Adds a new form of SOUND command, with only one parameter.

manual.md

@@ -938,12 +938,17 @@ Graphic and Sound Statements
 
 **Adjust voice sound parameters**  
 **SOUND _voice_, _pitch_, _dist_, _vol_ / S.**  
+**SOUND _voice_**  
 **SOUND**
 
   Adjust sound parameters for _voice_
   (from 0 to 3) ot the given _pitch_,
   _distortion_ and _volume_.
 
+  If only the _voice_ parameter is
+  present, that voice is cleared so no
+  sound is produced by that voice.
+
   If no parameters are given, clears
   all voices so that no sounds are
   produced.

src/basic.syn

@@ -400,6 +400,15 @@ NEXT_VARNAME:
 POSITION:
         emit TOK_BYTE emit COLCRS EXPR "," emit TOK_DPOKE emit TOK_BYTE emit ROWCRS EXPR emit TOK_POKE
 
+# SOUND arguments, three possibilities:
+#  SOUND voice, freq, distort, vol
+#  SOUND voice
+#  SOUND
+SOUND:
+        EXPR emit TOK_USHL emit TOK_NUM word AUDF1 emit TOK_ADD "," EXPR "," EXPR_AB emit TOK_SHL8 emit TOK_ADD emit TOK_DPOKE emit TOK_NUM word AUDCTL emit TOK_0 emit TOK_POKE emit TOK_NUM word SKCTL emit TOK_BYTE emit 3 emit TOK_POKE
+        EXPR emit TOK_USHL emit TOK_NUM word AUDF1 emit TOK_ADD emit TOK_0 emit TOK_DPOKE
+        emit TOK_SOUND_OFF
+
 # Arrays
 ARRAY_WORD_ADDR:
 	emit TOK_VAR_LOAD E_VAR_ARRAY_WORD PAR_EXPR emit TOK_USHL emit TOK_ADD
@@ -540,8 +549,7 @@ PARSE_LINE_COMMAND:
         "DRawto" POSITION emit TOK_DRAWTO
         "FIllto" POSITION emit TOK_FILLTO
         "SEtcolor" EXPR emit TOK_NUM word COLOR0 emit TOK_ADD "," EXPR_AB emit TOK_POKE
-        "Sound" EXPR emit TOK_USHL emit TOK_NUM word AUDF1 emit TOK_ADD "," EXPR "," EXPR_AB emit TOK_SHL8 emit TOK_ADD emit TOK_DPOKE emit TOK_NUM word AUDCTL emit TOK_0 emit TOK_POKE emit TOK_NUM word SKCTL emit TOK_BYTE emit 3 emit TOK_POKE
-        "Sound" emit TOK_SOUND_OFF
+        "Sound" SOUND
         "DIm" DIM_VAR DIM_MORE
         "CLose" IO_CHAN emit TOK_CLOSE
         "Open" IO_CHAN_COMMA emit TOK_BYTE emit OPEN XIO_EXPR