Limiter: introduce max buffer.

Signed-off-by: Stefan Westerfeld <stefan@space.twc.de>

src/testlimiter.cc

@@ -17,6 +17,7 @@ class Limiter
 {
   float mx = 1;
   uint look_ahead = 0;
+  vector<float> max_buffer;
   vector<float> buffer;
 public:
   Limiter (int sample_rate)
@@ -28,7 +29,24 @@ public:
   process (const vector<float>& samples)
   {
     for (size_t i = 0; i < samples.size(); i++)
-      buffer.push_back (samples[i]);
+      {
+        buffer.push_back (samples[i]);
+        max_buffer.push_back (1);
+      }
+    for (size_t i = 0; i < buffer.size(); i++)
+      {
+        if (fabs (buffer[i]) > 1)
+          {
+            for (uint j = 0; j < look_ahead; j++)
+              {
+                if (int (i) - int (j) > 0)
+                  {
+                    double alpha = double (j) / look_ahead;
+                    max_buffer[i - j] = max<float> (max_buffer[i - j], fabs (buffer[i]) * (1 - alpha) + 1 * alpha);
+                  }
+              }
+          }
+      }
 
     vector<float> out;
     if (buffer.size() > look_ahead)
@@ -36,24 +54,16 @@ public:
         size_t todo = buffer.size() - look_ahead;
         for (size_t i = 0; i < todo; i++)
           {
-            float xmx = 1;
-            for (uint j = 0; j < look_ahead; j++)
-              xmx = max (fabs (buffer[i + j]), xmx);
-            mx = mx * 0.99 + xmx * 0.01;
+            mx = mx * 0.99 + max_buffer[i] * 0.01;
+            if (mx < max_buffer[i])
+              mx = max_buffer[i];
+
             out.push_back (buffer[i] / mx);
             printf ("%f %f\n", buffer[i], out.back());
           }
-#if 0
-    for (size_t i = 0; i < samples.size(); i++)
-      {
-        if (fabs (samples[i]) > mx)
-          mx = fabs (samples[i]);
-        out.push_back (samples[i] / mx);
-        if (mx > 1)
-          mx = max (mx - 0.01f, 1.f);
-      }
-#endif
+
         buffer.erase (buffer.begin(), buffer.begin() + todo);
+        max_buffer.erase (max_buffer.begin(), max_buffer.begin() + todo);
       }
     return out;
   }