The Musical Videoconference Audio Quality vs. Echo Cancellation Dr. Brian K. Shepard Coordinator of Music Technology Programs University of Oklahoma School of Music

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

Microphone Polar Patterns

Omnidirectional Microphone The Omnidirectional Microphone hears in a 360º sphere around the diaphragm. Diaphragm

Figure-8 Microphone The “Figure-8” or Bidirectional Microphone hears in front of and behind the diaphragm.

Cardioid Microphone The Cardioid Pattern Microphone hears predominantly in front of the diaphragm

Supercardioid Microphone The Supercardioid Pattern Microphone hears mostly in front of the diaphragm, but has a small rear pickup lobe.

Hypercardioid Microphone The Hypercardioid Pattern Microphone hears mostly in front of the diaphragm, but with a larger rear lobe and very little side pickup.

Boundary Microphone Because the Boundary Microphone is placed on a flat surface, it hears above and beside the diaphragm in a half-spherical pattern.

Physical Echo-Cancellation

Dynamic, Cardioid Pattern Microphones placed close to the performer Speakers positioned behind, and off-axis to the Microphones Non-Reflective Surface behind the Performer

Electronic Gadgets

Echo-Cancellation Modules

Using Compression to “Duck” Speaker Levels Insert a “Sidechain” Compressor on Speaker Channels Set Sidechain “Key” input to the signal from the local microphone(s)

Using Compression to “Duck” Speaker Levels (cont.) Threshold: Set so the local person’s level is above the threshold, while the remote level is below. Ratio: Try between 5:1 and 7:1 Attack: Try between 100 to 250 ms Release: Try between 500 to 1000 ms Makeup Gain: Set at 0 dB

Compressor Detail

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.

Using Gates or Expanders to Silence Microphones (cont.) Threshold: Set so that the local person’s softest level is above the threshold. Ratio (Expander): Set below 1:1, Try 0.5:1 Attack: Try between 2 to 10 ms Release: Try between 50 to 200 ms Makeup Gain (Expander): Set at 0 dB

Gate Detail

Expander Detail

Using a Limiter to Control Audio Pops and “Hits” Insert a Compressor/Limiter on Speaker Channels Threshold: Set just above highest sound level Ratio: Set to 20:1 or greater Attack: Set as short as possible Makeup Gain: Set to 0

Limiter Detail

For More Information Dr. Brian K. Shepard Coordinator of Music Technology Programs OU School of Music 500 West Boyd Street, Room 138 Norman, OK (405) music.ou.edu/internet2