Adjust Volume Control Transfer function to make it a bit slower at very low volumes. Add PDF of transfer function and Mac Grapher source document.

common.c

@@ -186,11 +186,11 @@ double vol2attn(double vol, long max_db, long min_db) {
 // We build the transfer function from one or more lines. We characterise each line with two numbers:
 // the first is where on x the line starts when y=0 (from 0 to -30); the second is where on y the line stops when when x is -30.
 // thus, if the line was characterised as {0,-30}, it would be an identity transfer.
-// Assuming, for example, a dynamic range of lv=-70 to hv=0
+// Assuming, for example, a dynamic range of lv=-60 to hv=0
 // Typically we'll use three lines -- a three order transfer function
 // First: {0,25} giving a gentle slope
-// Second: {-17,-25-(lv+25)/2} giving a faster slope from y=0 at x=-17 to y=-50 at x=-30
-// Third: {-23,lv} giving a fast slope from y=0 at x=-23 to y=-70 at x=-30
+// Second: {-12,-25-(lv+25)/2} giving a faster slope from y=0 at x=-12 to y=-42.5 at x=-30
+// Third: {-19,lv} giving a fast slope from y=0 at x=-19 to y=-60 at x=-30
 
 #define order 3
 
@@ -202,7 +202,7 @@ double vol2attn(double vol, long max_db, long min_db) {
     double first_slope = -2500.0; // this is the slope of the attenuation at the high end -- 25dB for the full rotation.
     if (-range_db>first_slope)
       first_slope = range_db;
-    double lines[order][2] = {{0,first_slope},{-17,first_slope-(range_db+first_slope)/2},{-23,-range_db}};
+    double lines[order][2] = {{0,first_slope},{-12,first_slope-(range_db+first_slope)/2},{-19,-range_db}};
     int i;
     for (i=0;i<order;i++) {
       if (vol<=lines[i][0]) {