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Access Grid Audio

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

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Access Grid Audio

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  1. Access Grid Audio

  2. Goals of the audio system • Natural high quality sound • Full Duplex • Hands free – microphones open • Localization • Spatialization • Audio cuing

  3. Challenges • Audio quality • Echo • Making it natural • Making the tech vanish • Room design issues • Surface preparation • Microphone placement • Speaker placement

  4. 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

  5. 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.

  6. 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

  7. 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

  8. Audio card, type 1 Local feedback Remote echo

  9. Audio card, type 2 Local Feedback Remote echo

  10. Gentner Architecture

  11. 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

  12. 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

  13. 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

  14. Installation/Configuration Procedure • Install hardware • Microphones • Speakers • Gentner • Matchmaker MM100 • Cabling • Gentner software setup • Testing with rat and reflector • Testing on the grid

  15. 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

  16. Cabling: Custom cables • Gentner to XLR Male. Speakers, MM100 • Gentner to XLR Female. Microphones, MM100

  17. 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

  18. Gentner software setup • AGDP document covers in detail • Basic procedure • Create a site • Set matrix routing (Presets) • Set output levels • Set input levels

  19. 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

  20. Preset 3: Network only

  21. Preset 2: Telephone only

  22. Preset 1: Network / Telephone Bridge

  23. 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

  24. Audio path

  25. 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.

  26. Audio path

  27. 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

  28. 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

  29. 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

  30. 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.

  31. 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

  32. 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

  33. 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

  34. Good luck! • Feel free to send questions, comments, suggestions to ag-tech@mcs.anl.gov

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