replace in opening quotations

node11.html

@@ -92,7 +92,7 @@ A convenient logarithmic scale for pitch is simply to
 count the number of half-steps from a reference pitch--allowing fractions to
 permit us to specify pitches which don't fall on a note of the Western scale.
 The most commonly used logarithmic pitch scale is
-<A NAME="1100"></A>``MIDI pitch", in which the pitch 69 is assigned to a frequency of 440 cycles
+<A NAME="1100"></A>"MIDI pitch", in which the pitch 69 is assigned to a frequency of 440 cycles
 per second--the A above middle C.  To convert between a MIDI pitch <IMG
  WIDTH="17" HEIGHT="13" ALIGN="BOTTOM" BORDER="0"
  SRC="img111.png"
@@ -153,7 +153,7 @@ second.
 MIDI itself is an old hardware protocol which has unfortunately insinuated
 itself into a great deal of software design.  In hardware, MIDI allows only
 integer pitches between 0 and 127.  However, the underlying scale is well
-defined for any ``MIDI" number, even negative ones; for example a ``MIDI pitch"
+defined for any "MIDI" number, even negative ones; for example a "MIDI pitch"
 of -4 is a decent rate of vibrato.  The pitch scale cannot, however, describe
 frequencies less than or equal to zero cycles per second. (For a clear
 description of MIDI, its capabilities and limitations, see