Factor first order shelving filter code out for easier reuse and replace the crossfeed filter with it. Crossfeed _should_ still sound the same, so please do tell if it doesn't.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@12674 a1c6a512-1295-4272-9138-f99709370657

5 files changed, 78 insertions, 82 deletions

diff --git a/apps/dsp.c b/apps/dsp.c
index ca494e553f..9e410f879a 100644
--- a/apps/dsp.c
+++ b/apps/dsp.c
@@ -787,13 +787,27 @@ void dsp_set_crossfeed_direct_gain(int gain)
         crossfeed_data.gain = 0x7fffffff;
 }
 
+/* Both gains should be below 0 dB (when inverted) */
 void dsp_set_crossfeed_cross_params(long lf_gain, long hf_gain, long cutoff)
 {
-    long g1 = get_replaygain_int(lf_gain * -10) << 3;
-    long g2 = get_replaygain_int(hf_gain * -10) << 3;
-
-    filter_shelf_coefs(0xffffffff/NATIVE_FREQUENCY*cutoff, g1, g2,
-                       crossfeed_data.coefs);
+    int32_t *c = crossfeed_data.coefs;
+    long scaler = get_replaygain_int(lf_gain * -10) << 7;
+
+    cutoff = 0xffffffff/NATIVE_FREQUENCY*cutoff;
+    hf_gain -= lf_gain;
+    /* Divide cutoff by sqrt(10^(-hf_gain/20)) to place cutoff at the -3 dB
+     * point instead of shelf midpoint. This is for compatibility with the old
+     * crossfeed shelf filter and should be removed if crossfeed settings are
+     * ever made incompatible for any other good reason.
+     */
+    cutoff = DIV64(cutoff, get_replaygain_int(-hf_gain*5), 24);
+    filter_shelf_coefs(cutoff, -hf_gain, false, c);
+    /* Scale coefs by LF gain and shift them to s0.31 format. We have no gains
+     * over 1 and can do this safely
+     */
+    c[0] = FRACMUL_SHL(c[0], scaler, 4);
+    c[1] = FRACMUL_SHL(c[1], scaler, 4);
+    c[2] <<= 4;
 }
 
 /* Combine all gains to a global gain. */
diff --git a/apps/eq.c b/apps/eq.c
index e06bd3e09e..b03a651812 100644
--- a/apps/eq.c
+++ b/apps/eq.c
@@ -118,33 +118,42 @@ static long fsincos(unsigned long phase, long *cos) {
     return y;
 }
 
-/**
- * Calculate first order shelving filter coefficients.
- * Note that the filter is not compatible with the eq_filter routine.
- * @param cutoff a value from 0 to 0x80000000, where 0 represents 0 Hz and
- * 0x80000000 represents the Nyquist frequency (samplerate/2).
- * @param ad gain at 0 Hz. s3.27 fixed point.
- * @param an gain at Nyquist frequency. s3.27 fixed point.
- * @param c pointer to coefficient storage. The coefs are s0.31 format.
+/** 
+ * Calculate first order shelving filter. Filter is not directly usable by the
+ * eq_filter() function.
+ * @param cutoff shelf midpoint frequency. See eq_pk_coefs for format.
+ * @param A decibel value multiplied by ten, describing gain/attenuation of
+ * shelf. Max value is 24 dB.
+ * @param low true for low-shelf filter, false for high-shelf filter.
+ * @param c pointer to coefficient storage. Coefficients are s4.27 format.
  */
-void filter_shelf_coefs(unsigned long cutoff, long ad, long an, int32_t *c)
+void filter_shelf_coefs(unsigned long cutoff, long A, bool low, int32_t *c)
 {
-    const long one = 1 << 27;
-    long a0, a1;
-    long b0, b1;
-    long s, cs;
-    s = fsincos(cutoff, &cs) >> 4;
-    cs = one + (cs >> 4);
-
-    /* For max A = 4 (24 dB) */
-    b0 = FRACMUL_SHL(ad, s, 4) + FRACMUL_SHL(an, cs, 4);
-    b1 = FRACMUL_SHL(ad, s, 4) - FRACMUL_SHL(an, cs, 4);
-    a0 = s + cs;
-    a1 = s - cs;
+    long sin, cos;
+    int32_t b0, b1, a0, a1; /* s3.28 */
+    const long g = get_replaygain_int(A*5) << 4; /* 10^(db/40), s3.28 */
+
+    sin = fsincos(cutoff/2, &cos);
+    if (low) {
+        const int32_t sin_div_g = DIV64(sin, g, 25);
+        cos >>= 3;
+        b0 = FRACMUL(sin, g) + cos;   /* 0.25 .. 4.10 */
+        b1 = FRACMUL(sin, g) - cos;   /* -1 .. 3.98 */
+        a0 = sin_div_g + cos;         /* 0.25 .. 4.10 */
+        a1 = sin_div_g - cos;         /* -1 .. 3.98 */
+    } else {
+        const int32_t cos_div_g = DIV64(cos, g, 25);
+        sin >>= 3;
+        b0 = sin + FRACMUL(cos, g);   /* 0.25 .. 4.10 */
+        b1 = sin - FRACMUL(cos, g);   /* -3.98 .. 1 */
+        a0 = sin + cos_div_g;         /* 0.25 .. 4.10 */
+        a1 = sin - cos_div_g;         /* -3.98 .. 1 */
+    }
 
