firewheel_nodes/

svf.rs

use core::ops::Range;

use firewheel_core::node::NodeError;
use firewheel_core::{
    StreamInfo,
    channel_config::{ChannelConfig, ChannelCount},
    diff::{Diff, Patch},
    dsp::{
        coeff_update::{CoeffUpdateFactor, CoeffUpdateMask},
        filter::{
            butterworth::Q_BUTTERWORTH_ORD2,
            smoothing_filter::DEFAULT_SMOOTH_SECONDS,
            svf::{SvfCoeff, SvfCoeffSimd, SvfStateSimd},
        },
        volume::{Volume, db_to_amp},
    },
    event::ProcEvents,
    node::{
        AudioNode, AudioNodeInfo, AudioNodeProcessor, ConstructProcessorContext, ProcBuffers,
        ProcExtra, ProcInfo, ProcStreamCtx, ProcessStatus,
    },
    param::smoother::{SmoothedParam, SmootherConfig},
};

pub const DEFAULT_Q: f32 = Q_BUTTERWORTH_ORD2;
pub const DEFAULT_MIN_HZ: f32 = 20.0;
pub const DEFAULT_MAX_HZ: f32 = 20_480.0;
pub const DEFAULT_MIN_Q: f32 = 0.02;
pub const DEFAULT_MAX_Q: f32 = 40.0;
pub const DEFAULT_MIN_GAIN_DB: f32 = -24.0;
pub const DEFAULT_MAX_GAIN_DB: f32 = 24.0;

/// The configuration for an [`SvfNode`]
#[derive(Debug, Clone, PartialEq)]
#[cfg_attr(feature = "bevy", derive(bevy_ecs::prelude::Component))]
#[cfg_attr(feature = "bevy_reflect", derive(bevy_reflect::Reflect))]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub struct SvfNodeConfig {
    /// The minimum and maximum values for cutoff frequency in hertz.
    ///
    /// By default this is set to `20.0..20480.0`.
    ///
    /// It is generally not recommended to increase this range
    /// unless you know what you are doing.
    pub freq_range: Range<f32>,

    /// The minimum and maximum values for q values.
    ///
    /// By default this is set to `0.02..40.0`.
    ///
    /// It is generally not recommended to increase this range
    /// unless you know what you are doing.
    pub q_range: Range<f32>,

    /// The minimum and maximum values for filter gain (in decibels).
    ///
    /// By default this is set to `-24.0..24.0`.
    ///
    /// It is generally not recommended to increase this range
    /// unless you know what you are doing.
    pub gain_db_range: Range<f32>,
}

impl Default for SvfNodeConfig {
    fn default() -> Self {
        Self {
            freq_range: DEFAULT_MIN_HZ..DEFAULT_MAX_HZ,
            q_range: DEFAULT_MIN_Q..DEFAULT_MAX_Q,
            gain_db_range: DEFAULT_MIN_GAIN_DB..DEFAULT_MAX_GAIN_DB,
        }
    }
}

/// The filter type to use for an [`SvfNode`]
#[derive(Default, Diff, Patch, Debug, Clone, Copy, PartialEq, Eq)]
#[cfg_attr(feature = "bevy_reflect", derive(bevy_reflect::Reflect))]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
pub enum SvfType {
    // Lowpass (-12 dB per octave)
    #[default]
    Lowpass,
    // Lowpass (-24 dB per octave)
    LowpassX2,
    // Lowpass (-12 dB per octave)
    Highpass,
    // Lowpass (-24 dB per octave)
    HighpassX2,
    // Bandpass (-12 dB per octave)
    Bandpass,
    LowShelf,
    HighShelf,
    Bell,
    Notch,
    Allpass,
}

pub type SvfMonoNode = SvfNode<1>;
pub type SvfStereoNode = SvfNode<2>;

/// An SVF (state variable filter) node
///
/// This is based on the filter model developed by Andrew Simper:
/// <https://cytomic.com/files/dsp/SvfLinearTrapOptimised2.pdf>
#[cfg_attr(feature = "bevy", derive(bevy_ecs::prelude::Component))]
#[cfg_attr(feature = "bevy_reflect", derive(bevy_reflect::Reflect))]
#[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
#[derive(Diff, Patch, Debug, Clone, Copy, PartialEq)]
pub struct SvfNode<const CHANNELS: usize = 2> {
    /// The type of filter
    pub filter_type: SvfType,

