Update compress2.xml

added remark on treshold

opcodes/compress2.xml

@@ -62,10 +62,10 @@ corresponds to an amplitude of 0dbfs.
   <refsect1>
     <title>Performance</title>
     <para>
-      <emphasis>kthresh</emphasis> -- sets the lowest decibel level that will be allowed through.  Normally -90 or less, but if higher the threshold will begin removing low-level signal energy such as background noise.
+      <emphasis>kthresh</emphasis> -- sets the lowest decibel level that will be allowed through. This is a threshold of a separate noise gate, normally set at -90 dB or less, but if higher the threshold will begin removing low-level signal energy such as background noise.
     </para>
     <para>
-      <emphasis>kloknee</emphasis>, <emphasis>khiknee</emphasis> -- decibel break-points denoting where compression or expansion will begin. These set the boundaries of a soft-knee curve joining the low-amplitude 1:1 line and the higher-amplitude compression ratio line.  Typical values are -52 and -30 db.   If the two breakpoints are equal, a hard-knee (angled) map will result.
+      <emphasis>kloknee</emphasis>, <emphasis>khiknee</emphasis> -- decibel break-points denoting where compression or expansion will begin. These set the boundaries of a soft-knee curve joining the low-amplitude 1:1 line and the higher-amplitude compression ratio line.  Typical values are -52 and -30 dB.   If the two breakpoints are equal, a hard-knee (angled) map will result.
     </para>
     <para>
       <emphasis>kratio</emphasis> -- ratio of compression when the signal level is above the knee. The value 2 will advance the output just one decibel for every input gain of two;  3 will advance just one in three; 20 just one in twenty, etc. Inverse ratios will cause signal expansion:  .5 gives two for one, .25 four for one, etc.  The value 1 will result in no change.