Delay: Add better constraints on delay time and ping-pong feedback

software/src/Audio/AudioDelayExt.h

@@ -17,6 +17,10 @@ template <
   size_t CrossfadeSamples = 2048>
 class AudioDelayExt : public AudioStream {
 public:
+  static constexpr float MAX_DELAY_SECS
+    = BufferLength / AUDIO_SAMPLE_RATE_EXACT;
+  static constexpr float MIN_DELAY_SECS = ChunkSize / AUDIO_SAMPLE_RATE_EXACT;
+
   AudioDelayExt() : AudioStream(1, input_queue_array) {
     delay_secs.fill(OnePole(Interpolated(0.0f, AUDIO_BLOCK_SAMPLES), 0.0002f));
     fb.fill(Interpolated(0.0f, AUDIO_BLOCK_SAMPLES / ChunkSize));
@@ -27,9 +31,10 @@ class AudioDelayExt : public AudioStream {
     // TODO xfade lut should be static
     xfade_in_scalars = new q15_t[CrossfadeSamples];
     xfade_out_scalars = new q15_t[CrossfadeSamples];
-    for (int i = 0; i < 2048; i++) {
+    float n = static_cast<float>(CrossfadeSamples - 1);
+    for (size_t i = 0; i < CrossfadeSamples; i++) {
       float out, in;
-      EqualPowerFade(out, in, i / 2047.0f);
+      EqualPowerFade(out, in, i / n);
       xfade_in_scalars[i] = float_to_q15(in);
       xfade_out_scalars[i] = float_to_q15(out);
     }
@@ -42,11 +47,13 @@ class AudioDelayExt : public AudioStream {
   }
 
   void delay(size_t tap, float secs) {
+    CONSTRAIN(secs, MIN_DELAY_SECS, MAX_DELAY_SECS);
     delay_secs[tap] = secs;
     if (delay_secs[tap].Read() == 0.0f) delay_secs[tap].Reset();
   }
 
   void cf_delay(size_t tap, float secs) {
+    CONSTRAIN(secs, MIN_DELAY_SECS, MAX_DELAY_SECS);
     auto& t = target_delay[tap];
     if (t.phase >= CrossfadeSamples && t.target != secs) {
       // 0.0005f comes from variation

software/src/audio_applets/DelayApplet.h

@@ -3,6 +3,7 @@
 #include "HSicons.h"
 #include "HemisphereAudioApplet.h"
 #include "dsputils.h"
+#include "dsputils_arm.h"
 #include "Audio/AudioDelayExt.h"
 #include "Audio/AudioMixer.h"
 #include "Audio/AudioPassthrough.h"
@@ -57,7 +58,9 @@ class DelayApplet : public HemisphereAudioApplet {
         break;
       default:
       case SECS:
-        d = DelaySecsFromMs(delay_time + delay_cv.Process(delay_time_cv.In()));
+        d = DelaySecsFromMs(
+          delay_time + 0.1f * delay_cv.Process(delay_time_cv.In())
+        );
         break;
     }
     for (int tap = 0; tap < taps; tap++) {
@@ -96,9 +99,14 @@ class DelayApplet : public HemisphereAudioApplet {
 
     if (Channels == STEREO) {
       for (auto& ch : channels) {
-        // The tap mixer has already used equal power mixing on the taps so no
-        // need to do it here.
-        ch.input_mixer.gain(PP_CH, constrain(-total_feedback, 0.0f, 2.0f));
+        // The tap mixer has already used equal power mixing on the taps. With
+        // feedback, we want equal amplitude, so just multiply by one more
+        // factor of equal power and voila (since equal amplitude scalars are
+        // the square roots of equal power)
+        ch.input_mixer.gain(
+          PP_CH,
+          constrain(-total_feedback * EQUAL_POWER_EQUAL_MIX[taps], 0.0f, 2.0f)
+        );
       }
     }
     float dry_gain, wet_gain;
@@ -227,14 +235,18 @@ class DelayApplet : public HemisphereAudioApplet {
             delay_time += knob_accel;
             delay_time *= 16;
 
-            // -8 * 12 * 128 -> ~1 Hz
-            // 6 * 12 * 128 -> ~17kHz
-            CONSTRAIN(delay_time, -8 * 12 * 128, 6 * 12 * 128);
+            CONSTRAIN(
+              delay_time,
+              static_cast<int>(PitchFromDelaySecs(1.0f)),
+              static_cast<int>(PitchFromDelaySecs(MIN_DELAY_SECS)) - 1
+            );
             break;
           case SECS:
             delay_time += knob_accel;
             CONSTRAIN(
-              delay_time, 1, static_cast<int>(MAX_DELAY_SECS * 1000) - 1
+              delay_time,
+              static_cast<int>(MIN_DELAY_SECS * 1000),
+              static_cast<int>(MAX_DELAY_SECS * 1000) - 1
             );
             break;
         }
@@ -305,12 +317,18 @@ class DelayApplet : public HemisphereAudioApplet {
     return &output_stream;
   }
 
+  int PitchFromDelaySecs(float secs) {
+    return -RatioToPitch(C3 * 2 * secs);
+  }
+
   float DelaySecsFromPitch(int pitch) {
-    return constrain(PitchToRatio(-pitch) / (C3 * 2), 0.0f, MAX_DELAY_SECS);
+    return constrain(
+      PitchToRatio(-pitch) / (C3 * 2), MIN_DELAY_SECS, MAX_DELAY_SECS
+    );
   }
 