    /// The cutoff frequency in hertz in the range `[20.0, 20480.0]`.
    pub cutoff_hz: f32,
    /// The quality (q) factor
    ///
    /// This is also sometimes referred to as "bandwidth", but note the
    /// formula to convert bandwidth in hertz to q is:
    ///
    /// `Q = cutoff_hz / BW`
    ///
    /// and the formula to convert bandwidth in octaves to q is:
    ///
    /// `Q = sqrt(2^BW) / (2^BW - 1)`
    pub q_factor: f32,
    /// The filter gain
    ///
    /// This only has effect if the filter type is one of the following:
    /// * [`SvfType::LowShelf`]
    /// * [`SvfType::HighShelf`]
    /// * [`SvfType::Bell`]
    pub gain: Volume,

    /// The time in seconds of the internal smoothing filter.
    ///
    /// By default this is set to `0.062` (62ms). This value is chosen such that
    /// the stair-stepping effect isn't noticeable for a typical block size of 1024
    /// samples.
    pub smooth_seconds: f32,

    /// An exponent representing the rate at which DSP coefficients are
    /// updated when parameters are being smoothed.
    ///
    /// Smaller values will produce less "stair-stepping" artifacts,
    /// but will also consume more CPU.
    ///
    /// The resulting number of frames (samples in a single channel of audio)
    /// that will elapse between each update is calculated as
    /// `2^coeff_update_factor`.
    ///
    /// By default this is set to `4`.
    pub coeff_update_factor: CoeffUpdateFactor,
}

impl<const CHANNELS: usize> Default for SvfNode<CHANNELS> {
    fn default() -> Self {
        Self {
            filter_type: SvfType::Lowpass,
            cutoff_hz: 1_000.0,
            q_factor: DEFAULT_Q,
            gain: Volume::Decibels(0.0),
            smooth_seconds: DEFAULT_SMOOTH_SECONDS,
            coeff_update_factor: CoeffUpdateFactor::default(),
        }
    }
}

impl<const CHANNELS: usize> SvfNode<CHANNELS> {
    /// Construct a new SVF node with the lowpass filter type of order 2.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    /// * `enabled` - Whether or not this node is enabled
    pub const fn from_lowpass(cutoff_hz: f32, q_factor: f32) -> Self {
        Self {
            filter_type: SvfType::Lowpass,
            cutoff_hz,
            q_factor,
            gain: Volume::UNITY_GAIN,
            smooth_seconds: DEFAULT_SMOOTH_SECONDS,
            coeff_update_factor: CoeffUpdateFactor(5),
        }
    }

    /// Construct a new SVF node with the lowpass filter type of order 4.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    /// * `enabled` - Whether or not this node is enabled
    pub const fn from_lowpass_x2(cutoff_hz: f32, q_factor: f32) -> Self {
        Self {
            filter_type: SvfType::LowpassX2,
            cutoff_hz,
            q_factor,
            gain: Volume::UNITY_GAIN,
            smooth_seconds: DEFAULT_SMOOTH_SECONDS,
            coeff_update_factor: CoeffUpdateFactor(5),
        }
    }

    /// Construct a new SVF node with the highpass filter type of order 2.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    /// * `enabled` - Whether or not this node is enabled
    pub const fn from_highpass(cutoff_hz: f32, q_factor: f32) -> Self {
        Self {
            filter_type: SvfType::Highpass,
            cutoff_hz,
            q_factor,
            gain: Volume::UNITY_GAIN,
            smooth_seconds: DEFAULT_SMOOTH_SECONDS,
            coeff_update_factor: CoeffUpdateFactor(5),
        }
    }

