replace '<A NAME=' with '<A ID='
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node76.html
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node76.html
@@ -30,57 +30,57 @@ original version by: Nikos Drakos, CBLU, University of Leeds
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<BODY >
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<!--Navigation Panel-->
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<A NAME="tex2html1683"
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<BR>
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<B> Next:</B> <A NAME="tex2html1684"
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<B> Next:</B> <A ID="tex2html1684"
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HREF="node77.html">Multiplying audio signals</A>
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<B> Up:</B> <A NAME="tex2html1678"
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<B> Up:</B> <A ID="tex2html1678"
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HREF="node75.html">Modulation</A>
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<B> Previous:</B> <A NAME="tex2html1672"
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<B> Previous:</B> <A ID="tex2html1672"
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HREF="node75.html">Modulation</A>
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<B> <A NAME="tex2html1680"
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<B> <A ID="tex2html1680"
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HREF="node4.html">Contents</A></B>
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<B> <A NAME="tex2html1682"
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<B> <A ID="tex2html1682"
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HREF="node201.html">Index</A></B>
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<BR>
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<BR>
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<!--End of Navigation Panel-->
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<H1><A NAME="SECTION00910000000000000000"></A>
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<A NAME="sect5-spectra"></A>
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<H1><A ID="SECTION00910000000000000000"></A>
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<A ID="sect5-spectra"></A>
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<BR>
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Taxonomy of spectra
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</H1>
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<P>
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Figure <A HREF="#fig05.01">5.1</A> introduces a way of visualizing the
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<A NAME="5595"></A><I>spectrum</I> of an audio signal. The spectrum describes, roughly speaking,
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<A ID="5595"></A><I>spectrum</I> of an audio signal. The spectrum describes, roughly speaking,
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how the signal's power is distributed into frequencies. (Much more precise
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definitions can be given than those that we'll develop here, but they would
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require more mathematical background.)
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<P>
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<DIV ALIGN="CENTER"><A NAME="fig05.01"></A><A NAME="5599"></A>
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<DIV ALIGN="CENTER"><A ID="fig05.01"></A><A ID="5599"></A>
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<TABLE>
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<CAPTION ALIGN="BOTTOM"><STRONG>Figure 5.1:</STRONG>
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A taxonomy of timbres. The spectral envelope describes the shape of
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@@ -95,7 +95,7 @@ frequency; if discretely, it may be harmonic or inharmonic.</CAPTION>
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<P>
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Part (a) of the figure shows the spectrum of a
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<A NAME="5602"></A><I>harmonic signal</I>,
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<A ID="5602"></A><I>harmonic signal</I>,
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which is a periodic signal whose fundamental frequency is in the range of
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perceptible pitches, roughly between 50 and 4000 Hertz.
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The Fourier series (Page <A HREF="node14.html#eq-fourierseries"><IMG ALIGN="BOTTOM" BORDER="1" ALT="[*]"
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@@ -131,7 +131,7 @@ concentrated on a discrete subset of the frequency axis (a discrete
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set consists of isolated points, only finitely many in any bounded interval).
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We call
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this a
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<A NAME="5607"></A><I>discrete</I> spectrum.
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<A ID="5607"></A><I>discrete</I> spectrum.
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Furthermore, the frequencies where the signal's power lies are in the
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<IMG
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WIDTH="75" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
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@@ -140,7 +140,7 @@ Furthermore, the frequencies where the signal's power lies are in the
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necessary for <I>all</I> of the harmonic frequencies to be present; some
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harmonics may have zero amplitude.)
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For a harmonic signal, the graph of the spectrum shows the amplitudes of the
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<A NAME="5610"></A>partials of the signals.
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<A ID="5610"></A>partials of the signals.
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Knowing the amplitudes and phases of all the partials fully determines
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the original signal.
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@@ -149,7 +149,7 @@ Part (b) of the figure shows a spectrum which is also discrete, so that the
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signal can again be considered as a sum of a series of
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partials. In this case, however, there is no fundamental frequency, i.e., no
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audible common submultiple of all the partials. This is called an
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<A NAME="5611"></A>
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<A ID="5611"></A>
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<I>inharmonic</I> signal. (The terms <IMG
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WIDTH="72" HEIGHT="14" ALIGN="BOTTOM" BORDER="0"
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SRC="img406.png"
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@@ -199,7 +199,7 @@ component of zero frequency, for which
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SRC="img4.png"
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ALT="$a$">--without dividing by two.
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(Components of zero frequency are often called
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<I>DC</I><A NAME="5614"></A>
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<I>DC</I><A ID="5614"></A>
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components; "DC" is historically an acronym for "direct current").
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These conventions for amplitudes in spectra will simplify the mathematics later
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in this chapter; a deeper reason for them will become apparent in
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@@ -209,14 +209,14 @@ Chapter <A HREF="node104.html#chapter-delay">7</A>.
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Part (c) of the figure shows a third possibility:
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the spectrum might not be concentrated into a discrete set of frequencies, but
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instead might be spread out among all possible frequencies. This can be called a
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<A NAME="5616"></A><I>continuous</I>, or
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<A NAME="5618"></A><I>noisy</I> spectrum.
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<A ID="5616"></A><I>continuous</I>, or
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<A ID="5618"></A><I>noisy</I> spectrum.
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Spectra don't necessarily fall into either the discrete or continuous categories;
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real sounds, in particular, are usually somewhere in between.
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<P>
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Each of the three parts of the figure shows a continuous curve called the
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<A NAME="5620"></A><I>spectral envelope</I>. In general, sounds don't have a single,
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<A ID="5620"></A><I>spectral envelope</I>. In general, sounds don't have a single,
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well-defined
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spectral envelope; there may be many ways to draw a smooth-looking curve
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through a spectrum. On the other hand, a spectral envelope may be specified
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@@ -258,36 +258,36 @@ chapter.
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<P>
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<HR>
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<B> Next:</B> <A NAME="tex2html1684"
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<B> Next:</B> <A ID="tex2html1684"
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HREF="node77.html">Multiplying audio signals</A>
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<B> Up:</B> <A NAME="tex2html1678"
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<B> Up:</B> <A ID="tex2html1678"
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HREF="node75.html">Modulation</A>
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<B> Previous:</B> <A NAME="tex2html1672"
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<B> Previous:</B> <A ID="tex2html1672"
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HREF="node75.html">Modulation</A>
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<B> <A NAME="tex2html1680"
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<B> <A ID="tex2html1680"
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HREF="node4.html">Contents</A></B>
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<B> <A NAME="tex2html1682"
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<B> <A ID="tex2html1682"
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HREF="node201.html">Index</A></B>
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<ADDRESS>
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