Add a non-functional STFT to Spectral Compressor

Cargo.lock

@@ -3623,6 +3623,7 @@ version = "0.1.0"
 dependencies = [
  "nih_plug",
  "nih_plug_vizia",
+ "realfft",
 ]
 
 [[package]]

plugins/spectral_compressor/Cargo.toml

@@ -11,3 +11,5 @@ crate-type = ["cdylib"]
 [dependencies]
 nih_plug = { path = "../../", features = ["assert_process_allocs"] }
 nih_plug_vizia = { path = "../../nih_plug_vizia" }
+
+realfft = "3.0"

plugins/spectral_compressor/src/lib.rs

@@ -16,23 +16,124 @@
 
 use nih_plug::prelude::*;
 use nih_plug_vizia::ViziaState;
+use realfft::num_complex::Complex32;
+use realfft::{ComplexToReal, RealFftPlanner, RealToComplex};
 use std::sync::Arc;
 
 mod editor;
 
+const MIN_WINDOW_ORDER: usize = 6;
+#[allow(dead_code)]
+const MIN_WINDOW_SIZE: usize = 1 << MIN_WINDOW_ORDER; // 64
+const DEFAULT_WINDOW_ORDER: usize = 12;
+#[allow(dead_code)]
+const DEFAULT_WINDOW_SIZE: usize = 1 << DEFAULT_WINDOW_ORDER; // 4096
+const MAX_WINDOW_ORDER: usize = 15;
+const MAX_WINDOW_SIZE: usize = 1 << MAX_WINDOW_ORDER; // 32768
+
+const MIN_OVERLAP_ORDER: usize = 2;
+#[allow(dead_code)]
+const MIN_OVERLAP_TIMES: usize = 2 << MIN_OVERLAP_ORDER; // 4
+const DEFAULT_OVERLAP_ORDER: usize = 3;
+#[allow(dead_code)]
+const DEFAULT_OVERLAP_TIMES: usize = 1 << DEFAULT_OVERLAP_ORDER; // 4
+const MAX_OVERLAP_ORDER: usize = 5;
+#[allow(dead_code)]
+const MAX_OVERLAP_TIMES: usize = 1 << MAX_OVERLAP_ORDER; // 32
+
+/// This is a port of <https://github.com/robbert-vdh/spectral-compressor/>.
 struct SpectralCompressor {
     params: Arc<SpectralCompressorParams>,
     editor_state: Arc<ViziaState>,
+
+    /// An adapter that performs most of the overlap-add algorithm for us.
+    stft: util::StftHelper,
+    /// Contains a Hann window function of the current window length, passed to the overlap-add
+    /// helper. Allocated with a `MAX_WINDOW_SIZE` initial capacity.
+    window_function: Vec<f32>,
+
+    /// The algorithms for the FFT and IFFT operations, for each supported order so we can switch
+    /// between them without replanning or allocations. Initialized during `initialize()`.
+    plan_for_order: Option<[Plan; MAX_WINDOW_ORDER - MIN_WINDOW_ORDER + 1]>,
+    /// The output of our real->complex FFT.
+    complex_fft_buffer: Vec<Complex32>,
 }
 
-#[derive(Params, Default)]
-struct SpectralCompressorParams {}
+/// An FFT plan for a specific window size, all of which will be precomputed during initilaization.
+struct Plan {
+    /// The algorithm for the FFT operation.
+    r2c_plan: Arc<dyn RealToComplex<f32>>,
+    /// The algorithm for the IFFT operation.
+    c2r_plan: Arc<dyn ComplexToReal<f32>>,
+}
+
+#[derive(Params)]
+struct SpectralCompressorParams {
+    /// Gain applied just before the DFT as part of the STFT process.
+    #[id = "input_db"]
+    input_gain_db: FloatParam,
+    /// Makeup gain applied after the IDFT in the STFT process. If automatic makeup gain is enabled,
+    /// then this acts as an offset on top of that.
+    #[id = "output_db"]
+    output_gain_db: FloatParam,
+    /// Try to automatically compensate for low thresholds. Doesn't do anything when sidechaining is
+    /// active.
+    #[id = "auto_makeup"]
+    auto_makeup_gain: BoolParam,
+    /// How much of the dry signal to mix in with the processed signal. The mixing is done after
+    /// applying the output gain. In other words, the dry signal is not gained in any way.
+    #[id = "dry_wet"]
+    dry_wet_ratio: FloatParam,
+}
 