    /// Construct a new SVF node with the highpass filter type of order 4.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    /// * `enabled` - Whether or not this node is enabled
    pub const fn from_highpass_x2(cutoff_hz: f32, q_factor: f32) -> Self {
        Self {
            filter_type: SvfType::HighpassX2,
            cutoff_hz,
            q_factor,
            gain: Volume::UNITY_GAIN,
            smooth_seconds: DEFAULT_SMOOTH_SECONDS,
            coeff_update_factor: CoeffUpdateFactor(5),
        }
    }

    /// Construct a new SVF node with the bandpass filter type.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    /// * `enabled` - Whether or not this node is enabled
    pub const fn from_bandpass(cutoff_hz: f32, q_factor: f32) -> Self {
        Self {
            filter_type: SvfType::Bandpass,
            cutoff_hz,
            q_factor,
            gain: Volume::UNITY_GAIN,
            smooth_seconds: DEFAULT_SMOOTH_SECONDS,
            coeff_update_factor: CoeffUpdateFactor(5),
        }
    }

    /// Construct a new SVF node with the lowshelf filter type.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `gain` - The filter gain
    /// * `q_factor` - The quality (q) factor
    /// * `enabled` - Whether or not this node is enabled
    pub const fn from_lowshelf(cutoff_hz: f32, gain: Volume, q_factor: f32) -> Self {
        Self {
            filter_type: SvfType::LowShelf,
            cutoff_hz,
            q_factor,
            gain,
            smooth_seconds: DEFAULT_SMOOTH_SECONDS,
            coeff_update_factor: CoeffUpdateFactor(5),
        }
    }

    /// Construct a new SVF node with the highshelf filter type.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `gain` - The filter gain
    /// * `q_factor` - The quality (q) factor
    /// * `enabled` - Whether or not this node is enabled
    pub const fn from_highshelf(cutoff_hz: f32, gain: Volume, q_factor: f32) -> Self {
        Self {
            filter_type: SvfType::HighShelf,
            cutoff_hz,
            q_factor,
            gain,
            smooth_seconds: DEFAULT_SMOOTH_SECONDS,
            coeff_update_factor: CoeffUpdateFactor(5),
        }
    }

    /// Construct a new SVF node with the bell filter type.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `gain` - The filter gain
    /// * `q_factor` - The quality (q) factor
    /// * `enabled` - Whether or not this node is enabled
    pub const fn from_bell(cutoff_hz: f32, gain: Volume, q_factor: f32) -> Self {
        Self {
            filter_type: SvfType::Bell,
            cutoff_hz,
            q_factor,
            gain,
            smooth_seconds: DEFAULT_SMOOTH_SECONDS,
            coeff_update_factor: CoeffUpdateFactor(5),
        }
    }

    /// Construct a new SVF node with the notch filter type.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    /// * `enabled` - Whether or not this node is enabled
    pub const fn from_notch(cutoff_hz: f32, q_factor: f32) -> Self {
        Self {
            filter_type: SvfType::Notch,
            cutoff_hz,
            q_factor,
            gain: Volume::UNITY_GAIN,
            smooth_seconds: DEFAULT_SMOOTH_SECONDS,
            coeff_update_factor: CoeffUpdateFactor(5),
        }
    }

    /// Construct a new SVF node with the allpass filter type.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    /// * `enabled` - Whether or not this node is enabled
    pub const fn from_allpass(cutoff_hz: f32, q_factor: f32) -> Self {
        Self {
            filter_type: SvfType::Allpass,
            cutoff_hz,
            q_factor,
            gain: Volume::UNITY_GAIN,
            smooth_seconds: DEFAULT_SMOOTH_SECONDS,
            coeff_update_factor: CoeffUpdateFactor(5),
        }
    }

    /// Set the parameters to use a lowpass filter type of order 2.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    pub const fn set_lowpass(&mut self, cutoff_hz: f32, q_factor: f32) {
        self.filter_type = SvfType::Lowpass;
        self.cutoff_hz = cutoff_hz;
        self.q_factor = q_factor;
    }

    /// Set the parameters to use a lowpass filter type of order 4.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    pub const fn set_lowpass_x2(&mut self, cutoff_hz: f32, q_factor: f32) {
        self.filter_type = SvfType::LowpassX2;
        self.cutoff_hz = cutoff_hz;
        self.q_factor = q_factor;
    }

