Add basic limiter prototype.

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

src/Makefile.am

@@ -9,7 +9,7 @@ COMMON_LIBS = $(SNDFILE_LIBS) $(FFTW_LIBS) $(LIBGCRYPT_LIBS) $(LIBMPG123_LIBS)
 audiowmark_SOURCES = audiowmark.cc wmget.cc wmadd.cc $(COMMON_SRC)
 audiowmark_LDFLAGS = $(COMMON_LIBS)
 
-noinst_PROGRAMS = testconvcode testrandom testmp3 teststream
+noinst_PROGRAMS = testconvcode testrandom testmp3 teststream testlimiter
 
 testconvcode_SOURCES = testconvcode.cc $(COMMON_SRC)
 testconvcode_LDFLAGS = $(COMMON_LIBS)
@@ -22,3 +22,6 @@ testmp3_LDFLAGS = $(COMMON_LIBS)
 
 teststream_SOURCES = teststream.cc $(COMMON_SRC)
 teststream_LDFLAGS = $(COMMON_LIBS)
+
+testlimiter_SOURCES = testlimiter.cc $(COMMON_SRC)
+testlimiter_LDFLAGS = $(COMMON_LIBS)

src/testlimiter.cc

+#include <string>
+#include <vector>
+#include <sndfile.h>
+#include <assert.h>
+#include <math.h>
+
+#include "sfinputstream.hh"
+#include "stdoutwavoutputstream.hh"
+#include "utils.hh"
+
+using std::string;
+using std::vector;
+using std::max;
+using std::min;
+
+class Limiter
+{
+  float mx = 1;
+  uint look_ahead = 0;
+  vector<float> buffer;
+public:
+  Limiter (int sample_rate)
+  {
+    look_ahead = sample_rate * 0.005;
+    assert (look_ahead >= 1);
+  }
+  vector<float>
+  process (const vector<float>& samples)
+  {
+    for (size_t i = 0; i < samples.size(); i++)
+      buffer.push_back (samples[i]);
+
+    vector<float> out;
+    if (buffer.size() > look_ahead)
+      {
+        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;
+            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);
+      }
+    return out;
+  }
+};
+
+int
+main (int argc, char **argv)
+{
+  SFInputStream in;
+  StdoutWavOutputStream out;
+
+  std::string filename = (argc >= 2) ? argv[1] : "-";
+  Error err = in.open (filename.c_str());
+  if (err)
+    {
+      fprintf (stderr, "teststream: open input failed: %s\n", err.message());
+      return 1;
+    }
+  err = out.open (in.n_channels(), in.sample_rate(), 16, in.n_frames());
+  if (err)
+    {
+      fprintf (stderr, "teststream: open output failed: %s\n", err.message());
+      return 1;
+    }
+  Limiter limiter (in.sample_rate());
+  vector<float> samples;
+  do
+    {
+      in.read_frames (samples, 1024);
+      for (auto& s: samples)
+        s *= 1.1;
+      samples = limiter.process (samples);
+      //out.write_frames (samples);
+    }
+  while (samples.size());
+}