-    c[0] = DIV64(b0, a0, 31);
-    c[1] = DIV64(b1, a0, 31);
-    c[2] = -DIV64(a1, a0, 31);
+    const int32_t rcp_a0 = DIV64(1, a0, 57); /* 0.24 .. 3.98, s2.29 */
+    *c++ = FRACMUL_SHL(b0, rcp_a0, 1);       /* 0.063 .. 15.85 */
+    *c++ = FRACMUL_SHL(b1, rcp_a0, 1);       /* -15.85 .. 15.85 */
+    *c++ = -FRACMUL_SHL(a1, rcp_a0, 1);      /* -1 .. 1 */
 }
 
 #ifdef HAVE_SW_TONE_CONTROLS
@@ -163,41 +172,26 @@ void filter_shelf_coefs(unsigned long cutoff, long ad, long an, int32_t *c)
 void filter_bishelf_coefs(unsigned long cutoff_low, unsigned long cutoff_high,
                           long A_low, long A_high, long A, int32_t *c)
 {
-    long sin1, cos2;        /* s0.31 */
-    long cos1, sin2;        /* s3.28 */
-    int32_t b0, b1, b2, b3; /* s3.28 */
-    int32_t a0, a1, a2, a3;
-    const long gd = get_replaygain_int(A_low*5) << 4; /* 10^(db/40), s3.28 */
-    const long gn = get_replaygain_int(A_high*5) << 4; /* 10^(db/40), s3.28 */
     const long g = get_replaygain_int(A*10) << 7; /* 10^(db/20), s0.31 */
+    int32_t c_ls[3], c_hs[3];
 
-    sin1 = fsincos(cutoff_low/2, &cos1);
-    sin2 = fsincos(cutoff_high/2, &cos2) >> 3;
-    cos1 >>= 3;
-
-    /* lowshelf filter, ranges listed are for all possible cutoffs */
-    b0 = FRACMUL(sin1, gd) + cos1;   /* 0.25 .. 4.10 */
-    b1 = FRACMUL(sin1, gd) - cos1;   /* -1 .. 3.98 */
-    a0 = DIV64(sin1, gd, 25) + cos1; /* 0.25 .. 4.10 */
-    a1 = DIV64(sin1, gd, 25) - cos1; /* -1 .. 3.98 */
-
-    /* highshelf filter */
-    b2 = sin2 + FRACMUL(cos2, gn);   /* 0.25 .. 4.10 */
-    b3 = sin2 - FRACMUL(cos2, gn);   /* -3.98 .. 1 */
-    a2 = sin2 + DIV64(cos2, gn, 25); /* 0.25 .. 4.10 */
-    a3 = sin2 - DIV64(cos2, gn, 25); /* -3.98 .. 1 */
+    filter_shelf_coefs(cutoff_low, A_low, true, c_ls);
+    filter_shelf_coefs(cutoff_high, A_high, false, c_hs);
+    c_ls[0] = FRACMUL(g, c_ls[0]);
+    c_ls[1] = FRACMUL(g, c_ls[1]);
 