    /// Set the parameters to use a highpass filter type of order 2.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    pub const fn set_highpass(&mut self, cutoff_hz: f32, q_factor: f32) {
        self.filter_type = SvfType::Highpass;
        self.cutoff_hz = cutoff_hz;
        self.q_factor = q_factor;
    }

    /// Set the parameters to use a highpass filter type of order 4.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    pub const fn set_highpass_x2(&mut self, cutoff_hz: f32, q_factor: f32) {
        self.filter_type = SvfType::HighpassX2;
        self.cutoff_hz = cutoff_hz;
        self.q_factor = q_factor;
    }

    /// Set the parameters to use a bandpass filter type.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    pub const fn set_bandpass(&mut self, cutoff_hz: f32, q_factor: f32) {
        self.filter_type = SvfType::Bandpass;
        self.cutoff_hz = cutoff_hz;
        self.q_factor = q_factor;
    }

    /// Set the parameters to use a lowshelf filter type.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `gain` - The filter gain
    /// * `q_factor` - The quality (q) factor
    pub const fn set_lowshelf(&mut self, cutoff_hz: f32, gain: Volume, q_factor: f32) {
        self.filter_type = SvfType::LowShelf;
        self.cutoff_hz = cutoff_hz;
        self.gain = gain;
        self.q_factor = q_factor;
    }

    /// Set the parameters to use a highshelf filter type.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `gain` - The filter gain
    /// * `q_factor` - The quality (q) factor
    pub const fn set_highshelf(&mut self, cutoff_hz: f32, gain: Volume, q_factor: f32) {
        self.filter_type = SvfType::HighShelf;
        self.cutoff_hz = cutoff_hz;
        self.gain = gain;
        self.q_factor = q_factor;
    }

    /// Set the parameters to use a bell filter type.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `gain` - The filter gain
    /// * `q_factor` - The quality (q) factor
    pub const fn set_bell(&mut self, cutoff_hz: f32, gain: Volume, q_factor: f32) {
        self.filter_type = SvfType::Bell;
        self.cutoff_hz = cutoff_hz;
        self.gain = gain;
        self.q_factor = q_factor;
    }

    /// Set the parameters to use a notch filter type.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    pub const fn set_notch(&mut self, cutoff_hz: f32, q_factor: f32) {
        self.filter_type = SvfType::Notch;
        self.cutoff_hz = cutoff_hz;
        self.q_factor = q_factor;
    }

    /// Set the parameters to use an allpass filter type.
    ///
    /// * `cutoff_hz` - The cutoff frequency in hertz in the range `[20.0, 20480.0]`
    /// * `q_factor` - The quality (q) factor
    pub const fn set_allpass(&mut self, cutoff_hz: f32, q_factor: f32) {
        self.filter_type = SvfType::Allpass;
        self.cutoff_hz = cutoff_hz;
        self.q_factor = q_factor;
    }

    /// Set the given filter gain in a linear scale, where `0.0` is silence and
    /// `1.0` is unity gain.
    ///
    /// These units are suitable for volume sliders (simply convert percent
    /// volume to linear volume by diving the percent volume by 100).
    ///
    /// This only has effect if the filter type is one of the following:
    /// * [`SvfType::LowShelf`]
    /// * [`SvfType::HighShelf`]
    /// * [`SvfType::Bell`]
    pub const fn set_gain_linear(&mut self, linear: f32) {
        self.gain = Volume::Linear(linear);
    }

    /// Set the given filter gain in decibels, where `0.0` is unity gain and
    /// `f32::NEG_INFINITY` is silence.
    ///
    /// This only has effect if the filter type is one of the following:
    /// * [`SvfType::LowShelf`]
    /// * [`SvfType::HighShelf`]
    /// * [`SvfType::Bell`]
    pub const fn set_gain_decibels(&mut self, decibels: f32) {
        self.gain = Volume::Decibels(decibels);
    }
}

impl<const CHANNELS: usize> AudioNode for SvfNode<CHANNELS> {
    type Configuration = SvfNodeConfig;

