Add calculate_decay_coefficient function to calculate the coefficient…

… for a target exponential decay curve

source/include/signalflow/core/util.h

@@ -42,6 +42,10 @@ void signalflow_save_block_to_wav_file(sample *block, int num_samples, std::stri
 float signalflow_array_sum(float *array, size_t size);
 float signalflow_array_mean(float *array, size_t size);
 
+float signalflow_calculate_decay_coefficient(float decay_time,
+                                             unsigned int sample_rate,
+                                             float decay_level);
+
 std::vector<int> signalflow_binary_sequence_to_vector(std::string binary);
 
 }

source/src/core/util.cpp

@@ -204,4 +204,20 @@ float signalflow_array_mean(float *array, size_t size)
     return sum / size;
 }
 
-} /* namespace signalflow */
+float signalflow_calculate_decay_coefficient(float decay_time,
+                                             unsigned int sample_rate,
+                                             float decay_level)
+{
+    // # linear to db = 20 x log10(lin)
+    // # db to linear = 10 ^ (db / 20)
+    // # for a floor of -60dB, want to find x such that x^y = 10^(-3)
+    // # and y is the required delay duration in samples
+    // #  = 0.001^(1/y)
+    //     decay_time_samples = int(decay_time * sample_rate)
+    //           return np.power(envelope_floor, 1.0 / decay_time_samples)
+    float decay_time_samples = decay_time * sample_rate;
+    return powf(decay_level, 1.0f / decay_time_samples);
+}
+
+}
+/* namespace signalflow */

source/src/python/util.cpp

@@ -31,6 +31,12 @@ void init_python_util(py::module &m)
     m.def(
         "random_exponential", [](float from, float to) { return random_exponential(from, to); }, R"pbdoc(Return a random number, exponentially distributed across a fixed range)pbdoc");
 
+    m.def(
+        "calculate_decay_coefficient", [](float decay_time, unsigned int sample_rate, float decay_level) {
+            return signalflow_calculate_decay_coefficient(decay_time, sample_rate, decay_level);
+        },
+        R"pbdoc(Calculate the coefficient required for an exponential decay curve, with duration of decay_time and final value of decay_level (typically 0.001 or -60dB))pbdoc");
+
     py::class_<KDTree>(m, "KDTree", "A KDTree structure")
         .def(py::init<std::vector<std::vector<float>>>(), "data"_a = nullptr)
         .def("get_nearest", &KDTree::get_nearest, "target"_a);