Add a crossfade option to Buffr Glitch

plugins/buffr_glitch/CHANGELOG.md

@@ -10,6 +10,8 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Added
 
+- Added an option to crossfade the recorded buffer to avoid clicks when looping
+  around.
 - Added an optional velocity sensitive mode.
 
 ### Removed

plugins/buffr_glitch/src/buffer.rs

@@ -33,10 +33,26 @@ pub struct RingBuffer {
     audio_buffers: Vec<Vec<f32>>,
     /// The current playback position in `playback_buffers`.
     next_sample_pos: usize,
-    /// If this is set to `false` then the incoming audio will be recorded to `playback_buffer`
+    /// The length of the crossfade, in samples. After the first this additional samples are
-    /// until it is full. When it wraps around this is set to `true` and the previously recorded
+    /// recorded and faded back into the buffer.
-    /// audio is played back instead.
+    crossfade_length: usize,
-    playback_buffer_ready: bool,
+    /// See [`BufferStatus`].
+    buffer_status: BufferStatus,
+}
+
+#[derive(Debug, Default, Clone, Copy)]
+enum BufferStatus {
+    /// The buffer has not yet been filled and all sample should be recorded into the buffer.
+    #[default]
+    Recording,
+    /// The buffer has wrapped around, but `crossfade_length` is set to 1 or more samples. This
+    /// second pass continues recording, and replaces the buffer's start with a cross faded version
+    /// of that input and the existing contents.
+    Crossfading,
+    /// The buffer has wrapped around once and `crossfade_length` is set to 0, or it has wrapped
+    /// around twice and crossfading is enabled. Samples only need to be read from the buffer, all
+    /// work is done.
+    Ready,
 }
 
 impl RingBuffer {
@@ -71,8 +87,12 @@ impl RingBuffer {
     }
 
     /// Prepare the playback buffers to play back audio at the specified frequency. This resets the
-    /// buffer to record the next `note_period_samples`, which are then looped until the key is released.
+    /// buffer to record the next `note_period_samples`, which are then looped until the key is
-    pub fn prepare_playback(&mut self, frequency: f32) {
+    /// released. The crossfade length is also set at this point since right now we don't record
+    /// more than necessary and can't change this afterwards.
+    pub fn prepare_playback(&mut self, frequency: f32, crossfade_ms: f32) {
+        nih_debug_assert!(frequency > 0.0);
+        nih_debug_assert!(crossfade_ms >= 0.0);
         let note_period_samples = (frequency.recip() * self.sample_rate).ceil() as usize;
 
         // This buffer doesn't need to be cleared since the data is not read until the entire buffer
@@ -82,9 +102,12 @@ impl RingBuffer {
             buffer.resize(note_period_samples, 0.0);
         }
 
-        // The buffer is filled on
+        // The buffer is filled on the first `note_period_samples` calls to `next_sample`, plus a
+        // little more for the crossfade if set
         self.next_sample_pos = 0;
-        self.playback_buffer_ready = false;
+        self.crossfade_length =
+            ((crossfade_ms * self.sample_rate).ceil() as usize).min(note_period_samples);
+        self.buffer_status = BufferStatus::Recording;
     }
 
     /// Read or write a sample from or to the ring buffer, and return the output. On the first loop
@@ -92,8 +115,21 @@ impl RingBuffer {
     /// Afterwards it will read the previously recorded data from the buffer. The read/write
     /// position is advanced whenever the last channel is written to.
     pub fn next_sample(&mut self, channel_idx: usize, input_sample: f32) -> f32 {
-        if !self.playback_buffer_ready {
+        match self.buffer_status {
-            self.audio_buffers[channel_idx][self.next_sample_pos] = input_sample;
+            BufferStatus::Recording => {
+                self.audio_buffers[channel_idx][self.next_sample_pos] = input_sample
+            }
+            BufferStatus::Crossfading if self.next_sample_pos < self.crossfade_length => {
+                // This is an equal power fade between the part of the input after the first loop
+                // and the buffer's existing contents.
+                let crossfade_t = self.next_sample_pos as f32 / (self.crossfade_length - 1) as f32;
+                let new_t = (1.0 - crossfade_t).sqrt();
+                let existing_t = crossfade_t.sqrt();
+
+                self.audio_buffers[channel_idx][self.next_sample_pos] = (input_sample * new_t)
+                    + (self.audio_buffers[channel_idx][self.next_sample_pos] * existing_t);
+            }
+            _ => (),
         }
         let result = self.audio_buffers[channel_idx][self.next_sample_pos];
 
@@ -105,8 +141,12 @@ impl RingBuffer {
             if self.next_sample_pos == self.audio_buffers[0].len() {
                 self.next_sample_pos = 0;
 
-                // At this point the buffer is ready for playback
+                self.buffer_status = match self.buffer_status {
-                self.playback_buffer_ready = true;
+                    BufferStatus::Recording if self.crossfade_length > 0 => {
+                        BufferStatus::Crossfading
+                    }
+                    _ => BufferStatus::Ready,
+                };
             }
         }
 

plugins/buffr_glitch/src/lib.rs

@@ -50,11 +50,17 @@ struct BuffrGlitchParams {
     /// Makes the effect velocity sensitive. `100/127` corresponds to `1.0` gain.
     #[id = "velocity_sensitive"]
     velocity_sensitive: BoolParam,
-
     /// The number of octaves the input signal should be increased or decreased by. Useful to allow
     /// larger grain sizes.
     #[id = "octave_shift"]
     octave_shift: IntParam,
+
+    /// The length of the loop crossfade to use, in milliseconds. This will cause the start of the
+    /// loop to be faded into the last `(crossfade_ms/2)` ms of the loop region, and the part after
+    /// the end to be faded into the first `(crossfade_ms/2)` ms of the loop after the first
+    /// ieration.
+    #[id = "crossfade_ms"]
+    crossfade_ms: FloatParam,
 }
 
 impl Default for BuffrGlitch {
@@ -89,7 +95,6 @@ impl Default for BuffrGlitchParams {
             .with_value_to_string(formatters::v2s_f32_gain_to_db(1))
             .with_string_to_value(formatters::s2v_f32_gain_to_db()),
             velocity_sensitive: BoolParam::new("Velocity Sensitive", false),
-
             octave_shift: IntParam::new(
                 "Octave Shift",
                 0,
@@ -98,6 +103,18 @@ impl Default for BuffrGlitchParams {
                     max: MAX_OCTAVE_SHIFT as i32,
                 },
             ),
+            crossfade_ms: FloatParam::new(
+                "Crossfade",
+                0.0,
+                FloatRange::Skewed {
+                    min: 0.0,
+                    max: 50.0,
+                    factor: FloatRange::skew_factor(-2.5),
+                },
+            )
+            // This doesn't need smoothing because the value is set when the note is held down and cannot be changed afterwards
+            .with_unit(" ms")
+            .with_step_size(0.001),
         }
     }
 }
@@ -180,7 +197,8 @@ impl Plugin for BuffrGlitch {
                         // larger window sizes.
                         let note_frequency = util::midi_note_to_freq(note)
                             * 2.0f32.powi(self.params.octave_shift.value());
-                        self.buffer.prepare_playback(note_frequency);
+                        self.buffer
+                            .prepare_playback(note_frequency, self.params.crossfade_ms.value());
                     }
                     NoteEvent::NoteOff { note, .. } if self.midi_note_id == Some(note) => {
                         // A NoteOff for the currently playing note immediately ends playback