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Calibrating Your Audio 

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Calibrating Audio Levels Between Videoteleconference (VTC) Participants
After confirming that all the local audio is working properly, connect to the remote site for the VTC. Before you begin the actual "program" segment of your VTC, take a few moments to calibrate the audio between both sites using the tools built into ECHODamp for this purpose. Open the Calibration Tools window by selecting Calibration Tools... (Cmd/Ctl-T) from the Setup menu. The Calibration Tools window is divided into two sections: Audio Calibration tool which allows users to ensure matching audio levels at both ends of the VTC, and Latency Detector tool which calculates the round-trip latency through the entire system including codecs, audio components, and the network.

Calibration Tools Window

Audio Levels Calibration
One of the unsettling aspects of controlling audio in a VTC is the fact that the engineer at one site can neither hear the sound nor see the audio levels at the other site. This inability to compare audio levels between sites often leads to situations where one site believes they are sending the audio signal at an appropriate level, yet the other site claims the level is either too high, or to low. The Audio Calibration tool allows both sites to adjust their input levels so that the meter readings are calibrated to the same level between the two sites. This provides a degree of certainty that both sites are receiving audio at the same level it is being sent. To calibrate audio levels, both sites must first enable audio processing. Open the Audio Calibration tool and follow these steps:

Transmit Site
Audio Calibration in Transmit mode
Audio Calibration in Transmit (Tx) mode
TONE button is pressed
  Outgoing tone turns meters yellow on Codec out channels
CODEC OUT meters just turn yellow

Receive Site
Audio Calibration in Receive mode
Audio Calibration in Receive (Rx) mode
TONE button is not pressed
  Tone from remote site arrives on Codec In channels
Adjust input trims on your interface until
channel 3 & 4 meters just turn yellow

Calculating Round-Trip Latency
In order for the 2-Channel Ducker to work properly, ECHODamp needs to know the entire round-trip latency of the VTC, including all audio and network components. The Latency Detector sends a brief—and loud—beep through the entire system and calculates the amount of time it takes for that beep to be transmitted and returned through all the componentry and network. For this tool to work properly, both sites must place a microphone approximately six inches (15cm) directly in front of their left (Ch. 1) loudspeaker (see diagram).

Latency Detector Setup

Once microphones and loudspeakers are properly positioned, enable audio processing in ECHODamp at both sites, and follow these steps:

Note: To prevent feedback, the microphone channels on the Mixer are muted during this test. Thus, you will not be able to communicate through the audio channels of the VTC. Agree on your test procedure before you begin the test and/or arrange for some sort of "back-channel" communication such as a telephone or a chat client. Once the test is complete, the audio channels on the Mixer will be restored to the state they were in when you began the test.

Transmit Site
Latency Detector ready to calculate round-trip latency       Latency Detector as it times the round-trip latency
Ready to calculate round-trip latency
Input microphone selected
Transmit Mode selected
Timer Armed
  After pressing the BEEP button
Timer button indicates "Timing"
Beep LED indicators flash
with each received beep

Latency Detector after calculating round-trip latency After the Remote Beep is received, the timer stops.
The round-trip latency is displayed in milliseconds
in the Elapsed Time window.

In this example, 688ms of Elapsed Time
minus 50ms of LATENCY OFFSET
is automatically reported to the
Sidechain Delay in the main Mixer
SideChain Delay Area of Mixer

Receive Site
Latency Detector in Receive mode

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