    fn info(&self, _config: &Self::Configuration) -> Result<AudioNodeInfo, NodeError> {
        Ok(AudioNodeInfo::new()
            .debug_name("svf")
            .channel_config(ChannelConfig {
                num_inputs: ChannelCount::new(CHANNELS as u32).unwrap(),
                num_outputs: ChannelCount::new(CHANNELS as u32).unwrap(),
            })
            // Use SVF node as a test for in-place buffers, even though the
            // schedulder does not natively support this yet, meaning it does
            // not improve performance yet.
            .in_place_buffers(true))
    }

    fn construct_processor(
        &self,
        config: &Self::Configuration,
        cx: ConstructProcessorContext,
    ) -> Result<impl AudioNodeProcessor, NodeError> {
        let cutoff_hz = self
            .cutoff_hz
            .clamp(config.freq_range.start, config.freq_range.end);
        let q_factor = self
            .q_factor
            .clamp(config.q_range.start, config.q_range.end);

        let min_gain = db_to_amp(config.gain_db_range.start);
        let max_gain = db_to_amp(config.gain_db_range.end);
        let mut gain = self.gain.amp().clamp(min_gain, max_gain);
        if gain > 0.99999 && gain < 1.00001 {
            gain = 1.0;
        }

        let mut new_self = Processor {
            filter_0: SvfStateSimd::<CHANNELS>::default(),
            filter_1: SvfStateSimd::<CHANNELS>::default(),
            num_filters: 0,
            filter_0_coeff: SvfCoeffSimd::<CHANNELS>::default(),
            filter_1_coeff: SvfCoeffSimd::<CHANNELS>::default(),
            filter_type: self.filter_type,
            cutoff_hz: SmoothedParam::new(
                cutoff_hz,
                config.freq_range.end - config.freq_range.start,
                SmootherConfig {
                    smooth_seconds: self.smooth_seconds,
                    ..Default::default()
                },
                cx.stream_info.sample_rate,
            ),
            q_factor: SmoothedParam::new(
                q_factor,
                config.q_range.end - config.q_range.start,
                SmootherConfig {
                    smooth_seconds: self.smooth_seconds,
                    ..Default::default()
                },
                cx.stream_info.sample_rate,
            ),
            gain: SmoothedParam::new(
                gain,
                max_gain - min_gain,
                SmootherConfig {
                    smooth_seconds: self.smooth_seconds,
                    ..Default::default()
                },
                cx.stream_info.sample_rate,
            ),
            freq_range: config.freq_range.clone(),
            q_range: config.q_range.clone(),
            gain_range: min_gain..max_gain,
            coeff_update_mask: self.coeff_update_factor.mask(),
            params_changed: false,
        };

        new_self.update_coefficients(
            new_self.cutoff_hz.target_value(),
            new_self.q_factor.target_value(),
            new_self.gain.target_value(),
            cx.stream_info.sample_rate_recip as f32,
        );

        Ok(new_self)
    }
}

struct Processor<const CHANNELS: usize> {
    filter_0: SvfStateSimd<CHANNELS>,
    filter_1: SvfStateSimd<CHANNELS>,
    num_filters: usize,

    filter_0_coeff: SvfCoeffSimd<CHANNELS>,
    filter_1_coeff: SvfCoeffSimd<CHANNELS>,

    filter_type: SvfType,
    cutoff_hz: SmoothedParam,
    q_factor: SmoothedParam,
    gain: SmoothedParam,

    freq_range: Range<f32>,
    q_range: Range<f32>,
    gain_range: Range<f32>,
    coeff_update_mask: CoeffUpdateMask,
    params_changed: bool,
}

impl<const CHANNELS: usize> Processor<CHANNELS> {
    #[cold]
    #[inline(never)]
    fn update_coefficients(&mut self, cutoff_hz: f32, q: f32, gain: f32, sample_rate_recip: f32) {
        match self.filter_type {
            SvfType::Lowpass => {
                self.num_filters = 1;

                self.filter_0_coeff =
                    SvfCoeffSimd::splat(SvfCoeff::lowpass_ord2(cutoff_hz, q, sample_rate_recip));
            }
            SvfType::LowpassX2 => {
                self.num_filters = 2;

