📄 loopback.htm
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<H2><A NAME="loopback"></A>Local loopback</H2>
<P>Before you try contact other people or test over the network
by contacting an <A HREF="echo.htm">echo server</A>, it's a
good idea to make sure your machine's audio hardware is set up
properly. An easy way to verify this is <i>Speak Freely</i>'s local
loopback facility, which allows you to open a connection to
your own machine that does not go over the network. Sound you
transmit is stored in memory, then replayed shortly after you
end the transmission. You can evaluate different <A
HREF="compresswhy.htm">compression modes</A> and other options,
and set your audio input and output levels optimally for the
modes you're using.</P>
<P>To establish a local loopback connection, use the Help/Local
Loopback menu item. Once the connection window appears, try
transmitting short sequences of sound (like "Testing: one, two,
three, four."). If all is well with your audio hardware, about
a second after the end of each transmission you'll hear your
voice replayed. If you don't hear anything, make sure your
speaker is plugged into the right jack on the sound card and
that the speaker volume is turned up. If you hear only a quiet
hiss or hum, see if your microphone is plugged into the correct
jack (a common error is to plug the microphone into a "Line in"
jack designed for higher-level signals than the microphone
generates). If you've checked these things and still can't
hear anything in local loopback, try the suggestions in the
list of <A HREF="faq.htm">frequently asked questions</A> on
setting up your audio hardware.</P>
<P>Since local loopback stores audio in memory rather than
sending it over the network, the length of transmission it can
store is limited. For short test messages, this isn't usually
a problem unless your machine has extremely little free
memory. If you're using <A HREF="vox.htm">voice
activation</A>, note that local loopback does not begin replay
when silence is detected, but only when you end the
transmission. The reason for this is that even though nothing
is being sent, voice activation must still "listen" in order to
resume transmission as soon as you resume speaking. With <A
HREF="hardduplex.htm">half-duplex</A> sound hardware, this
would prevent the looped-back sound from being played. Even
with full-duplex hardware, the combination of voice activation
and loopback would lead to an endless series of echoes if sound
from the speaker triggered the microphone.</P>
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