Microphones, Speakers and Echo Cancellation

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The Musical VideoconferenceAudio
Qualityvs.Echo Cancellation

• Dr. Brian K. Shepard
• Coordinator of Music Technology Programs
• University of Oklahoma School of Music

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Microphone Types

• Dynamic - rugged, warm sounding, requires higher
  sound levels
• Ribbon - rather fragile, warm sounding, works
  with fairly low sound levels
• Condenser - fairly sturdy, bright and crisp
  sounding (accurate), will work with extremely low
  sound levels

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MicrophonePolar Patterns
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Omnidirectional Microphone
Diaphragm
The Omnidirectional Microphone hears in a 360º
sphere around the diaphragm.
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Figure-8 Microphone
The Figure-8 or Bidirectional Microphone hears
in front of and behind the diaphragm.
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Cardioid Microphone
The Cardioid Pattern Microphone hears
predominantly in front of the diaphragm
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Supercardioid Microphone
The Supercardioid Pattern Microphone hears mostly
in front of the diaphragm, but has a small rear
pickup lobe.
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Hypercardioid Microphone
The Hypercardioid Pattern Microphone hears mostly
in front of the diaphragm, but with a larger rear
lobe and very little side pickup.
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Boundary Microphone
Because the Boundary Microphone is placed on a
flat surface, it hears above and beside the
diaphragm in a half-spherical pattern.
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PhysicalEcho-Cancellation
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Physical Echo-Cancellation
Speakers positioned behind, and off-axis to the
Microphones
Dynamic, Cardioid Pattern Microphones placed
close to the performer
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ElectronicGadgets
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Echo-CancellationModules
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Using Compression to DuckSpeaker Levels

• Insert a Sidechain Compressor on Speaker
  Channels
• Set Sidechain Key input to the signal from the
  local microphone(s)

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Using Compression to DuckSpeaker Levels (cont.)

• Threshold Set so the local persons level is
  above the threshold, while the remote level is
  below.
• Ratio Try between 51 and 71
• Attack Try between 100 to 250 ms
• Release Try between 500 to 1000 ms
• Makeup Gain Set at 0 dB

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Compressor Detail
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Using Gates or Expanders to Silence Microphones

• Insert a Gate or Expander on each Microphone
  Channel
• Gates turn off the channel, while Expanders turn
  down the channel. Thus, Expanders are usually
  more graceful than Gates.

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Using Gates or Expanders to Silence Microphones
(cont.)

• Threshold Set so that the local persons softest
  level is above the threshold.
• Ratio (Expander) Set below 11, Try 0.51
• Attack Try between 2 to 10 ms
• Release Try between 50 to 200 ms
• Makeup Gain (Expander) Set at 0 dB

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Gate Detail
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Expander Detail
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Using a Limiter to ControlAudio Pops and Hits

• Insert a Compressor/Limiter on Speaker Channels
• Threshold Set just above highest sound level
• Ratio Set to 201 or greater
• Attack Set as short as possible
• Makeup Gain Set to 0

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Limiter Detail
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For More Information

• Dr. Brian K. Shepard
• Coordinator of Music Technology Programs
• OU School of Music
• 500 West Boyd Street, Room 138
• Norman, OK 73019
• [phone]
• bkshepard_at_ou.edu
• music.ou.edu/internet2

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