replace in opening quotations

node30.html

@@ -430,7 +430,7 @@ reciprocal <IMG
  WIDTH="28" HEIGHT="32" ALIGN="MIDDLE" BORDER="0"
  SRC="img241.png"
  ALT="$1/f$">--at least approximately, and the approximation is at least
-fairly good if the waveform ``behaves well" at its ends.
+fairly good if the waveform "behaves well" at its ends.
 (As we'll see later, the waveform can always be forced to behave at least
 reasonably well by enveloping it as in Figure <A HREF="node29.html#fig02.07">2.7</A>.)
 
@@ -449,9 +449,9 @@ curve is both compressed to the left (the frequencies all drop) and amplified
 <TABLE>
 <CAPTION ALIGN="BOTTOM"><STRONG>Figure 2.10:</STRONG>
 The Fourier series magnitudes for the waveforms shown in Figure
-<A HREF="#fig02.09">2.9</A>.  The horizontal axis is the harmonic number.  We only ``hear"
+<A HREF="#fig02.09">2.9</A>.  The horizontal axis is the harmonic number.  We only "hear"
 the coefficients for integer harmonic numbers; the continuous curves are the
-``ideal" contours.</CAPTION>
+"ideal" contours.</CAPTION>
 <TR><TD><IMG
  WIDTH="474" HEIGHT="317" BORDER="0"
  SRC="img242.png"
@@ -467,11 +467,11 @@ interpolate between each pair of consecutive points of the 100 percent duty
 cycle contour (the original one) with 99 new ones.  Already in the figure the
 50 percent duty cycle trace defines the curve with twice the resolution of
 the original one.  In the limit, as the duty cycle gets arbitrarily small, the
-spectrum is filled in more and more densely; and the limit is the ``true"
+spectrum is filled in more and more densely; and the limit is the "true"
 spectrum of the waveform.
 
 <P>
-This ``true" spectrum is only audible at suitably low duty cycles, though.  The
+This "true" spectrum is only audible at suitably low duty cycles, though.  The
 200 percent duty cycle example actually misses the peak in the ideal
 (continuous) spectrum because the peak falls below the first harmonic.  In
 general, higher duty cycles sample the ideal curve at lower resolutions.
@@ -484,11 +484,11 @@ endlessly variable waveforms from recorded samples (Section
 <A HREF="node28.html#sect2.sampling">2.2</A>), it is possible to generate all sorts of sounds.
 For example, the block diagram of Figure <A HREF="node29.html#fig02.07">2.7</A> gives us a
 way to to grab and stretch timbres from a recorded wavetable.  When the
-``frequency" parameter <IMG
+"frequency" parameter <IMG
  WIDTH="13" HEIGHT="30" ALIGN="MIDDLE" BORDER="0"
  SRC="img112.png"
  ALT="$f$"> is high enough to be audible as a pitch, the
-``size"
+"size"
 parameter <IMG
  WIDTH="10" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
  SRC="img208.png"