-  float DelaySecsFromMs(int ms) {
-    return constrain(0.001f * ms, 0.0f, MAX_DELAY_SECS);
+  float DelaySecsFromMs(float ms) {
+    return constrain(0.001f * ms, MIN_DELAY_SECS, MAX_DELAY_SECS);
   }
 
   float DelaySecsFromRatio(int ratio) {
@@ -336,6 +354,12 @@ class DelayApplet : public HemisphereAudioApplet {
   }
 
 private:
+  // Uses 1MB of psram and gives just under 12 secs of delay time.
+  static const size_t DELAY_LENGTH = 1024 * 512;
+  typedef AudioDelayExt<DELAY_LENGTH, 9> DelayStream;
+  static constexpr float MAX_DELAY_SECS = DelayStream::MAX_DELAY_SECS;
+  static constexpr float MIN_DELAY_SECS = DelayStream::MIN_DELAY_SECS;
+
   enum Cursor {
     CLOCK_SOURCE,
     TIME,
@@ -411,15 +435,11 @@ class DelayApplet : public HemisphereAudioApplet {
 
   static const uint8_t PP_CH = 1;
 
-  // Uses 1MB of psram and gives just under 12 secs of delay time.
-  static const size_t DELAY_LENGTH = 1024 * 512;
-  static constexpr float MAX_DELAY_SECS = DELAY_LENGTH / AUDIO_SAMPLE_RATE;
-
   AudioPassthrough<Channels> input_stream;
   struct {
     AudioMixer<2> input_mixer;
     // 9th tap is freeze head
-    AudioDelayExt<DELAY_LENGTH, 9> delay;
+    DelayStream delay;
     AudioMixer<8> taps_mixer;
     AudioMixer<2> wet_dry_mixer;
 

software/src/dsputils.h

@@ -1,7 +1,6 @@
 #pragma once
 #include "extern/fastapprox/fastexp.h"
 #include "extern/fastapprox/fastlog.h"
-#include <arm_math.h>
 
 #define ONE_POLE(out, in, coefficient) out += (coefficient) * ((in) - out);
 
@@ -48,12 +47,6 @@ inline int16_t Clip16(float x) {
   }
 }
 
-inline q15_t float_to_q15(float x) {
-  x *= 32768.0f;
-  x += x > 0.0f ? 0.5f : -0.5f;
-  return (q15_t)(__SSAT((q31_t)(x), 16));
-}
-
 constexpr inline float InterpLinear(float x0, float x1, float t) {
   return t * (x1 - x0) + x0;
 }
@@ -70,37 +63,6 @@ constexpr inline float InterpHermite(
   return ((((a * t) - b_neg) * t + c) * t + x0);
 }
 
-void InterHermiteQ15Vec(
-  q15_t* xm1,
-  q15_t* x0,
-  q15_t* x1,
-  q15_t* x2,
-  q15_t* t,
-  q15_t* out,
-  size_t size
-) {
-  q15_t c[size], v[size], w[size], a[size], b_neg[size];
-
-  arm_sub_q15(x1, xm1, c, size);
-  arm_scale_q15(c, 16384, 0, c, size);
-  arm_sub_q15(x0, x1, v, size);
-  arm_add_q15(c, v, w, size);
-
-  arm_sub_q15(x2, x0, a, size);
-  arm_scale_q15(a, 16384, 0, a, size);
-  arm_add_q15(a, v, a, size);
-  arm_add_q15(a, w, a, size);
-
-  arm_add_q15(w, a, b_neg, size);
-
-  arm_mult_q15(a, t, out, size);
-  arm_sub_q15(out, b_neg, out, size);
-  arm_mult_q15(out, t, out, size);
-  arm_add_q15(out, c, out, size);
-  arm_mult_q15(out, t, out, size);
-  arm_add_q15(out, x0, out, size);
-}
-
 inline float dbToScalar(float db) {
   // pow10(x) = exp(log(10) * x)
   return fastexp(2.302585092994046f * 0.05f * db);

software/src/dsputils_arm.h

@@ -0,0 +1,42 @@
+#pragma once
+
+#include <arm_math.h>
+
+inline q15_t float_to_q15(float x) {
+  x *= 32768.0f;
+  x += x > 0.0f ? 0.5f : -0.5f;
+  return (q15_t)(__SSAT((q31_t)(x), 16));
+}
+
+
+void InterHermiteQ15Vec(
+  q15_t* xm1,
+  q15_t* x0,
+  q15_t* x1,
+  q15_t* x2,
+  q15_t* t,
+  q15_t* out,
+  size_t size
+) {
+  q15_t c[size], v[size], w[size], a[size], b_neg[size];
+
+  arm_sub_q15(x1, xm1, c, size);
+  arm_scale_q15(c, 16384, 0, c, size);
+  arm_sub_q15(x0, x1, v, size);
+  arm_add_q15(c, v, w, size);
+
+  arm_sub_q15(x2, x0, a, size);
+  arm_scale_q15(a, 16384, 0, a, size);
+  arm_add_q15(a, v, a, size);
+  arm_add_q15(a, w, a, size);
+
+  arm_add_q15(w, a, b_neg, size);
+
+  arm_mult_q15(a, t, out, size);
+  arm_sub_q15(out, b_neg, out, size);
+  arm_mult_q15(out, t, out, size);
+  arm_add_q15(out, c, out, size);
+  arm_mult_q15(out, t, out, size);
+  arm_add_q15(out, x0, out, size);
+}
+