectrum.
• Audible Frequency Spectrum:
Humans: 20 Hz to 20 kHz
Just for Fun
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Species
human
dog
cat
cow
sheep
rabbit
rat
mouse
bat
beluga whale
porpoise
goldfish
chicken
Approximate Range (Hz)
20-23,000
67-45,000
45-64,000
23-35,000
100-30,000
360-42,000
200-76,000
1,000-91,000
2,000-110,000
1,000-123,000
75-150,000
20-3,000
125-2,000
Source: www.lsu.edu/deafness/HearingRange.html
Equalization
Affects audio wave shape components:
1. Fundamental - The perceived note
2. Overtones - Define the timbre of the
sound.
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.
Bell or Peak/Dip EQ Curve
• Boost/Cuts around a center frequency
Source: www.harmony-central.com
Bell or Peak/Dip EQ Curve
Controls
1. Gain: Boost/Cut (Decibels)
2. Center Frequency: (Hertz):
selectable: incremental steps
sweepable:continuous control
3. Bandwidth: (Octaves) or Q (No Units)
Bandwidth and Q
• Measurement across points -3 dB from
center frequency.
Source: Modern Recording Techniques, Huber
Bandwidth and Q
• Q is another way we can express bandwidth.
• Q=Center Frequency (Hz) / Bandwidth (Hz)
• Inverse relationship. BW increases, Q decreases.
• 1 octave bandwidth = 1.41 Q
• 2 octave bandwidth = .67 Q
Shelving EQ Curves
• Boosts/Cuts from a cutoff (turnover)
frequency equally onward
Low Shelving Curve
Source: www.harmony-central.com
High Shelving Curve
Shelving EQ Controls
1. Gain: Boost/Cut (dB)
2. Turnover Frequency: (Hz)
Usually no BW or slope control
Turnover (or Cutoff )
Frequency
* Note that the turnover frequency is 3 dB from the shelf.
Source: Understanding Audio, Dan Thompson
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.
Low Pass Filter
• Cuts High
Frequencies
• Cutoff Freq.
-3 dB from
centerline
• Slope:Rate of
Cutoff
Source: www.harmony-central.com
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
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
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.
Equalizer Types
1. 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.
Graphic Eq
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Source: www.api.com
10-band graphic EQ
mono channel
Freq: 1 octave ranges
Gain: +/- 12 dB
BW = 1 octave
Semi-Parametric EQ
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Source: www.api.com
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 => Semi
Semi vs. Fully Parametric
• Semi: preset or limited (switched)
bandwidth adjustment.
• Fully: sweepable (continuous)
bandwidth adjustment.
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)
Fully Parametric Eq
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Dual Mono Design (2 mono channels)
4 bands per channel
High/Low Bands: Shelving or Bell Curve
High/Low Bands:No BW control=>Semi
www.avalondesigns.com
Fully Parametric Eq
• Mid Bands(2): Bell Curve
• Mid Bands have BW control=>fully
parametric
• Overall Classification: Fully Parametric
www.avalondesigns.com
Source: www.manleylabs.com
Parametric Pultec EQ
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Dual Mono Design (or Stereo), Tube Design
3 Bands per Channel
Parametric => 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
Wah Wah Pedal
• Pedal Controls a Center
Frequency
• Bell Curve with Gain
Boost or Band pass
Filter design
Source: www.zsounds.com
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