Other User documentation

The vat Menu

Audio tests

The Audio Tests buttons should not be selected during a conference.

The loopback mike button will cause input from the mike to be sent to the local speaker/jack. This might be useful for checking levels and debugging cable problems but the delay from input to output makes talking in this mode almost impossible. The three tone buttons will generate one of three reference tones through the local speaker. Level setting should generally be done with the -6dBm tone.

Priority

When running multiple vat sessions on a single machine, this can be set to determine an individual session's priority for obtaining the audio device. If a window requests the audio and the window currently holding the audio is either lower priority or hasn't used audio for a specified time, the audio holder immediately gives it up. Otherwise the request is ignored.

Output mode

These buttons control what vat will do to avoid feedback/echo from the mike to the speaker.

Mike mutes net

vat will mute your output whenever it thinks that you are talking.

Net mutes mike

vat will mute your mike whenever input from the network arrives.

Full duplex

vat will assume that feedback can't happen and do nothing avoid it. The headphone jack should be set to Full duplex mode if you have headphones plugged into it and Mike mutes net if you have an external amp and speaker plugged into it.

Automatic gain control

Adjust for input and output as necessary.

Network

This area contains a miscellaneous selection of functions and information grouped into three panels.

Playout mode

Vat has two different modes of adapting the playout delay, one more suitable for an interactive, multi-party discussion or conference and the other more suitable for listening to a speech or lecture. The switch can be made at any time and takes effect immediately. The two modes differ in how quickly they forget the delay vat introduces to adapt to transient network congestion.

Conference mode This is the default when vat starts up unless the command-line flag (-l) is set on invocation. vat attempts to minimize the delay since large delays make interactive conversations difficult. This usually results in more lost packets when the delay becomes too short handle congestion.

Lecture mode In this mode, vat attempts to minimize lost packets by reducing delays very slowly. This results in the clearest playback but interactivity may suffer.

Audio encoding

Select the required output audio format by clicking on the relevant button. It not necessary to set an input format since vat will accept any packet format it knows about. More details on available audio formats are in the vat manual page.

Other details

Dest The IP address of the conference. This may be either a unicast or a multicast address. Set at the time of invocation either through sd or a command-line.

Port The port number of the conference. Set at time of invocation.

ID

TTL This is the parameter set at invocation which determines the scope of the conference. It is VERY important to set this to an appropriate level for your conference. A full discussion of etiquette for use of the Mbone is given in the Guide to Multi-media Conferencing.

Name may be changed to announce a new session name to other participants.

Key can be used to specify an encryption key, if required to gain privacy. vat allows the audio packet streams to be DES encrypted. Details of this facility are given in the vat manual page.

Title may be entered to rename the main window.