1 files changed, 102 insertions, 0 deletions
diff --git a/nyqsrc/phasevocoder.c b/nyqsrc/phasevocoder.c
new file mode 100644
index 0000000..d446095
--- /dev/null
+++ b/nyqsrc/phasevocoder.c
@@ -0,0 +1,102 @@
+/* phasevocoder.c -- this is a stub showing how you might hook a
+   phase vocoder into Nyquist using pvshell
+ */
+
+#include "stdio.h"
+#ifndef mips
+#include "stdlib.h"
+#endif
+#include "xlisp.h"
+#include "sound.h"
+
+#include "falloc.h"
+#include "cext.h"
+#include "pvshell.h"
+
+#include "phasevocoder.h"
+
+/* use the state[] info for sample interpolation */
+#define X_VALUE state[0] /* a parameter value */
+#define F_COUNT state[1] /* counts samples of f */
+#define G_COUNT state[2] /* counts samples of g */
+#define G_PREV  state[3] /* previous value from g */
+#define G_NEXT  state[4] /* next (current?) value from g */
+/* invariant: G_NEXT is the G_COUNT'th sample of g */
+
+/* pv_fetch -- this is an example, but it doesn't really do
+ * phase vocoding. Instead, it will just multiply f, g, and x
+ *
+ * To make things a bit more interesting, we will assume g has
+ * an arbitrary sample rate with respect to f, and will interpolate.
+ * 
+ */
+long pv_fetch(pvshell_type susp, 
+              sample_block_values_type out, long *n)
+{
+    int i;
+    for (i = 0; i < *n; i++) {
+        long new_flags;
+        sample_type f;
+        double g;
+        /* NOTE: in DSP terms, this is poor code because of the
+         * division operations -- it could be made faster 
+         */
+        /* To get a value from g, first compute the time */
+        double f_time = susp->F_COUNT / susp->f->sr;
+        /* Now compute g count that is past the time */
+        double g_count = f_time * susp->g->sr;
+        while (susp->G_COUNT < g_count) {
+            PVSHELL_TEST_G(susp); /* prepare to get a sample */
+            /* ignore flags from g -- we could, if we wanted,
+             * terminate when either f or g terminated, etc.
+             */
+            susp->G_PREV = susp->G_NEXT;
+            susp->G_NEXT = PVSHELL_FETCH_G(susp);
+            susp->G_COUNT++;
+        }
+        /* now interpolate to get the value of g at f_time */
+        g = susp->G_PREV + (susp->G_NEXT - susp->G_PREV) *
+                           (g_count - (susp->G_COUNT - 1));
+        new_flags = PVSHELL_TEST_F(susp);
+        susp->flags |= new_flags;
+        if (new_flags) break;
+        f = PVSHELL_FETCH_F(susp);
+        susp->F_COUNT++; /* count how many samples we have taken */
+        
+        /* now we have f, g, x */
+        *out++ = f * g * susp->X_VALUE;
+    }
+    /* i is the number of samples we acutally computed */
+    *n = i;
+    /* if we computed samples, we want to return them before
+     * returning flags that say we're done or stopped
+     */
+    return (i ? 0 : susp->flags);
+}
+
+
+sound_type snd_phasevocoder(sound_type f, sound_type g, double x)
+{
+    /* we're using 5 doubles of state. The first is a parameter,
+     * and the rest are initialized to zero except for state[2],
+     * aka G_COUNT. This is the number of samples we have read 
+     * from G. Since we're interpolating we need a one-sample
+     * lookahead, and initializing the count to -1 causes an 
+     * extra fetch and hence 1-sample lookahead. This state is copied
+     * into the pvshell structure, so we don't need to allocate
+     * a vector on the heap.
+     */
+    double state[5] = {0, 0, -1, 0, 0};
+    state[0] = x;
+    /* If f and g do not start at the same time, we should really
+     * should do something about it, but we'll just throw an error.
+     * Be careful to allow small differences (within one sample).
+     */
+    if (fabs(f->t0 - g->t0) * f->sr > 0.5) {
+        xlfail("phasevocoder inputs must start at the same time");
+    }
+    /* output the same sample rate and start time as f */
+    return snd_make_pvshell("snd_phasevocoder", f->sr, f->t0,
+                       &pv_fetch, f, g, 
+                       state, sizeof(state) / sizeof(state[0]));
+}