Cleanups in expand()

diff --git a/src/pcm/pcm_rate.c b/src/pcm/pcm_rate.c
index 8d1f11bf0fb7cae706992f9f9742b30bfe3e0642..2e5e73f68e5726052f01083eba21f73e782aaa17 100644 (file)
--- a/src/pcm/pcm_rate.c
+++ b/src/pcm/pcm_rate.c
@@ -42,7 +42,7 @@ const char *_snd_module_pcm_rate = "";
 
 typedef struct {
        int init;
-       int16_t sample;
+       int16_t old_sample, new_sample;
        int sum;
        unsigned int pos;
 } snd_pcm_rate_state_t;
@@ -117,7 +117,8 @@ static snd_pcm_uframes_t snd_pcm_rate_expand(const snd_pcm_channel_area_t *dst_a
                const char *src;
                char *dst;
                int src_step, dst_step;
-               int16_t old_sample = states->sample;
+               int16_t old_sample = states->old_sample;
+               int16_t new_sample = states->new_sample;
                unsigned int pos = states->pos;
                src = snd_pcm_channel_area_addr(src_area, src_offset);
                dst = snd_pcm_channel_area_addr(dst_area, dst_offset);
@@ -126,27 +127,36 @@ static snd_pcm_uframes_t snd_pcm_rate_expand(const snd_pcm_channel_area_t *dst_a
                src_frames1 = 0;
                dst_frames1 = 0;
                if (states->init) {
-                       old_sample = initial_sample(src, getidx);
+                       new_sample = initial_sample(src, getidx);
+                       src_frames1++;
                        states->init = 0;
                }
                while (dst_frames1 < dst_frames) {
                        if (pos >= get_threshold) {
-                               int16_t new_sample;
                                if (src_frames1 == src_frames)
                                        break;
+                               old_sample = new_sample;
                                pos -= get_threshold;
                                goto *get;
 #define GET16_END after_get
 #include "plugin_ops.h"
 #undef GET16_END
                        after_get:
+                               new_sample = sample;
                                src += src_step;
                                src_frames1++;
-                               new_sample = sample;
-                               sample = (old_sample * (DIV - pos) + new_sample * pos) / DIV;
-                               old_sample = new_sample;
-                       } else
-                               sample = old_sample;
+#if 1 /* fast-change interpolation */
+      /* this interpolation gives us better results especially for low-rate sources */
+                               // sample = (((int)old_sample * (DIV - pos)) + ((int)new_sample * pos)) / DIV;
+                               sample = ((int)old_sample + (int)new_sample) / 2;
+                       } else {
+                               sample = new_sample;
+                       }
+#else /* linear interpolation */
+      /* in some cases, a high-band filter is required to remove high noises */
+                       }
+                       sample = (((int)old_sample * (DIV - pos)) + ((int)new_sample * pos)) / DIV;
+#endif
                        goto *put;
 #define PUT16_END after_put
 #include "plugin_ops.h"
@@ -156,7 +166,8 @@ static snd_pcm_uframes_t snd_pcm_rate_expand(const snd_pcm_channel_area_t *dst_a
                        dst_frames1++;
                        pos += DIV;
                }
-               states->sample = old_sample;
+               states->old_sample = old_sample;
+               states->new_sample = new_sample;
                states->pos = pos;
                states++;
        }
@@ -447,7 +458,8 @@ static int snd_pcm_rate_init(snd_pcm_t *pcm)
        unsigned int k;
        for (k = 0; k < pcm->channels; ++k) {
                rate->states[k].sum = 0;
-               rate->states[k].sample = 0;
+               rate->states[k].old_sample = 0;
+               rate->states[k].new_sample = 0;
                rate->states[k].pos = 0;
                rate->states[k].init = 0;
        }