replace in opening quotations

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@@ -184,7 +184,7 @@ an inaudibly quiet one--is about 100 dB.
 Amplitude is related in an inexact way to the perceived loudness of a sound.
 In general, two signals with the same peak or RMS amplitude won't necessarily
 have the same loudness at all.  But amplifying a signal by 3 dB, say, will
-fairly reliably make it sound about one ``step" louder.  Much has been made of
+fairly reliably make it sound about one "step" louder.  Much has been made of
 the supposedly logarithmic nature of human hearing (and other senses), which
 may partially explain why decibels are such a useful scale of 
 amplitude [<A