8.3: Spectrum Processors

Equalizers (EQ)

An equalizer (EQ) is the most common type of spectrum processor. It allows adjustment of specific frequency bands to shape the tonal balance of audio.

Types of EQ:

• Parametric EQ
  A parametric equalizer provides precise control over each frequency band. Each band typically offers three adjustable parameters:
  

  • Frequency: The center point of the band being adjusted.
    

  • Gain: The amount of boost or cut applied to that frequency.
    

  • Bandwidth (Q): Controls how wide or narrow the range of frequencies affected will be.
    

• Parametric EQs are commonly used in studios because they allow fine-tuned control over problematic or critical frequency areas.
  

• Graphic EQ
  A graphic equalizer divides the frequency spectrum into fixed bands (for example, 31 bands in a 1/3-octave EQ). Each band is controlled by a slider that boosts or cuts that frequency range. The physical or visual layout of the sliders represents the “shape” of the frequency curve — hence the name graphic.
  
  Graphic EQs are often used in live sound reinforcement for adjusting overall system tone or reducing feedback frequencies.
  

• Shelving EQ
  A shelving equalizer boosts or cuts all frequencies above or below a selected point.
  

  • High-shelf EQs affect the treble region.
    

  • Low-shelf EQs affect the bass region.
    

• Peaking EQ
  A peaking filter boosts or cuts a specific band around a central frequency, leaving other frequencies largely unaffected. This is the most typical filter used in parametric equalizers.
  

Filters

Filters are specialized EQ circuits designed to remove or isolate certain frequency ranges.
Examples include:

• High-pass filters (HPF): Remove low frequencies below a cutoff point.
  

• Low-pass filters (LPF): Remove high frequencies above a cutoff point.
  

• Band-pass filters: Allow only a specific range of frequencies through.
  

• Notch filters: Remove a very narrow band, often used to eliminate hum or resonance.
  

Filters are used in many audio applications, including crossovers, noise control, and instrument tone shaping.

Psychoacoustic Processors

A psychoacoustic processor is a type of spectrum processor that enhances perceived clarity, brightness, or presence by manipulating harmonics and phase relationships, rather than simply boosting frequencies. These devices rely on the way the human ear perceives sound rather than on actual amplitude changes.

Examples include:

• Aphex Aural Exciter: Adds synthesized harmonics to enhance detail and brightness, often used on vocals and acoustic instruments.
  

• BBE Sonic Maximizer: Alters phase and amplitude relationships to improve clarity and definition.
  

• Enhancers/Exciters: Add subtle distortion or harmonic content that makes sound appear more lively and open.
  

These processors are commonly used in mastering, broadcasting, and live performance to add “sparkle” and definition to a mix. Spectrum processors provide engineers with precise control over the tonal characteristics of sound. Processors like equalizers, filters, and psychoacoustic enhancers shape the frequency spectrum to achieve clarity, balance, and artistic expression.