nih-plug/plugins/spectral_compressor/src/lib.rs

// Spectral Compressor: an FFT based compressor
// Copyright (C) 2021-2022 Robbert van der Helm
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program.  If not, see <https://www.gnu.org/licenses/>.

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>,
}

/// 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()),
        }
    }
}

impl Plugin for SpectralCompressor {
    const NAME: &'static str = "Spectral Compressor";
    const VENDOR: &'static str = "Robbert van der Helm";
    const URL: &'static str = "https://github.com/robbert-vdh/nih-plug";
    const EMAIL: &'static str = "mail@robbertvanderhelm.nl";

    const VERSION: &'static str = "0.2.0";

    const DEFAULT_NUM_INPUTS: u32 = 2;
    const DEFAULT_NUM_OUTPUTS: u32 = 2;

    const SAMPLE_ACCURATE_AUTOMATION: bool = true;

    fn params(&self) -> Arc<dyn Params> {
        self.params.clone()
    }

    fn editor(&self) -> Option<Box<dyn Editor>> {
        editor::create(self.params.clone(), self.editor_state.clone())
    }

    fn accepts_bus_config(&self, config: &BusConfig) -> bool {
        // We can support any channel layout
        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,
        _aux: &mut AuxiliaryBuffers,
        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");
    const CLAP_MANUAL_URL: Option<&'static str> = Some(Self::URL);
    const CLAP_SUPPORT_URL: Option<&'static str> = None;
    const CLAP_FEATURES: &'static [ClapFeature] = &[
        ClapFeature::AudioEffect,
        ClapFeature::Stereo,
        ClapFeature::PhaseVocoder,
        ClapFeature::Compressor,
        ClapFeature::Custom("spectral"),
        ClapFeature::Custom("sosig"),
    ];
}

impl Vst3Plugin for SpectralCompressor {
    const VST3_CLASS_ID: [u8; 16] = *b"SpectrlComprRvdH";
    const VST3_CATEGORIES: &'static str = "Fx|Dynamics|Spectral";
}

nih_export_clap!(SpectralCompressor);
nih_export_vst3!(SpectralCompressor);