Access Grid Audio
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Goals of the audio system
• Natural high quality sound
• Full Duplex
• Hands free – microphones open
• Localization
• Spatialization
• Audio cuing
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Challenges
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Audio quality
Echo
Making it natural
Making the tech vanish
Room design issues
– Surface preparation
– Microphone placement
– Speaker placement
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Echo
• Where does echo come from?
Speaker
Multicast
Network
Audio
Capture
PC
Acoustic
Coupling
Gentner
Microphone
• Methods for eliminating echo
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Gain control
Separation of speaker and microphone
Room treatment
Click-to-talk
Active echo cancellation
MCS ) FUTURESLAB
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Echo Canceller
• Computes estimate of echo return signal from speaker to
microphone
• Subtracts echo return estimate from microphone audio
• Echo-free audio sent to output.
Incoming
Audio
Speaker
Digital Filter
Outgoing
Audio
MCS ) FUTURESLAB
Sum
Microphone
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Audio codecs
• Currently use commodity PC audio cards
– Creative Ensoniq AudioPCI
– Cheap! $30
– Good quality
• Multiple inputs require multiple cards
– And slots
• Future: pro audio cards
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Midiman Delta: 4 or 6 or 10 I/O
Single PCI slot
Balanced audio connector (no MM100)
Digital I/O available
MCS ) FUTURESLAB
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PC audio cards
• Internal mixer
• Level adjustment for output has two controls: PCM level,
main output level
• Input has one or two controls, depending on card
• Different cards may have different mixer semantics
– Rat tries to accommodate this
• Implications
– Possible (easy) to cause local feedback with looped back line in to line
out audio path
– Possible (easy) to cause remote echo with looped back digital output to
digital input path
– Output level depends on two separate settings
MCS ) FUTURESLAB
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Audio card, type 1
Mic
Vol
Mute
A/D
Input
Local feedback
Line
in
Vol
D/A
Output
Vol
Remote echo
Mute
Input
Mixer
Mute
Mute
Mute
Output
Mixer
Line
out
Mute
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Audio card, type 2
Mic
Vol
Mute
Vol
Local Feedback
Line
in
Vol
Mute
D/A
Output
Vol
Mute
Mute
Line
out
Input
Mixer
Input
Mux
Vol
Mute
c
A/D
Input
Remote echo
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Gentner Architecture
Mic
Mic
Mic
Mic
Gentner Echo Canceller
EC
EC
EC
EC
EC
EC
Reference
Matrix Mixer
Audio PC
MCS ) FUTURESLAB
Speaker
Speaker
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Gentner features
• Echo cancellation per-input
– “Distributed echo cancellation”
– Allows more accurate echo return calculation
• Automixing
– Gates microphones off when no input detected
– Ensures very quiet audio from a site when nobody speaking
• Adaptive ambient
– Monitors ambient noise levels to only gate microphones on when
levels increase above ambient
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Gentner vs. External Mixer
• Why can’t we just plug lots of microphones into a mixer, then
plug the mixer into the Gentner?
– The distributed echo cancellation on each input has to work harder and
cannot converge quickly.
– When the microphones are gated "off" by the external mixer, the
AP800 echo canceller has nothing to train to within the room.
– There is no communication between the mixer and the AP800, so the
systems does not take advantage of the Adaptive Ambient feature.
• It may appear to work, but under stress (multiple speakers,
ambient noise) it will fail
• Gentner works best when used as designed
• Money spent on doing it right is money well spent
• Driving non-microphone inputs through an external mixer to
the Gentner is not a problem
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Audio standards
• Balanced audio
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2 wires for signal, one for ground
Differential signal
Excellent noise rejection
Professional audio gear (Gentner, Midiman audio codec)
• Unbalanced audio
– 1 wire for signal, one for ground
– Little noise rejection
– Consumer-grade audio gear (standard PC audio codec)
• Level matching
– Consumer and pro audio gear have different voltage level standards
• Matchmaker does both balanced/unbalanced and level
conversion
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Installation/Configuration Procedure
• Install hardware
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Microphones
Speakers
Gentner
Matchmaker MM100
Cabling
• Gentner software setup
• Testing with rat and reflector
• Testing on the grid
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Install hardware
• Place microphones
– Saturate space
– Unobtrusive
• Place speakers
• Install Gentner
– Rackmount if possible
• Install MM100
– Rackmount if possible
• Power connections
– Connect Gentner, MM100, speakers, Audio Capture machine to power
line filter
MCS ) FUTURESLAB
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Cabling: Custom cables
• Gentner to XLR Male. Speakers, MM100
• Gentner to XLR Female. Microphones, MM100
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Cabling
• Custom cable options
– Cut up existing XLR microphone/patch cable
• Hard to strip
• More flexible
– Build new cables from bulk cable
• Need to install XLRs
• Bulk foil-shield cable thinner, better shielding
• Good for long-run fixed installation
– Patch panel
• Terminate Gentner connectors in panel-mount XLR
• Very good option for overall neatness and organization
• Other cables
– RCA to 1/8”. PC to MM100
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Gentner software setup
• AGDP document covers in detail
• Basic procedure
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Create a site
Set matrix routing (Presets)
Set output levels
Set input levels
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Gentner presets
• Three modes for Gentner operation:
– Network only. Remote audio from Audio Capture machine, local
audio to Audio Capture machine.
