<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"> <!--Converted with LaTeX2HTML 98.1p1 release (March 2nd, 1998) originally by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds * revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan * with significant contributions from: Jens Lippmann, Marek Rouchal, Martin Wilck and others --> <HTML> <HEAD> <TITLE>Time domain analysis</TITLE> <META NAME="description" CONTENT="Time domain analysis"> <META NAME="keywords" CONTENT="vol2"> <META NAME="resource-type" CONTENT="document"> <META NAME="distribution" CONTENT="global"> <META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"> <LINK REL="STYLESHEET" HREF="vol2.css"> <LINK REL="next" HREF="node229.html"> <LINK REL="previous" HREF="node227.html"> <LINK REL="up" HREF="node222.html"> <LINK REL="next" HREF="node229.html"> </HEAD> <BODY > <!--Navigation Panel--> <A NAME="tex2html4259" HREF="node229.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html4256" HREF="node222.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html4250" HREF="node227.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html4258" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="icons.gif/contents_motif.gif"></A> <BR> <B> Next:</B> <A NAME="tex2html4260" HREF="node229.html">Presentation and inspection of</A> <B> Up:</B> <A NAME="tex2html4257" HREF="node222.html">Basic principles of time</A> <B> Previous:</B> <A NAME="tex2html4251" HREF="node227.html">Power of test statistics</A> <BR> <BR> <!--End of Navigation Panel--> <H2><A NAME="SECTION001726000000000000000"> </A><A NAME="s:itim"> </A> <BR> Time domain analysis </H2> <P> As noted above, periodic signals are best analysed in the frequency domain while stochastic signals are usually more profitably analysed in the time domain. The analysis in the time domain often involves the comparison of two different signals while in the frequency domain analyses usually concern only one signal. The expectation value of the covariance function of uncorrelated signals is zero. The expected value of the autocorrelation function (E{ACF}, Sect. <A HREF="node233.html#s:psac">12.3.2</A>) of white noise also is zero everywhere except for 1 at zero lag. The expected ACF of a stochastic signal of correlation length <I>l</I> vanishes outside a range <IMG WIDTH="54" HEIGHT="72" ALIGN="MIDDLE" BORDER="0" SRC="img478.gif" ALT="$\pm l$"> about the lags. The ACF of a deterministic function does not vanish at infinity. In particular the ACF of a function with period <I>P</I> has the same value, <I>P</I>. Signals of intermediate or mixed type with an ACF which has several maxima spaced evenly by <I>l</I> and a correlation length <IMG WIDTH="17" HEIGHT="40" ALIGN="MIDDLE" BORDER="0" SRC="img479.gif" ALT="$L\gg l$"> is called a <EM>quasiperiodic oscillation</EM>. Its power is significantly above the noise in the <!-- MATH: $1/l\pm 1/L$ --> <IMG WIDTH="52" HEIGHT="44" ALIGN="MIDDLE" BORDER="0" SRC="img480.gif" ALT="$1/l\pm 1/L$"> range of frequencies and its correlation length <I>L</I> is called the <EM>coherence length</EM>. <P> <HR> <!--Navigation Panel--> <A NAME="tex2html4259" HREF="node229.html"> <IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="icons.gif/next_motif.gif"></A> <A NAME="tex2html4256" HREF="node222.html"> <IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="icons.gif/up_motif.gif"></A> <A NAME="tex2html4250" HREF="node227.html"> <IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="icons.gif/previous_motif.gif"></A> <A NAME="tex2html4258" HREF="node1.html"> <IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="icons.gif/contents_motif.gif"></A> <BR> <B> Next:</B> <A NAME="tex2html4260" HREF="node229.html">Presentation and inspection of</A> <B> Up:</B> <A NAME="tex2html4257" HREF="node222.html">Basic principles of time</A> <B> Previous:</B> <A NAME="tex2html4251" HREF="node227.html">Power of test statistics</A> <!--End of Navigation Panel--> <ADDRESS> <I>Petra Nass</I> <BR><I>1999-06-15</I> </ADDRESS> </BODY> </HTML>