 impl Default for SpectralCompressor {
     fn default() -> Self {
         Self {
             params: Arc::new(SpectralCompressorParams::default()),
             editor_state: editor::default_state(),
+
+            // These two will be set to the correct values in the initialize function
+            stft: util::StftHelper::new(Self::DEFAULT_NUM_OUTPUTS as usize, MAX_WINDOW_SIZE, 0),
+            window_function: Vec::with_capacity(MAX_WINDOW_SIZE),
+
+            // This is initialized later since we don't want to do non-trivial computations before
+            // the plugin is initialized
+            plan_for_order: None,
+            complex_fft_buffer: Vec::with_capacity(MAX_WINDOW_SIZE / 2 + 1),
+        }
+    }
+}
+
+impl Default for SpectralCompressorParams {
+    fn default() -> Self {
+        Self {
+            // We don't need any smoothing for these parameters as the overlap-add process will
+            // already act as a form of smoothing
+            input_gain_db: FloatParam::new(
+                "Input Gain",
+                0.0,
+                FloatRange::Linear {
+                    min: -50.0,
+                    max: 50.0,
+                },
+            )
+            .with_unit(" dB")
+            .with_step_size(0.1),
+            output_gain_db: FloatParam::new(
+                "Output Gain",
+                0.0,
+                FloatRange::Linear {
+                    min: -50.0,
+                    max: 50.0,
+                },
+            )
+            .with_unit(" dB")
+            .with_step_size(0.1),
+            auto_makeup_gain: BoolParam::new("Auto Makeup Gain", true),
+            dry_wet_ratio: FloatParam::new("Mix", 1.0, FloatRange::Linear { min: 0.0, max: 1.0 })
+                .with_unit("%")
+                .with_value_to_string(formatters::v2s_f32_percentage(0))
+                .with_string_to_value(formatters::s2v_f32_percentage()),
         }
     }
 }
@@ -63,17 +164,134 @@ impl Plugin for SpectralCompressor {
         config.num_input_channels == config.num_output_channels && config.num_input_channels > 0
     }
 
