# Presentation: 402151

## Access Grid Audio

## Goals of the audio system

- Natural high quality sound
- Full Duplex
- Hands free – microphones open
- Localization
- Spatialization
- Audio cuing

**Notes:**
Easily said: discussion with remote participants needs to be as simple as with local.

## 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

## 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.

## 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

## Audio card, type 1

## Audio card, type 2

## Gentner Architecture

## 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

## 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

## 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
- 		ag-tech@mcs.anl.gov