– Telco only. Remote audio from Telephone, local audio to Telephone
– Network/Telco bridge. Bridges between local audio, network, and
Telephone.
• Why?
– Support for failover
– Support for telephone-only dialins
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Preset 3: Network only
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Preset 2: Telephone only
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Preset 1: Network / Telephone Bridge
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Set input levels
• For each microphone:
– Recruit a volunteer to read text at a normal speaking voice
– Adjust microphone gain for levels of roughly –10dB, peaking at 0dB
– (Crown PCC-160 input settings to 55dB coarse, -10dB fine)
• Start rat on audio machine. The address does not matter:
rat 224.1.2.3/12000
• Click transmit.
• Adjust rat input level so that normal speech stays within the
green, peaking into the yellow
• Frequent peaks into the red will result in clipping and
distortion
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Audio path
Mic
Mic
Mic
Mic
Gentner Echo Canceller
EC
EC
EC
EC
EC
EC
Reference
Matrix Mixer
Audio PC
MCS ) FUTURESLAB
Speaker
Speaker
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Set output levels
• Set all Gentner input A (Audio capture PC) and output C/D
(speaker) settings to 0dB
• Turn speakers all the way down
• Set rat output to midrange
• Start Linux mixer application (aumix or other)
• In rat, enable the test tone (Options -> Audio)
• Monitor Gentner Input A
• Adjust main volume level in mixer until Gentner levels show
0dB
• Adjust speakers for fairly loud level, slightly louder than the
loudest speech expected.
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Audio path
Mic
Mic
Mic
Mic
Gentner Echo Canceller
EC
EC
EC
EC
EC
EC
Reference
Matrix Mixer
Audio PC
MCS ) FUTURESLAB
Speaker
Speaker
ARGONNE ) CHICAGO
Testing with rat and reflector
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Local loopback test, with delay
– Allows you to hear how local audio sounds remotely
– Tests both input and output path
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Start reflector on video capture machine:
reflector 20000 20001
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Adjust for 3000 ms delay on ports 20000 and 20001
Start rat on audio capture machine:
rat –allowloopback ag-video/20000
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Click transmit
Speak normally at each mic
You should hear your voice reflected back after a delay
Adjust levels for good sound.
– Fine tune microphone balance on Gentner
– Overall adjustment with rat controls
– Aim for outgoing audio in the green and yellow range
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Testing on the grid
• Find somebody to test with
– Send mail to a colleague with a node
– Go to the Meadow on the venues mud
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Go to the Test Room
Turn on Transmit, and talk away.
Test network-only
Find a volunteer to call in, and test Telco only
Find volunteers for both network and telephone, and test
Telco bridging.
• Ripe fodder for SC Global Nanocruises
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Operations
• Muting
– Upon entry to a venue, rat
comes up muted. Click the
“talk” button to start transmission.
• Leveling
– Until a space is well shaken out, one may have to tweak the
individual microphone levels
– When well balanced, adjustments to rat mic and speaker levels
should be all that is required
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Problems
• Echo
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Echo cancellation reference set incorrectly
Echo cancellation disabled on microphones
Microphone too close to speaker
Check for loopback in PC hardware
• Levels too high
– Evidenced by rat levels into the red and clipping and distortion of
audio
– If per-mic levels in Gentner are acceptable, lower rat gains. If still a
problem, lower Gentner Input A gain.
– If mics pick up an excessive amount of room noise, decrease per-mic
gains in gentner.
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Problems
•
Levels too low
– Evidenced by rat gains at the bottom of the green
– Increase rat gain
– If rat gain is all the way up, investigate individual mic gains, and increase
Gentner Input A gain if necessary.
– If a single microphone has sharply lower than expected gain, ensure it is not
routed to the Echo Cancellation Reference output
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No mic levels
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Check cables: microphone, MM100, Audio Capture PC
Check MM100 power
For condenser microphones, check for phantom power
Check for mic input mute on Gentner
Check for output A mute on Gentner
Ensure transmit is clicked in rat
Ensure audio device in rat is set properly
Ensure input selection (mic/line) in rat is set to line
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Problems
• No speaker levels
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Check cables: speakers, MM100, Audio Capture PC
Check for Gentner Input A or Output D muting
Check speaker power and volume level
Ensure rat listen button clicked
Ensure audio device in rat is set properly
Check PC mixer master volume
• Rerun output level setting procedure
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Troubleshooting tips
• Connect headset to Gentner output
– Route individual mics or entire mix to headset
– Good for initial setup to determine quality of audio coming from
microphones
• Listen in to network transmission from another computer with
headset
– Good for monitoring important events
MCS ) FUTURESLAB
ARGONNE ) CHICAGO
Good luck!
• Feel free to send questions, comments, suggestions to
ag-tech@mcs.anl.gov
MCS ) FUTURESLAB
ARGONNE ) CHICAGO