     /* now we cascade the two first order filters to one second order filter
      * which can be used by eq_filter(). these resulting coefficients have a
      * really wide numerical range, so we use a fixed point format which will
      * work for the selected cutoff frequencies (in dsp.c) only.
      */
-    const int32_t rcp_a0 = DIV64(1, FRACMUL(a0, a2), 53); /* s3.28 */
-    *c++ = FRACMUL(g, FRACMUL_SHL(FRACMUL(b0, b2), rcp_a0, 5));
-    *c++ = FRACMUL(g, FRACMUL_SHL(FRACMUL(b0, b3) + FRACMUL(b1, b2), rcp_a0, 5));
-    *c++ = FRACMUL(g, FRACMUL_SHL(FRACMUL(b1, b3), rcp_a0, 5));
-    *c++ = -FRACMUL_SHL(FRACMUL(a0, a3) + FRACMUL(a1, a2), rcp_a0, 5);
-    *c++ = -FRACMUL_SHL(FRACMUL(a1, a3), rcp_a0, 5);
+    const int32_t b0 = c_ls[0], b1 = c_ls[1], b2 = c_hs[0], b3 = c_hs[1];
+    const int32_t a0 = c_ls[2], a1 = c_hs[2];
+    *c++ = FRACMUL_SHL(b0, b2, 4);
+    *c++ = FRACMUL_SHL(b0, b3, 4) + FRACMUL_SHL(b1, b2, 4);
+    *c++ = FRACMUL_SHL(b1, b3, 4);
+    *c++ = a0 + a1;
+    *c++ = -FRACMUL_SHL(a0, a1, 4);
 }
 #endif
 
@@ -276,7 +270,7 @@ void eq_ls_coefs(unsigned long cutoff, unsigned long Q, long db, int32_t *c)
     a2 = ap1 + FRACMUL(am1, cs) - twosqrtalpha;
 
     /* [0.1 .. 1.99] */
-    const long rcp_a0 = DIV64(1, a0, 55); /* s1.30 */
+    const long rcp_a0 = DIV64(1, a0, 55);    /* s1.30 */
     *c++ = FRACMUL_SHL(b0, rcp_a0, 2);       /* [0.06 .. 15.9] */
     *c++ = FRACMUL_SHL(b1, rcp_a0, 2);       /* [-2 .. 31.7] */
     *c++ = FRACMUL_SHL(b2, rcp_a0, 2);       /* [0 .. 15.9] */
@@ -315,7 +309,7 @@ void eq_hs_coefs(unsigned long cutoff, unsigned long Q, long db, int32_t *c)
     a2 = ap1 - FRACMUL(am1, cs) - twosqrtalpha;
 
     /* [0.1 .. 1.99] */
-    const long rcp_a0 = DIV64(1, a0, 55); /* s1.30 */
+    const long rcp_a0 = DIV64(1, a0, 55);    /* s1.30 */
     *c++ = FRACMUL_SHL(b0, rcp_a0, 2);       /* [0 .. 16] */
     *c++ = FRACMUL_SHL(b1, rcp_a0, 2);       /* [-31.7 .. 2] */
     *c++ = FRACMUL_SHL(b2, rcp_a0, 2);       /* [0 .. 16] */
diff --git a/apps/eq.h b/apps/eq.h
index 83d235959d..b895b44b97 100644
--- a/apps/eq.h
+++ b/apps/eq.h
@@ -34,7 +34,7 @@ struct eqfilter {
     int32_t history[2][4];
 };
 
-void filter_shelf_coefs(unsigned long cutoff, long ad, long an, int32_t *c);
+void filter_shelf_coefs(unsigned long cutoff, long A, bool low, int32_t *c);
 void filter_bishelf_coefs(unsigned long cutoff_low, unsigned long cutoff_high,
                           long A_low, long A_high, long A, int32_t *c);
 void eq_pk_coefs(unsigned long cutoff, unsigned long Q, long db, int32_t *c);
diff --git a/apps/settings.c b/apps/settings.c
index a420e46281..331229190a 100644
--- a/apps/settings.c
+++ b/apps/settings.c
@@ -829,8 +829,7 @@ void settings_apply(void)
     dsp_set_crossfeed(global_settings.crossfeed);
     dsp_set_crossfeed_direct_gain(global_settings.crossfeed_direct_gain);
     dsp_set_crossfeed_cross_params(global_settings.crossfeed_cross_gain,
-                                   global_settings.crossfeed_cross_gain
-                                   + global_settings.crossfeed_hf_attenuation,
+                                   global_settings.crossfeed_hf_attenuation,
                                    global_settings.crossfeed_hf_cutoff);
 
