MCS  FUTURESLAB ARGONNE  CHICAGO 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 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? Methods for eliminating echo –Gain control –Separation of speaker and microphone –Room treatment –Click-to-talk –Active echo cancellation

MCS  FUTURESLAB ARGONNE  CHICAGO 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.

MCS  FUTURESLAB ARGONNE  CHICAGO 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

MCS  FUTURESLAB ARGONNE  CHICAGO 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 ARGONNE  CHICAGO Audio card, type 1 Remote echo Local feedback

MCS  FUTURESLAB ARGONNE  CHICAGO Audio card, type 2 Local Feedback Remote echo

MCS  FUTURESLAB ARGONNE  CHICAGO Gentner Architecture

MCS  FUTURESLAB ARGONNE  CHICAGO 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 –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 –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 ARGONNE  CHICAGO Cabling: Custom cables Gentner to XLR Male. Speakers, MM100 Gentner to XLR Female. Microphones, MM100

MCS  FUTURESLAB ARGONNE  CHICAGO 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 –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

MCS  FUTURESLAB ARGONNE  CHICAGO Preset 3: Network only

MCS  FUTURESLAB ARGONNE  CHICAGO Preset 2: Telephone only

MCS  FUTURESLAB ARGONNE  CHICAGO Preset 1: Network / Telephone Bridge

MCS  FUTURESLAB ARGONNE  CHICAGO 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 /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

MCS  FUTURESLAB ARGONNE  CHICAGO 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

MCS  FUTURESLAB ARGONNE  CHICAGO 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 Adjust for 3000 ms delay on ports and 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

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 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 –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 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

MCS  FUTURESLAB ARGONNE  CHICAGO 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

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