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<TITLE>Measuring computer performance</TITLE>
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	<PARAM NAME="Keyword" VALUE="Performance benchmark">
	<PARAM NAME="Keyword" VALUE="Benchmark, performance">
	<PARAM NAME="Keyword" VALUE="CPU speed, measuring">
	<PARAM NAME="Keyword" VALUE="Computer speed, measuring">
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<H2><A NAME="benchmark"></A>Measuring computer performance</H2>

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<img src="../images/bench.png" alt="" width=276 height=358>
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<P>Many of <i>Speak Freely</i>'s <A
HREF="compresswhy.htm">compression</A> and <A
HREF="encryptwhy.htm">encryption</A> modes require substantial
amounts of computation.  In order to transmit and receive audio
in real time, without <A HREF="problemsregpauses.htm">regular
pauses</A>, your computer must be fast enough to compress
and/or encrypt audio at least as fast as it arrives from the
microphone or across the network.  The performance of machines
running Windows spans an enormous range,  and even machines
with identical processor chips may deliver dramatically
different results due to variations in cache size, memory
architecture, and the presence or absence of a floating point
unit or coprocessor.  To give an idea how well suited various
compression and encryption modes are to your own computer,
<i>Speak Freely</i> includes a built-in performance measurement
(or <I>benchmark</I>) facility, which evaluates how quickly
your computer executes the various compression and encryption
algorithms compared to the requirement for real time audio.</P>

<P>To run the benchmark, display the Help/Performance Benchmark
dialogue.  Before the benchmark has been run, all the fields
will be question marks.  To start the benchmark, press the <b>Run</b>
button.  <i>Speak Freely</i> runs each of the algorithms, both
in the mode used when transmitting and that used for reception,
for three seconds and fills in items in the table with a
percentage giving the speed at which the algorithm executed
compared to the real time audio rate.  A result of less than
100% indicates your computer cannot perform that algorithm
quickly enough to keep up with audio; any mode showing less
than 100% isn't suitable for your machine.  A measurement
substantially higher than 100% indicates the mode should be
usable.  Note, however, that for successful two-way
communication the modes you select must not only be within the
capacity of your own computer but also that of the person
you抮e talking to; if one of you has a much faster machine than
the other, you'll have to negotiate settings suitable for
both.</P>

<P>The benchmark takes about a minute to run; progress is
indicated by the filling in of fields in the table every three
seconds.  You can stop the benchmark at any time by pressing
the <b>Stop</b> button.  Since Windows is, more or less, a
multitasking system, other concurrently-running applications
may reduce the performance figures reported by the benchmark by
"stealing" compute cycles from <i>Speak Freely</i>.  To get an
idea of how <i>Speak Freely</i> will actually behave, it's best
to run the benchmark with the same background applications
you'll be running when you actually communicate using <i>Speak
Freely</i>.  (Since Windows is not noted for its real-time
response, for optimum performance it's best to run <i>Speak
Freely</i> as the only active application.)</P>

<P>When you combine various compression and encryption modes,
the performance required is often not simply the sum of the
modes selected.  Compression, for example, reduces the number
of bytes the encryption algorithms must process, and in some
cases adding the overhead of compression may enable you to use
an encryption mode your computer isn't fast enough to apply to
uncompressed data.  The performance benchmark can only give you
general guidelines; if you have a machine like the 400 MHz
Pentium II on which the sample benchmark at the start of this
section was run, any combination of modes will work fine.  If
you want to use a combination of modes that are above but
uncomfortably close to 100%, it's best to experiment with <A
HREF="loopback.htm">local loopback</A> or an <A
HREF="echo.htm">echo server</A> determine if your machine is
fast enough to squeak by.</P>

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