+    fn initialize(
+        &mut self,
+        bus_config: &BusConfig,
+        _buffer_config: &BufferConfig,
+        context: &mut impl InitContext,
+    ) -> bool {
+        // This plugin can accept any number of channels, so we need to resize channel-dependent
+        // data structures accordinly
+        if self.stft.num_channels() != bus_config.num_output_channels as usize {
+            self.stft = util::StftHelper::new(self.stft.num_channels(), MAX_WINDOW_SIZE, 0);
+        }
+
+        // Planning with RustFFT is very fast, but it will still allocate we we'll plan all of the
+        // FFTs we might need in advance
+        if self.plan_for_order.is_none() {
+            let mut planner = RealFftPlanner::new();
+            let plan_for_order: Vec<Plan> = (MIN_WINDOW_ORDER..=MAX_WINDOW_ORDER)
+                .map(|order| Plan {
+                    r2c_plan: planner.plan_fft_forward(1 << order),
+                    c2r_plan: planner.plan_fft_inverse(1 << order),
+                })
+                .collect();
+            self.plan_for_order = Some(
+                plan_for_order
+                    .try_into()
+                    .unwrap_or_else(|_| panic!("Mismatched plan orders")),
+            );
+        }
+
+        // TODO: Fetch from a parameter
+        let window_size = DEFAULT_WINDOW_SIZE;
+        self.resize_for_window(window_size);
+        context.set_latency_samples(self.stft.latency_samples());
+
+        true
+    }
+
     fn process(
         &mut self,
-        _buffer: &mut Buffer,
+        buffer: &mut Buffer,
         _aux: &mut AuxiliaryBuffers,
-        _context: &mut impl ProcessContext,
+        context: &mut impl ProcessContext,
     ) -> ProcessStatus {
+        // If the window size has changed since the last process call, reset the buffers and chance
+        // our latency. All of these buffers already have enough capacity so this won't allocate.
+        // TODO: Fetch from a parameter
+        let overlap_times = DEFAULT_OVERLAP_TIMES;
+        // TODO: Fetch from a parameter
+        let window_size = DEFAULT_WINDOW_SIZE;
+        if self.window_function.len() != window_size {
+            self.resize_for_window(window_size);
+            context.set_latency_samples(self.stft.latency_samples());
+        }
+
+        // These plans have already been made during initialization we can switch between versions
+        // without reallocating
+        let fft_plan = &mut self.plan_for_order.as_mut().unwrap()
+            // FIXME: Use the parameter
+            // [self.params.window_size_order.value as usize - MIN_WINDOW_ORDER];
+            [DEFAULT_WINDOW_ORDER - MIN_WINDOW_ORDER];
+
+        // The overlap gain compensation is based on a squared Hann window, which will sum perfectly
+        // at four times overlap or higher. We'll apply a regular Hann window before the analysis
+        // and after the synthesis.
+        let gain_compensation: f32 =
+            ((overlap_times as f32 / 4.0) * 1.5).recip() / window_size as f32;
+
+        // We'll apply the square root of the total gain compensation at the DFT and the IDFT
+        // stages. That way the compressor threshold values make much more sense.
+        let input_gain =
+            util::db_to_gain(self.params.input_gain_db.value) * gain_compensation.sqrt();
+        let output_gain =
+            util::db_to_gain(self.params.output_gain_db.value) * gain_compensation.sqrt();
+        // TODO: Mix in the dry signal
+
+        self.stft
+            .process_overlap_add(buffer, overlap_times, |_channel_idx, real_fft_buffer| {
+                // We'll window the input with a Hann function to avoid spectral leakage. The input
+                // gain here also contains a compensation factor for the forward FFT to make the
+                // compressor thresholds make more sense.
+                for (sample, window_sample) in real_fft_buffer.iter_mut().zip(&self.window_function)
+                {
+                    *sample *= window_sample * input_gain;
+                }
+
+                // RustFFT doesn't actually need a scratch buffer here, so we'll pass an empty
+                // buffer instead
+                fft_plan
+                    .r2c_plan
+                    .process_with_scratch(real_fft_buffer, &mut self.complex_fft_buffer, &mut [])
+                    .unwrap();
+
                 // TODO: Do the thing
+
+                // Inverse FFT back into the scratch buffer. This will be added to a ring buffer
+                // which gets written back to the host at a one block delay.
+                fft_plan
+                    .c2r_plan
+                    .process_with_scratch(&mut self.complex_fft_buffer, real_fft_buffer, &mut [])
+                    .unwrap();
+
+                // Apply the window function once more to reduce time domain aliasing. The gain
+                // compensation compensates for the squared Hann window that would be applied if we
+                // didn't do any processing at all as well as the FFT+IFFT itself.
+                for (sample, window_sample) in real_fft_buffer.iter_mut().zip(&self.window_function)
+                {
+                    *sample *= window_sample * output_gain;
+                }
+            });
+
         ProcessStatus::Normal
     }
 }
 
+impl SpectralCompressor {
+    /// `window_size` should not exceed `MAX_WINDOW_SIZE` or this will allocate.
+    fn resize_for_window(&mut self, window_size: usize) {
+        // The FFT algorithms for this window size have already been planned in
+        // `self.plan_for_order`, and all of these data structures already have enough capacity, so
+        // we just need to change some sizes.
+        self.stft.set_block_size(window_size);
+        self.window_function.resize(window_size, 0.0);
+        util::window::hann_in_place(&mut self.window_function);
+        self.complex_fft_buffer
+            .resize(window_size / 2 + 1, Complex32::default());
+    }
+}
+
 impl ClapPlugin for SpectralCompressor {
     const CLAP_ID: &'static str = "nl.robbertvanderhelm.spectral-compressor";
     const CLAP_DESCRIPTION: Option<&'static str> = Some("Turn things into pink noise on demand");

src/util/stft.rs

@@ -245,6 +245,16 @@ impl<const NUM_SIDECHAIN_INPUTS: usize> StftHelper<NUM_SIDECHAIN_INPUTS> {
         self.current_pos = 0;
     }
 
+    /// The number of channels this `StftHelper` was configured for
+    pub fn num_channels(&self) -> usize {
+        self.main_input_ring_buffers.len()
+    }
+
+    /// The maximum block size supported by this `StftHelper`.
+    pub fn max_block_size(&self) -> usize {
+        self.main_input_ring_buffers.capacity()
+    }
+
     /// The amount of latency introduced when processing audio throug hthis [`StftHelper`].
     pub fn latency_samples(&self) -> u32 {
         self.main_input_ring_buffers[0].len() as u32