                let [coeff_0, coeff_1] = SvfCoeff::lowpass_ord4(cutoff_hz, q, sample_rate_recip);
                self.filter_0_coeff = SvfCoeffSimd::splat(coeff_0);
                self.filter_1_coeff = SvfCoeffSimd::splat(coeff_1);
            }
            SvfType::Highpass => {
                self.num_filters = 1;

                self.filter_0_coeff =
                    SvfCoeffSimd::splat(SvfCoeff::highpass_ord2(cutoff_hz, q, sample_rate_recip));
            }
            SvfType::HighpassX2 => {
                self.num_filters = 2;

                let [coeff_0, coeff_1] = SvfCoeff::highpass_ord4(cutoff_hz, q, sample_rate_recip);
                self.filter_0_coeff = SvfCoeffSimd::splat(coeff_0);
                self.filter_1_coeff = SvfCoeffSimd::splat(coeff_1);
            }
            SvfType::Bandpass => {
                self.num_filters = 2;

                self.filter_0_coeff =
                    SvfCoeffSimd::splat(SvfCoeff::lowpass_ord2(cutoff_hz, q, sample_rate_recip));
                self.filter_1_coeff =
                    SvfCoeffSimd::splat(SvfCoeff::highpass_ord2(cutoff_hz, q, sample_rate_recip));
            }
            SvfType::LowShelf => {
                self.num_filters = 1;

                self.filter_0_coeff =
                    SvfCoeffSimd::splat(SvfCoeff::low_shelf(cutoff_hz, q, gain, sample_rate_recip));
            }
            SvfType::HighShelf => {
                self.num_filters = 1;

                self.filter_0_coeff = SvfCoeffSimd::splat(SvfCoeff::high_shelf(
                    cutoff_hz,
                    q,
                    gain,
                    sample_rate_recip,
                ));
            }
            SvfType::Bell => {
                self.num_filters = 1;

                self.filter_0_coeff =
                    SvfCoeffSimd::splat(SvfCoeff::bell(cutoff_hz, q, gain, sample_rate_recip));
            }
            SvfType::Notch => {
                self.num_filters = 1;

                self.filter_0_coeff =
                    SvfCoeffSimd::splat(SvfCoeff::notch(cutoff_hz, q, sample_rate_recip));
            }
            SvfType::Allpass => {
                self.num_filters = 1;

                self.filter_0_coeff =
                    SvfCoeffSimd::splat(SvfCoeff::allpass(cutoff_hz, q, sample_rate_recip));
            }
        }

        if self.num_filters == 1 {
            self.filter_1.reset();
        }
    }

    /// Smoothing loop for single-filter types that don't use gain
    /// (Lowpass, Highpass, Notch, Allpass).
    fn smoothing_loop_single(&mut self, info: &ProcInfo, outputs: &mut [&mut [f32]]) {
        assert!(outputs.len() == CHANNELS);
        for ch in outputs.iter() {
            assert!(ch.len() >= info.frames);
        }

        for i in 0..info.frames {
            let cutoff_hz = self.cutoff_hz.next_smoothed();
            let q = self.q_factor.next_smoothed();

            // Only recalculate coefficients every 2^coeff_update_factor frames
            if self.coeff_update_mask.do_update(i) {
                self.update_coefficients(cutoff_hz, q, 0.0, info.sample_rate_recip as f32);
            }

            let s: [f32; CHANNELS] = core::array::from_fn(|ch_i| {
                // Safety: These bounds have been checked above.
                unsafe { *outputs.get_unchecked(ch_i).get_unchecked(i) }
            });

            let out = self.filter_0.process(s, &self.filter_0_coeff);

            for (ch_i, &o) in out.iter().enumerate().take(CHANNELS) {
                // Safety: These bounds have been checked above.
                unsafe {
                    *outputs.get_unchecked_mut(ch_i).get_unchecked_mut(i) = o;
                }
            }
        }
    }

    /// Smoothing loop for single-filter types that use gain
    /// (LowShelf, HighShelf, Bell).
    fn smoothing_loop_single_with_gain(&mut self, info: &ProcInfo, outputs: &mut [&mut [f32]]) {
        assert!(outputs.len() == CHANNELS);
        for ch in outputs.iter() {
            assert!(ch.len() >= info.frames);
        }

        for i in 0..info.frames {
            let cutoff_hz = self.cutoff_hz.next_smoothed();
            let q = self.q_factor.next_smoothed();
            let gain = self.gain.next_smoothed();

