Crone meter scaling (#885)

* add proper audio scaling (untested)

* uncrustify device_crow

* add pragma to ignore  in device_crow.c

* give weaver.c the same pragma treatment, removing a few lines

* fix stuff

* skip redundant abs() in AudioMeter

* use audio meter in amp poll

.gitignore

@@ -24,8 +24,6 @@ crone/\.idea/
 
 crone/cmake-build-debug/
 
-crone/dsp/
-
 crone/build-debinfo/
 
 crone/build-release/

crone/CMakeLists.txt

@@ -24,6 +24,7 @@ set (SRC src/main.cpp
         src/SoftCutClient.cpp
         src/SoftCutClient.h
         src/Poll.h
+        src/Taper.cpp
         src/Window.cpp
         )
 

crone/dsp/workbench/dbfs_meter.py

@@ -0,0 +1,48 @@
+# dbFS metering scale following IEC-60268-18
+
+from scipy import interpolate
+import numpy as np
+import matplotlib.pyplot as plt
+
+# this dictionary associates dbFS values with deflection percentage
+db_deflect = {
+    0: 100,
+    -10: 75,
+    -20: 50,
+    -30: 30,
+    -40: 15,
+    -50: 7.5,
+    -60: 5
+}
+
+def dbamp(db):
+    return pow(10, db * 0.05)
+
+# we want to take linear amplitude and return deflection.
+# we'll take the IEC table, convert dbFS to amp, and interpolate equal points.
+
+db = list(db_deflect.keys())
+db.sort()
+pos = list(map(lambda x: db_deflect[x], db))
+amp = list(map(lambda x: dbamp(x), db))
+
+# we want zero amp == zero pos.
+# insert an additional point for interpolation source.
+amp.insert(0, 0)
+pos.insert(0, 0)
+
+interpf  = interpolate.interp1d(amp, pos)
+n = 32 # table doesn't have to be huge.
+x = np.linspace(0, 1, n)
+y = interpf(x)
+
+plt.plot(x, y, '-o')
+plt.grid(True)
+plt.show()
+
+# export the table, scaled to unit range
+print("const float amp_meter_table[] = { ")
+print("\t", end='')
+for p in y:
+    print('{}, '.format(p*0.01), end='')
+print("\n}")

crone/dsp/workbench/requirements.txt

@@ -0,0 +1,8 @@
+cycler==0.10.0
+kiwisolver==1.1.0
+matplotlib==3.1.1
+numpy==1.17.2
+pyparsing==2.4.2
+python-dateutil==2.8.0
+scipy==1.3.1
+six==1.12.0

crone/src/OscInterface.cpp

@@ -14,6 +14,7 @@
 
 #include "Commands.h"
 #include "OscInterface.h"
+#include "Taper.h"
 
 using namespace crone;
 using softcut::FadeCurves;
@@ -58,12 +59,11 @@ void OscInterface::init(MixerClient *m, SoftCutClient *sc)
     vuPoll = std::make_unique<Poll>("vu");
     vuPoll->setCallback([](const char* path){
         auto vl = mixerClient->getVuLevels();
-        // FIXME: perform exponential scaling here?
         char l[4];
-        l[0] = (uint8_t)(64*vl->absPeakIn[0].load());
-        l[1] = (uint8_t)(64*vl->absPeakIn[1].load());
-        l[2] = (uint8_t)(64*vl->absPeakIn[2].load());
-        l[3] = (uint8_t)(64*vl->absPeakIn[3].load());
+        l[0] = (uint8_t)(64*AudioMeter::getPos(vl->absPeakIn[0].load()));
+        l[1] = (uint8_t)(64*AudioMeter::getPos(vl->absPeakIn[1].load()));
+        l[2] = (uint8_t)(64*AudioMeter::getPos(vl->absPeakIn[2].load()));
+        l[3] = (uint8_t)(64*AudioMeter::getPos(vl->absPeakIn[3].load()));
         lo_blob bl = lo_blob_new(sizeof(l), l);
         lo_send(matronAddress, path, "b", bl);
         vl->clear();

crone/src/Taper.cpp

@@ -0,0 +1,9 @@
+#include "Taper.h"
+
+using namespace crone;
+
+const unsigned int AudioMeter::ampPosTableSize = 32;
+
+const float AudioMeter::ampPosTable[] = { 
+	0.0, 0.3018581857609061, 0.3962114306366651, 0.49056467551242405, 0.5335667553239385, 0.5708631501283147, 0.6081595449326909, 0.645455939737067, 0.6827523345414431, 0.7200487293458193, 0.7523227322011328, 0.7641168878106025, 0.7759110434200724, 0.7877051990295422, 0.7994993546390121, 0.8112935102484821, 0.8230876658579519, 0.8348818214674217, 0.8466759770768917, 0.8584701326863615, 0.8702642882958314, 0.8820584439053013, 0.8938525995147711, 0.9056467551242411, 0.9174409107337109, 0.9292350663431808, 0.9410292219526505, 0.9528233775621207, 0.9646175331715904, 0.9764116887810603, 0.9882058443905303, 1.0, 
+};

crone/src/Taper.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include "Utilities.h"
+
+namespace  crone {
+    class AudioMeter {
+    private:
+        static const float ampPosTable[];
+        static const unsigned int ampPosTableSize;
+    public:
+        // get position on perceptual taper scale (IEC-60268)
+        // assumption: amp >= 0.f
+        static float getPos(float amp) {
+            // FIXME: should we return a special value for clipping?
+            if (amp > 1.f) { return 1.f; }
+            return LUT<float>::lookupLinear(amp, ampPosTable, ampPosTableSize);
+        }
+    };
+
+}

crone/src/Utilities.h

@@ -229,4 +229,25 @@ namespace crone {
         }
     };
 
-}
+}
+
+// simple lookup table class
+template<typename T>
+class LUT {
+public:
+    // look up a value from a table with normalized position
+    // warning: no bounds checking on position!
+    // must be in [0, 1] or you get garbage.
+    static T lookupLinear(float x, const T* tab, unsigned int size) {
+	const unsigned int size_1 = size-1;
+	const float fidx = x * size_1;
+	const unsigned int idx = static_cast<unsigned int>(fidx);
+	if (idx >= size_1) {
+	    return tab[size_1];
+	}
+	const float a = tab[idx];
+	const float b = tab[idx+1];
+	const float f = fidx - static_cast<float>(idx);
+	return a + (b-1)*f;
+    }
+};

crone/wscript

@@ -14,6 +14,7 @@ def build(bld):
         'src/Commands.cpp',
         'src/MixerClient.cpp',
         'src/SoftCutClient.cpp',
+        'src/Taper.cpp',
         'src/Window.cpp',
         'src/softcut/FadeCurves.cpp',
         'src/softcut/SoftCutHead.cpp',