     dsp_set_eq(global_settings.eq_enabled);
diff --git a/apps/settings_list.c b/apps/settings_list.c
index ae811bad4e..6594db7aa3 100644
--- a/apps/settings_list.c
+++ b/apps/settings_list.c
@@ -262,23 +262,12 @@ static void crossfeed_format(char* buffer, int buffer_size, int value,
     snprintf(buffer, buffer_size, "%s%d.%d %s", value == 0 ? " " : "-",
         value / 10, value % 10, unit);
 }
-static void crossfeed_cross_gain_helper(int val)
+static void crossfeed_cross_set(int val)
 {
-    dsp_set_crossfeed_cross_params(val,
-        val + global_settings.crossfeed_hf_attenuation,
-        global_settings.crossfeed_hf_cutoff);
-}
-static void crossfeed_hf_att_helper(int val)
-{
-    dsp_set_crossfeed_cross_params(global_settings.crossfeed_cross_gain,
-        global_settings.crossfeed_cross_gain + val,
-        global_settings.crossfeed_hf_cutoff);
-}
-static void crossfeed_hf_cutoff_helper(int val)
-{
-    dsp_set_crossfeed_cross_params(global_settings.crossfeed_cross_gain,
-        global_settings.crossfeed_cross_gain
-            + global_settings.crossfeed_hf_attenuation, val);
+   (void)val;
+   dsp_set_crossfeed_cross_params(global_settings.crossfeed_cross_gain,
+                                  global_settings.crossfeed_hf_attenuation,
+                                  global_settings.crossfeed_hf_cutoff);
 }
 
 static void replaygain_preamp_format(char* buffer, int buffer_size, int value,
@@ -828,7 +817,7 @@ const struct settings_list settings[] = {
     INT_SETTING(0, crossfade_fade_out_duration, LANG_CROSSFADE_FADE_OUT_DURATION, 0,
         "crossfade fade out duration", UNIT_SEC, 0, 15, 1, NULL, NULL, NULL),
     CHOICE_SETTING(0, crossfade_fade_out_mixmode, LANG_CROSSFADE_FADE_OUT_MODE,
-        0, "crossfade fade out mode", "crossfade,mix" ,NULL, 2,
+        0, "crossfade fade out mode", "crossfade,mix", NULL, 2,
         ID2P(LANG_CROSSFADE), ID2P(LANG_MIX)),
         
     /* crossfeed */
@@ -839,13 +828,13 @@ const struct settings_list settings[] = {
                     crossfeed_format, NULL, dsp_set_crossfeed_direct_gain),
     INT_SETTING(0, crossfeed_cross_gain, LANG_CROSSFEED_CROSS_GAIN, 60,
                     "crossfeed cross gain", UNIT_DB, 30, 120, 5,
-                    crossfeed_format, NULL, crossfeed_cross_gain_helper),
+                    crossfeed_format, NULL, crossfeed_cross_set),
     INT_SETTING(0, crossfeed_hf_attenuation, LANG_CROSSFEED_HF_ATTENUATION, 160,
                     "crossfeed hf attenuation", UNIT_DB, 60, 240, 5,
-                    crossfeed_format, NULL, crossfeed_hf_att_helper),
-    INT_SETTING(0, crossfeed_hf_cutoff, LANG_CROSSFEED_HF_CUTOFF,700,
+                    crossfeed_format, NULL, crossfeed_cross_set),
+    INT_SETTING(0, crossfeed_hf_cutoff, LANG_CROSSFEED_HF_CUTOFF, 700,
                     "crossfeed hf cutoff", UNIT_HERTZ, 500, 2000, 100,
-                    NULL, NULL, crossfeed_hf_cutoff_helper),
+                    NULL, NULL, crossfeed_cross_set),
     /* equalizer */
     OFFON_SETTING(0,eq_enabled,LANG_EQUALIZER_ENABLED,false,"eq enabled",NULL),
     INT_SETTING(0, eq_precut, LANG_EQUALIZER_PRECUT, 0, "eq precut",