            // Only recalculate coefficients every 2^coeff_update_factor frames
            if self.coeff_update_mask.do_update(i) {
                self.update_coefficients(cutoff_hz, q, gain, info.sample_rate_recip as f32);
            }

            let s: [f32; CHANNELS] = core::array::from_fn(|ch_i| {
                // Safety: These bounds have been checked above.
                unsafe { *outputs.get_unchecked(ch_i).get_unchecked(i) }
            });

            let out = self.filter_0.process(s, &self.filter_0_coeff);

            for (ch_i, &o) in out.iter().enumerate().take(CHANNELS) {
                // Safety: These bounds have been checked above.
                unsafe {
                    *outputs.get_unchecked_mut(ch_i).get_unchecked_mut(i) = o;
                }
            }
        }
    }

    /// Smoothing loop for dual-filter types that don't use gain
    /// (LowpassX2, HighpassX2, Bandpass).
    fn smoothing_loop_dual(&mut self, info: &ProcInfo, outputs: &mut [&mut [f32]]) {
        assert!(outputs.len() == CHANNELS);
        for ch in outputs.iter() {
            assert!(ch.len() >= info.frames);
        }

        for i in 0..info.frames {
            let cutoff_hz = self.cutoff_hz.next_smoothed();
            let q = self.q_factor.next_smoothed();

            // Only recalculate coefficients every 2^coeff_update_factor frames
            if self.coeff_update_mask.do_update(i) {
                self.update_coefficients(cutoff_hz, q, 0.0, info.sample_rate_recip as f32);
            }

            let s: [f32; CHANNELS] = core::array::from_fn(|ch_i| {
                // Safety: These bounds have been checked above.
                unsafe { *outputs.get_unchecked(ch_i).get_unchecked(i) }
            });

            let s = self.filter_0.process(s, &self.filter_0_coeff);
            let out = self.filter_1.process(s, &self.filter_1_coeff);

            for (ch_i, &o) in out.iter().enumerate().take(CHANNELS) {
                // Safety: These bounds have been checked above.
                unsafe {
                    *outputs.get_unchecked_mut(ch_i).get_unchecked_mut(i) = o;
                }
            }
        }
    }
}

impl<const CHANNELS: usize> Processor<CHANNELS> {
    fn reset(&mut self) {
        self.cutoff_hz.reset_to_target();
        self.filter_0.reset();
        self.filter_1.reset();
    }
}

impl<const CHANNELS: usize> AudioNodeProcessor for Processor<CHANNELS> {
    fn events(&mut self, info: &ProcInfo, events: &mut ProcEvents, _extra: &mut ProcExtra) {
        for patch in events.drain_patches::<SvfNode<CHANNELS>>() {
            match patch {
                SvfNodePatch::FilterType(filter_type) => {
                    self.params_changed = true;
                    self.filter_type = filter_type;
                }
                SvfNodePatch::CutoffHz(cutoff) => {
                    self.params_changed = true;
                    self.cutoff_hz
                        .set_value(cutoff.clamp(self.freq_range.start, self.freq_range.end));
                }
                SvfNodePatch::QFactor(q_factor) => {
                    self.params_changed = true;
                    self.q_factor
                        .set_value(q_factor.clamp(self.q_range.start, self.q_range.end));
                }
                SvfNodePatch::Gain(gain) => {
                    self.params_changed = true;
                    let mut gain = gain.amp().clamp(self.gain_range.start, self.gain_range.end);
                    if gain > 0.99999 && gain < 1.00001 {
                        gain = 1.0;
                    }
                    self.gain.set_value(gain);
                }
                SvfNodePatch::SmoothSeconds(seconds) => {
                    self.cutoff_hz.set_smooth_seconds(seconds, info.sample_rate);
                }
                SvfNodePatch::CoeffUpdateFactor(f) => {
                    self.coeff_update_mask = f.mask();
                }
            }
        }
    }

    fn bypassed(&mut self, _bypassed: bool) {
        self.reset();
    }

    fn process(
        &mut self,
        info: &ProcInfo,
        buffers: ProcBuffers,
        _extra: &mut ProcExtra,
    ) -> ProcessStatus {
        // Make sure that in-place buffer processing is being handled correctly.
        debug_assert_eq!(buffers.inputs.len(), 0);

        if info.out_silence_mask.all_channels_silent(CHANNELS) {
            // Outputs will be silent, so no need to process.

