Transcript Optimizing Audio The Musical Videoconference for the Brian K. Shepard

Optimizing Audio
for the
The Musical Videoconference
Brian K. Shepard
Chair, Department of Music Technology
University of Oklahoma School of Music
The Three Secrets of
Audio Success
• Location
of musician(s) inside the room
• Location
of proper microphones in relation to the musician(s)
• Location
of microphones in relation to the loudspeakers
Microphone Types
• Dynamic - rugged, warm sounding, requires
higher sound levels, good echo rejection
• Ribbon - rather fragile, warm sounding, works with
fairly low sound levels, moderate echo rejection
• Condenser - fairly sturdy, bright and crisp
sounding (accurate), will work with extremely low
sound levels, poor echo rejection
Microphone
Polar Patterns
Omnidirectional Microphone
Diaphragm
The Omnidirectional Microphone hears in a 360º sphere
around the 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, a little less to the side, and a small
pickup area to the rear.
Hypercardioid Microphone
The Hypercardioid Pattern Microphone hears mostly in
front of the diaphragm, with very little side pickup and a
slightly larger pickup pattern to the rear.
Boundary Microphone
The Boundary Microphone is placed on a flat surface.
Thus, it hears above and beside the diaphragm in a
half-spherical pattern.
Physical
Echo Rejection
Physical Echo Rejection
Speakers positioned
behind, or off-axis
to the Microphones
Dynamic, Cardioid
Pattern Microphones
placed close to the
performer
Non-Reflective or Diffusive Surface behind the Performer
Electronic
Gadgets
Only after completing all the
Physical Echo Rejection
Techniques
Echo-Cancellation
Modules
Using Compression to “Duck”
Local Speaker Levels
• Helps reduce the echo at your (local) end
• Insert a “Sidechain” Compressor on Speaker
Channels
• Set Sidechain “Key” input to the signal from the local
microphone(s)
Using Compression to “Duck”
Local Speaker Levels
• Threshold: Set so the local person’s level is above
the threshold, while the remote level is below.
• Ratio: Try between 10:1 and 15:1
• Attack: Try between 100 to 250 ms
• Release: Try between 500 to 1000 ms
• Makeup Gain: Set at 0 dB
Compressor Tips
• If speakers are constantly “ducked,” raise the
threshold. Set the threshold so that when you are
speaking or playing, the speakers are “ducked,” but
when the remote end is speaking or playing, the
speakers are at full level.
• Increase the ratio to make the speakers drop lower in
level when you speak or play. If they drop too much,
lower the ratio.
• The attack time should be just shorter than the round
trip echo time (generally between 100-250 ms).
• Too short of a release time can cause the
compressor to “pump.” Keep the release time in the
500-1000 ms range.
Using Gates or Expanders to
Silence Microphones
• Helps reduce the echo at the remote end
• Insert a Gate or Expander on each Microphone
Channel
• Gates turn off the channel when the input level drops,
while Expanders turn down the channel. Thus,
Expanders are usually more graceful than Gates.
Using Gates or Expanders to
Silence Microphones
• 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 1 to 10 ms
• Release: Try around 200 ms
• Makeup Gain (Expander): Set at 0 dB
Gate and Expander Tips
• If the audio from the remote end opens the gate or
the expander, raise the threshold. Set the threshold
so that the gate or expander opens when you talk or
play, but remains closed when the remote person
talks or plays.
• Set the attack time as fast as possible so that the
beginnings of your sounds do not get clipped off.
• Set the release (or hold and release) time so that
your sounds can taper off naturally before the gate or
expander closes (usually 200 ms or so).
• If your gate has a “range” value, experiment with
settings near the midpoint. This will cause the gate
to act more like an expander by dropping the audio
level rather than cutting it completely.
General Tips for Best Results
• Do physical Echo Rejection first!
• Remember, do physical Echo Rejection first!
• Do a little compression and gating at each
end rather than a lot at just one end.
• Did I mention that you should do physical
Echo Rejection first?
Mixer and Cabling Tips
• Use a mixer that allows Auxiliary Sends to be set to
“Pre-Fader,” or has assignable Bus outputs.
• Connect your microphones to separate mixer input
channels. Assign the microphone channels to either
Auxiliary (pre-fader) outputs or to separate Bus
outputs, but not to the Master L/R mix. Connect the
Auxiliary outputs (or Bus outputs) to the audio inputs
of the codec.
• Connect your codec’s audio outputs to two additional
mixer channel inputs and assign them to the Master
L/R mix.
• Plug a Gate or Expander into each of the Microphone
channels via the “Insert” jack.
Mixer and Cabling Tips
• Plug a Compressor into each of your mixer’s Main
output channels via the “Master Insert” jack.
• Assign your Microphone channels to an additional
(separate from the ones connected to the codec)
Auxiliary output and connect that output to the
Sidechain or “Key” input of the Compressor.
• Connect your mixer’s Main outputs to your amplifier
and speakers.
• If your mixer does not have a “Master Insert” jack,
plug the Main output into the Compressor’s input and
connect the output of your Compressor to your
amplifier and speakers.
For More Information
Dr. Brian K. Shepard
Chair, Department of Music Technology
OU School of Music
500 West Boyd Street, Room 138
Norman, OK 73019
(405) 325-0429
[email protected]
music.ou.edu