A subset of the original v4 patch (which will become v5 eventually)

The main operational difference is that for v4 effect onward, the 
sound name will now be *TRACK*.  This will not affect existing
effects since they use version number 3 or less.

This also provides the Nyquist effect with much more information about
the current processing:

Variable       Property    What
*AUDACITY*     VERSION     current Audacity version number

*SYSTEM-DIR*   BASE        Audacity install path
*SYSTEM-DIR*   DATA        Audacity data path
*SYSTEM-DIR*   HELP        Audacity help path
*SYSTEM-DIR*   TEMP        Audacity temp file path
*SYSTEM-DIR*   PLUGIN      Audacity search path for Nyquist plugins

*PROJECT*      RATE        current project sample rate
*PROJECT*      TRACKS      total number of tracks in the project
*PROJECT*      WAVETRACKS  number of wave tracks in the project
*PROJECT*      LABELTRACKS number of label tracks in the project
*PROJECT*      MIDITRACKS  number of midi tracks in the project
*PROJECT*      TIMETRACKS  number of time tracks in the project

*SELECTION*    START       start time of current selection
*SELECTION*    END         end time of current selection
*SELECTION*    TRACKS      number of tracks in the current selection
*SELECTION*    CHANNELS    number of channels in the current selection
*SELECTION*    LOW-HZ      low frequency from spectrogram (if available, else nil)
*SELECTION*    CENTER-HZ   center frequence (calculated) (if available, else nil)
*SELECTION*    HIGH-HZ     high frequence from spectrogram (if available, else nil)
*SELECTION*    BANDWIDTH   bandwidth in octaves (calculated) (if available, else nil)
*SELECTION*    PEAK-LEVEL  peak amplitude for the current selection

*TRACK*        INDEX       1-based index of track being processed
*TRACK*        NAME        name of track
*TRACK*        TYPE        type of track: wave, midi, label, time
*TRACK*        VIEW        track view: Waveform,  Waveform (dB), etc.
*TRACK*        CHANNELS    number of channels in the track
*TRACK*        START-TIME  start time of track
*TRACK*        END-TIME    end time of track
*TRACK*        GAIN        track gain
*TRACK*        PAN         track pan
*TRACK*        RATE        sample rate of track
*TRACK*        FORMAT      sample format: 16 (int), 24 (int), 32.0 (float)
*TRACK*        CLIPS       list of start/end times for clips for each channel

lib-src/libnyquist/nyx.c

@@ -75,6 +75,7 @@ LOCAL int                 nyx_first_time = 1;
 LOCAL LVAL                nyx_obarray;
 LOCAL FLOTYPE             nyx_warp_stretch;
 LOCAL long                nyx_input_length = 0;
+LOCAL char               *nyx_audio_name = NULL;
 
 /* Suspension node */
 typedef struct nyx_susp_struct {
@@ -454,6 +455,7 @@ void nyx_init()
       argv[0] = "nyquist";
       xlisp_main_init(1, argv);
 
+      nyx_audio_name = NULL;
       nyx_os_cb = NULL;
       nyx_output_cb = NULL;
       
@@ -505,7 +507,7 @@ void nyx_cleanup()
 
    // Make sure the sound nodes can be garbage-collected.  Sounds are EXTERN
    // nodes whose value does not get copied during a full copy of the obarray.
-   setvalue(xlenter("S"), NIL);
+   setvalue(xlenter(nyx_get_audio_name()), NIL);
 
    // Free excess memory segments - does a gc()
    freesegs();
@@ -520,6 +522,11 @@ void nyx_cleanup()
    // Reset vars
    nyx_input_length = 0;
 
+   if (nyx_audio_name) {
+      free(nyx_audio_name);
+      nyx_audio_name = NULL;
+   }
+
 #if defined(NYX_MEMORY_STATS) && NYX_MEMORY_STATS
    printf("\nnyx_cleanup\n");
    xmem();
@@ -587,6 +594,25 @@ void nyx_capture_output(nyx_output_callback callback, void *userdata)
    nyx_output_ud = userdata;
 }
 
+char *nyx_get_audio_name()
+{
+   if (!nyx_audio_name) {
+      nyx_audio_name = strdup("S");
+   }
+
+   return nyx_audio_name;
+}
+
+void nyx_set_audio_name(const char *name)
+{
+   if (nyx_audio_name) {
+      free(nyx_audio_name);
+      nyx_audio_name = NULL;
+   }
+
+   nyx_audio_name = strdup(name);
+}
+
 void nyx_set_audio_params(double rate, long len)
 {
    LVAL flo;
@@ -670,7 +696,7 @@ void nyx_set_input_audio(nyx_audio_callback callback,
       }
    }
 
-   setvalue(xlenter("S"), val);
+   setvalue(xlenter(nyx_get_audio_name()), val);
 
    xlpop();
 }
@@ -862,7 +888,7 @@ nyx_rval nyx_eval_expression(const char *expr_string)
 
    xlpop(); // unprotect expr
 
-   setvalue(xlenter("S"), NIL);
+   setvalue(xlenter(nyx_get_audio_name()), NIL);
 
    gc();
 

lib-src/libnyquist/nyx.h

@@ -61,6 +61,9 @@ extern "C"
                                    void *userdata,
                                    int num_channels,
                                    long len, double rate);
+
+   char       *nyx_get_audio_name();
+   void        nyx_set_audio_name(const char *name);
    
    nyx_rval    nyx_eval_expression(const char *expr);