            // Reset the smoothers and filters since they don't need to smooth any
            // output.
            self.reset();

            return ProcessStatus::ClearAllOutputs;
        }

        if self.cutoff_hz.is_smoothing() || self.q_factor.is_smoothing() || self.gain.is_smoothing()
        {
            match self.filter_type {
                SvfType::Lowpass | SvfType::Highpass | SvfType::Notch | SvfType::Allpass => {
                    self.smoothing_loop_single(info, buffers.outputs)
                }
                SvfType::LowShelf | SvfType::HighShelf | SvfType::Bell => {
                    self.smoothing_loop_single_with_gain(info, buffers.outputs)
                }
                SvfType::LowpassX2 | SvfType::HighpassX2 | SvfType::Bandpass => {
                    self.smoothing_loop_dual(info, buffers.outputs)
                }
            }

            if self.cutoff_hz.settle() && self.q_factor.settle() && self.gain.settle() {
                self.update_coefficients(
                    self.cutoff_hz.target_value(),
                    self.q_factor.target_value(),
                    self.gain.target_value(),
                    info.sample_rate_recip as f32,
                );
            }
        } else {
            // The cutoff parameter is not currently smoothing, so we can optimize by
            // only updating the filter coefficients once.
            if self.params_changed {
                self.params_changed = false;
                self.update_coefficients(
                    self.cutoff_hz.target_value(),
                    self.q_factor.target_value(),
                    self.gain.target_value(),
                    info.sample_rate_recip as f32,
                );
            }

            assert!(buffers.outputs.len() == CHANNELS);
            for ch in buffers.outputs.iter() {
                assert!(ch.len() >= info.frames);
            }

            if self.num_filters == 1 {
                for i in 0..info.frames {
                    let s: [f32; CHANNELS] = core::array::from_fn(|ch_i| {
                        // Safety: These bounds have been checked above.
                        unsafe { *buffers.outputs.get_unchecked(ch_i).get_unchecked(i) }
                    });

                    let out = self.filter_0.process(s, &self.filter_0_coeff);

                    for (ch_i, &o) in out.iter().enumerate().take(CHANNELS) {
                        // Safety: These bounds have been checked above.
                        unsafe {
                            *buffers.outputs.get_unchecked_mut(ch_i).get_unchecked_mut(i) = o;
                        }
                    }
                }
            } else {
                for i in 0..info.frames {
                    let s: [f32; CHANNELS] = core::array::from_fn(|ch_i| {
                        // Safety: These bounds have been checked above.
                        unsafe { *buffers.outputs.get_unchecked(ch_i).get_unchecked(i) }
                    });

                    let s = self.filter_0.process(s, &self.filter_0_coeff);
                    let out = self.filter_1.process(s, &self.filter_1_coeff);

                    for (ch_i, &o) in out.iter().enumerate().take(CHANNELS) {
                        // Safety: These bounds have been checked above.
                        unsafe {
                            *buffers.outputs.get_unchecked_mut(ch_i).get_unchecked_mut(i) = o;
                        }
                    }
                }
            }
        }

        ProcessStatus::OutputsModified
    }

    fn new_stream(&mut self, stream_info: &StreamInfo, _context: &mut ProcStreamCtx) {
        self.cutoff_hz.update_sample_rate(stream_info.sample_rate);
        self.q_factor.update_sample_rate(stream_info.sample_rate);
        self.gain.update_sample_rate(stream_info.sample_rate);

        self.update_coefficients(
            self.cutoff_hz.target_value(),
            self.q_factor.target_value(),
            self.gain.target_value(),
            stream_info.sample_rate_recip as f32,
        );
    }
}