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deemph now additionally works at 48k

--- a/src/biquads.c

+++ b/src/biquads.c

@@ -131,10 +131,6 @@

 static int deemph_getopts(sox_effect_t * effp, int argc, char **argv) {

-  priv_t * p = (priv_t *)effp->priv;

-  p->fc    = 5283;

-  p->width = 0.4845;

-  p->gain  = -9.477;

   return lsx_biquad_getopts(effp, argc, argv, 0, 0, 0, 1, 2, "s", filter_deemph);

 }

@@ -162,10 +158,29 @@

 static int start(sox_effect_t * effp)

 {

   priv_t * p = (priv_t *)effp->priv;

-  double w0 = 2 * M_PI * p->fc / effp->in_signal.rate;

-  double A  = exp(p->gain / 40 * log(10.));

-  double alpha = 0, mult = dB_to_linear(max(p->gain, 0));

+  double w0, A, alpha, mult;

+  if (p->filter_type == filter_deemph) { /* See deemph.plt for documentation */

+    if (effp->in_signal.rate == 44100) {

+      p->fc    = 5283;

+      p->width = 0.4845;

+      p->gain  = -9.477;

+    }

+    else if (effp->in_signal.rate == 48000) {

+      p->fc    = 5356;

+      p->width = 0.479;

+      p->gain  = -9.62;

+    }

+    else {

+      lsx_fail("sample rate must be 44100 (audio-CD) or 48000 (DAT)");

+      return SOX_EOF;

+    }

+  }

+

+  w0 = 2 * M_PI * p->fc / effp->in_signal.rate;

+  A  = exp(p->gain / 40 * log(10.));

+  alpha = 0, mult = dB_to_linear(max(p->gain, 0));

+

   if (w0 > M_PI) {

     lsx_fail("frequency must be less than half the sample-rate (Nyquist rate)");

     return SOX_EOF;

@@ -275,12 +290,7 @@

       p->a2 =        (A+1) + (A-1)*cos(w0) - 2*sqrt(A)*alpha;

       break;

-    case filter_deemph:  /* See deemph.plt for documentation */

-      if (effp->in_signal.rate != 44100) {

-        lsx_fail("Sample rate must be 44100 (audio-CD)");

-        return SOX_EOF;

-      }

-      /* Falls through... */

+    case filter_deemph: /* Falls through to high-shelf... */

     case filter_highShelf: /* H(s) = A * (A*s^2 + (sqrt(A)/Q)*s + 1)/(s^2 + (sqrt(A)/Q)*s + A) */

       if (!A)