Distributed Systems Department Collaboration Technologies Group

Vat Advanced Techniques

VAT

• On a Sun workstation you may need to press the "Keep Audio" button to get sound to work. On an SGI Indigo 2 sound will probably quit working if you hit "Keep audio". Also, vat audio is always going to be 8kHz but on the SGI Indigo 2 you may need to reset the audio control to 8kHz after a period of silence since the machine likes to switch to 11kHz on its own.
• On a Sun Sparc5 running Solaris 2.4 or earlier you may experience audio problems. We have seen this problem as either losing the audio device or poor quality sound. For Solaris 2.4 the patch should be 102125-02 and for SunOS 4.1.3 it is probably 101508-07 and 102161-04. If you are running SunOS 4.1.4 try patch 102387-02. If you are running 4.1.x you probably also need to patch your kernel by typing the following to increase the audio buffer size.
  $adb -k -w /vmunix/dev/mem
  $audio_4231_bsize/W 0t1200 (to patch the running kernel)
  $audio_4231_bsize?W 0t1200 (to patch kernel file on disk)
  $q
  On Solaris 2.x you can set the audio buffer size by adding the following line to your /etc/system file and then rebooting.
  set audiocs:audio_4231_bsize = 1024
• If you see red bars on your mic amplitude LEDs, your gain is too high and you are saturating. Reducing your mic gain until there are no red bars will produce much better results at the listener's end.
• The problem most people encounter right away is that vat does not work quite like a phone. If you are not careful it is easy to get feedback from your speakers to your mike. The easiest way to avoid this is to use headphones to listen to the audio so it can't feed into the mike. Unfortunately, headphones are uncomfortable and often impractical. We have determined several ways of using vat that work reasonably well if you do not have hardware echo cancellation. The vat's "Output Modes" can be pretty confusing but worth understanding.
  • Mike mutes net - If your mike is turned on then anytime your mic 'hears' anything vat will send that sound out on the network regardless of what sounds are coming in from the network.
  • Net mutes mike - anything coming in from the network (remote users) will mute your mike and be played on your audio device.
  • Full duplex - provides a minimal level of software echo cancellation but this mode does not work well.
  The easiest way to use vat (without headphones) is to turn on "Mike mutes net" and hold down the right mouse button when you are speaking. This works like a walkie-talkie and I will refer to it as push-to-talk mode. If you want to instead leave the microphone on and use hands-free mode then there are several things you need to know. The first is that any time your name in the vat window lights up then you are sending sound out to the network. If you are using the "Net mutes mike" and "Mike mutes net" modes opposite is better. The sites need to be using opposite modes or neither will ever break in on the other. If you want one end to leave the mike turned on it works best to have one site in "Net mutes mike" and all other sites in push-to-talk mode (with "Mike mutes net" as their output mode). For information on ways to run full duplex, see the items below.
• If you want to run vat in full duplex mode then you need a .vat.tcl file in your home directory (if you are already running vat when you fetch this file, restart vat to have it take affect). With the .vat.tcl file in place, vat will now have two new features. If you press the menu button there will be three new sliders under "Output mode".
  • TalkThresh - determines how much noise is required to get the microphone to key on. I find that settings 7-15 work best.
  • echoThresh - not useful
  • echoSuppressTime - determines how long after playing sound that came in from the net vat will wait before unmuting the microphone.
• If you are attempting to do hands-free communication and have the output mode set to "net mutes mike" and the remote site is in "mike mutes net", but the remote site is unable to break in then you probably have your mike gain too high. When the mike gain is set to higher than 1/4 of the way up the scale then it doesn't seem to matter what output mode you and the remote site are in vat will not let the remote site break in on you. Try reducing your mike gain to less than 1/4 of the scale and it should start allowing remote sites to break in.
• If you have external echo cancellation hardware then you need to add the line
  Vat.externalEchoCancel: true
  to your .Xresources or .Xdefaults and run xrdb 'filename' to re-source the resources file. Then restart vat and you should have an additional output mode called "Ext. Echo Cancel". Which will put you in full duplex with no software echo cancellation and should only be used in conjunction with a hardware echo cancellation device.
• Most people start vat with the -r argument so that it will use RTPv2 for its communication. Sdr will automatically supply the -r to vat when it launches it. If you are starting vat from the comand line and you don't see other sites in the session that you know have joined the same multicast session, try relaunching vat with a -r.

Please also visit the

Lawrence Berkeley National Laboratory Home Page.

Distributed Systems Department Home Page.

Distributed Collaboratoratories Home Page.

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