replace in opening quotations

node123.html

@@ -75,14 +75,14 @@ idea of a comb filter.  Here we combine the input signal at four different
 time shifts (instead of two, as in the original non-recirculating comb filter), 
 each at a different positive or negative gain.  To do this, we insert the
 input signal into a delay line and tap it at three different points; the
-fourth ``tap" is the original, un-delayed signal.
+fourth "tap" is the original, un-delayed signal.
 
 <P>
 
 <DIV ALIGN="CENTER"><A NAME="fig07.30"></A><A NAME="8287"></A>
 <TABLE>
 <CAPTION ALIGN="BOTTOM"><STRONG>Figure 7.30:</STRONG>
-A ``shaker", a four-tap comb filter with randomly varying gains
+A "shaker", a four-tap comb filter with randomly varying gains
 on the taps.</CAPTION>
 <TR><TD><IMG
  WIDTH="591" HEIGHT="386" BORDER="0"