Dynamic Processors

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Dynamic Processors
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What does a dynamic processor do?

• They make very subtle changes to a musical sound
• They inject depth, warmth and life into our mixes
  and bring out the subtle nuances of the parts.
• They alter the range in volume between the
  loudest and softest sound on a recording or
  amplified musical performance.

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There are four main types of dynamic processors

• 1) Compressors
• 2) Limiters
• 3) Gates
• 4) Expanders

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VCA (voltage control amplifier)

• Depending on the volume of sound the VCA can
  be set to bring up or down the volume of signal.
• A VCA acts like someone who constantly
  controlling the fader on a mixing board for one
  particular sound. If a sound is too loud they
  turn it down, if a sound is too soft they turn it
  up. The advantage to a VCA is that it can act
  much faster and precisely than any human being
  and it can control the volume of several sounds
  simultaneously.

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Dynamic Processors are generally patched in two
ways

• directly to the instrument
• using the channel insert on a mixing board
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COMPRESSORS LIMITERS

• Compressors and limiters are designed to turn the
  loudest part of a signal down.
• When the VCA senses that a signal is exceeding a
  certain level it acts on the signal and turns it
  down.
• A compressor is almost always used on vocals,
  bass and on instruments with wide dynamic ranges.
  

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There are three main functions that
compressor/limiters perform

• they protect against overly loud sounds that can
  overdrive electronic circuitry and cause unwanted
  distortion.
• they even out sounds in the mix that tend to
  constantly change volume.
• they increase the overall volume of the sounds
  that we want in the mix thus improving the signal
  to noise ratio.

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There are four controls that are common to all
compressors/limiters

• i) Threshold
• ii) Attack Time
• iii) Release Time
• iv) Ratio

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i) THRESHOLD

• The threshold sets the volume (db) level at
  which the compressor will begin to recognize the
  signal. Once the signal surpasses this level its
  fate is determined by the setting of the other
  three dials. Therefore only sounds above a
  certain volume level are altered.

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ii) ATTACK TIME

• The attack time controls the amount of time
  that it takes for a compressor to turn down a
  signal once it passes over the threshold. An
  attack time that is set too fast will turn down
  the transients causing certain important elements
  of the sound to be lost. One that is too slow
  will end up allowing unwanted sounds through.

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Attack time settings

• On a vocal track we usually adjust the attack
  time in order to make it high enough that the Ss
  and Ts are heard but low enough that they are
  not exaggerated.
• On a good compressor/limiter attack times can be
  set anywhere between 100 microseconds and 20
  milliseconds.

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iii) RELEASE TIME

• The release time sets the amount of time it
  takes for the compressor to let go (or turn the
  signal back up) once it falls below the
  threshold. Release times can vary anywhere
  between 5/100 of a second to as slow as two or
  three seconds. Longer release times of one
  second or more tend to produce the smoothest and
  most natural results. This varies depending on
  the tempo of the music.

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iv) RATIO

• The ratio determines how much that a signal is
  turned down. The ratio is the comparison between
  the amount of signal that passes over the
  threshold and the actual volume of the signal
  that will be outputted from the compressor.

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How is the dB output calculated?

• Example
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• Say that you set the compressors ratio at
  31. If a sound exceeds the threshold by
• 3 dB you will actually only hear the sound as
  being 1dB above the threshold after it is
  compressed.

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Solve the following question

• If you have a sound that is 12 dB above the
  threshold with the 31 compression how loud will
  it be outputted from the compressor?

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Answer !

• The sound will be outputted at 4db above the
  threshold.
• Most compressors have an LED or VU meter to show
  how much gain reduction is taking place.

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How are Limiters and Compressors different?

• Both perform basically the same function. The
  limiter is really just an extreme compressor. It
  can compress signals at a 1001 ratio.
• Compressors perform at ratios between 11 and
  101
• Limiters perform at ratios from 101 and 1001
  (or higher)

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EXPANDERS GATES

• These are devices that are most commonly used
  when mixing down a recording
• Although gates are frequently used by musicians
  to eliminate noise in a live situation.

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EXPANDERS

• Expanders work in a similar way to a compressor
  except they act on the signal that is below a set
  threshold is instead of above a threshold.
• Expanders are used to expand the dynamic range
  of a piece of music.
• Compressors make loud sounds softer.
• Expanders make soft sounds softer

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Upward Expanders ?

• These days sound engineers are also making
  increasing use of upward expanders (or Volume
  Maximizers) in order to take loud sounds and make
  them even louder !

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GATES

• A gate is an extreme version of an expander.
  They are used most often to eliminate noise in a
  track.
• Gates allow you to set a threshold that is
  just above the noise floor. Any sound below the
  threshold will be silent. Expanders are a little
  more effective because they allow for sounds to
  fade out a little more naturally. Gates sometimes
  cause fading out sounds to get clipped
  prematurely.

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A summary of dynamic processors

• Dynamic processors are a very powerful and
  essential tool in the studio. When used correctly
  they will lead to clean, slick, smooth and
  professional recordings. When used improperly
  they can lead to annoying ,airy and noisy
  recordings . Learning to properly use a dynamic
  proccesor is one of the most poorly understood
  yet important skills in the modern recording
  studio and live sound mixing.