|Overview, Installation, Setup, and Configuration|
Echo Control and the Musical VTC
By definition, a VTC requires both microphones and loudspeakers at each location. Unfortunately, having live microphones in the same room with loudspeakers often causes an audio loopback when sound coming from the remote site through the speakers gets picked up by the microphones and then transmitted back to the original source where it is heard as an echo. Even with the fastest VTC codecs available, the delay on the echo can be in the range of a half second or more. For participants in the VTC, that echo can be an extreme distraction and annoyance, making effective communication and learning nearly impossible.
Over the years, a number of echo cancellers have been developed for VTCs. These devices typically work by filtering out the upper-mid and high frequencies, where much of the echo associated with speech occurs, and by using a concept known as Acoustic Echo Cancellation. AEC compares the incoming and outgoing audio streams and looks for acoustic matches. When it detects a match, it attempts to remove that sound from the audio stream with a phase-cancellation process that temporarily removes frequencies associated with the echo. For speech purposes, these two techniques can work fairly well. Speech is often made more intelligible in electronic devices when the upper, sibilant frequencies are reduced, and since speech is primarily short bursts of sound rather than long continuous tones, it is relatively simple to look for, and find, matches in the incoming and outgoing signals.
The musical VTC, however, is a completely different type of sonic environment. When musicians evaluate the sound of a musical performance, they are evaluating much more than just whether the right notes are being played. They are listening for the tone and timbre of the instrument or voice and the way it projects in the room in which it is sounding. This type of sonic information is primarily contained in the very same frequency range the typical echo canceller eliminates. Thus, it is difficult, if not impossible, to accurately evaluate a musician's sound in a VTC using traditional echo cancellation. Secondly, since music is frequently made up of long continuous tones, echo cancellers using AEC often get "confused" by the fact that the incoming and outgoing signals are quite similar and they begin to wildly fluctuate the level and the frequency content of the audio, causing unacceptable dips and cuts in the sound for the participants.
ECHODamp takes a completely different approach to echo control. Instead of limiting frequencies, it maintains the full frequency spectrum of the audio hardware used to capture the sound. Its dynamics-based algorithm determines the source of an audio signal and uses that information to help prevent echo from being transmitted in the first place. Any echo that does enter the system is damped in a manner that avoids interference with the "desired" audio. With it's intuitive design and setup, ECHODamp allows musicians, audio engineers, and VTC specialists to easily mix their audio and control echo, creating a musical VTC environment with full audio fidelity.
Physical Echo Control
In order for any echo canceller to be truly successful, users need to follow some basic microphone and loudspeaker placement techniques. There are many different types of microphones available, but for best results, a high-quality, dynamic (voice-coil) microphone with a cardioid polar response pattern should be used. Condenser microphones are famous for their accuracy and sensitivity. Unfortunately, that sensitivity usually makes them a poor choice for the musical VTC environment as they not only do a great job of hearing the performers, they also hear the loudspeakers quite well. Although they may be usable in a "speech" VTC using an AEC system, condenser microphones usually prove unworkable in the musical VTC.* The best approach for the musical VTC is one similar to that used for live stage performances that involve amplification and loudspeakers. Dynamic microphones, with cardioid patterns, are placed relatively close to the sound source, and the monitor speakers are placed behind the microphones, in their "null" pickup area (see diagram below). For added benefit, place a bit of acoustic diffusion material behind the performer to reduce "bounce" echoes from any walls or reflective surfaces behind them. Whether you use ECHODamp or not, these simple techniques will go a long way toward reducing echo in your VTCs.
*Please note that these microphone recommendations are for the two-way VTC where interaction is needed between both sites. In the case of a one-way audio/video stream, where there is no chance of audio loopback between loudspeakers and microphones, condenser microphones will sound fantastic and are highly recommended.
Downloading and uncompress the appropriate ECHODamp installer for your computer.
Macintosh: Double-click the InstallEchoDampMac.cdr file to mount the ECHODamp installer Disk Image. Double-Click the Disk Image to open it and drag the ECHODamp folder icon on top of the Applications folder icon to copy ECHODamp to the Applications folder of your computer. If you wish to install ECHODamp in some other location, simply drag the ECHODamp folder to the desired location on your computer.
Windows: Double-click the InstallEchoDampWin.exe file to launch a standard Windows Installer. Follow the on-screen instructions. By default, ECHODamp will be installed in the Program Files directory, but you may choose an alternate location in the installer wizard.
Audio Interface Connections
ECHODamp is designed to work with any CoreAudio, MME, DirectSound, or ASIO compatible computer audio interface that has a minimum of four discrete inputs and outputs. To be usable with as many interface models as possible, ECHODamp expects the following connections:
Audio Settings and Configuration
After installing ECHODamp and configuring your hardware, launch the application and select Audio Settings... (Cmd/Ctl-A) from the Setup menu at the top of your screen. In the Audio Settings window choose your preferred CoreAudio, MME, DirectSound, or ASIO device from the Driver dropdown menu. Note: these dropdown menus will vary depending on your computer platform, your installed audio drivers, and the interface options for the audio driver you choose.
Check Your Connections and Settings
Before you connect with the remote site in a VTC, you should always perform a "Loopback Test" to confirm that all of your audio (and video) connections and settings are working properly. Most VTC codecs have the ability to loop the audio and video through the system so that you can hear your audio on your own loudspeakers and see your video on your own monitors. This will help you confirm that all the local audio/video connections are working properly. It is considered good practice to do this loopback test before connecting to the remote site.
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