mcs futureslab argonne chicago access grid audio

MCS FUTURESLAB ARGONNE CHICAGO

Access Grid Audio


Goals of the audio system

• Natural high quality sound

• Full Duplex

• Hands free – microphones open

• Localization

• Spatialization

• Audio cuing


Challenges

• Audio quality

• Echo

• Making it natural

• Making the tech vanish

• Room design issues– Surface preparation

– Microphone placement

– Speaker placement


Echo

• Where does echo come from?

• Methods for eliminating echo– Gain control

– Separation of speaker and microphone

– Room treatment

– Click-to-talk

– Active echo cancellation

AudioCapture

PCGentner

Speaker

Microphone

MulticastNetwork

AcousticCoupling


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.

OutgoingAudio

Speaker

Microphone

IncomingAudio

Digital Filter

Sum


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– Midiman Delta: 4 or 6 or 10 I/O

– Single PCI slot

– Balanced audio connector (no MM100)

– Digital I/O available


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


Mic

Linein

Vol

VolInputMixer

D/AOutput

Vol

LineoutOutput

Mixer

A/DInput

Mute

Mute

Mute

Mute

Mute

Mute

Audio card, type 1

Remote echo

Local feedback


Mic

Linein

MuteVol

Vol MuteInputMixer

D/AOutput

Vol Mute

Vol MuteLineout

InputMux

A/DInput

Vol Mute c

Audio card, type 2

Local Feedback

Remote echo


Gentner Architecture

Speaker

Mic Mic Mic Mic

EC EC EC EC EC

Matrix Mixer

SpeakerAudio PC

ECReference

Gentner Echo Canceller


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


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


Audio standards

• Balanced audio– 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


Installation/Configuration Procedure

• Install hardware– Microphones

– Speakers

– Gentner

– Matchmaker MM100

– Cabling

• Gentner software setup

• Testing with rat and reflector

• Testing on the grid


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


Cabling: Custom cables

• Gentner to XLR Male. Speakers, MM100

• Gentner to XLR Female. Microphones, MM100


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


Gentner software setup

• AGDP document covers in detail

• Basic procedure– Create a site

– Set matrix routing (Presets)

– Set output levels

– Set input levels


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


Preset 3: Network only


Preset 2: Telephone only


Preset 1: Network / Telephone Bridge


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


Audio path

Speaker

Mic Mic Mic Mic

EC EC EC EC EC

Matrix Mixer

SpeakerAudio PC

ECReference



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.


Audio path

Speaker

Mic Mic Mic Mic

EC EC EC EC EC

Matrix Mixer

SpeakerAudio PC

ECReference



Testing with rat and reflector

• Local loopback test, with delay– Allows you to hear how local audio sounds remotely

– Tests both input and output path

• Start reflector on video capture machine:reflector 20000 20001

• Adjust for 3000 ms delay on ports 20000 and 20001

• Start rat on audio capture machine:rat –allowloopback ag-video/20000

• 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


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

• 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


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


Problems

• Echo– 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.


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

• No mic levels– 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


Problems

• No speaker levels– 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


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


Good luck!

• Feel free to send questions, comments, suggestions to

[email protected]

mcs futureslab argonne chicago access grid audio

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