From 3d099f884c2a487b9615a4061924a3c67484cb40 Mon Sep 17 00:00:00 2001
From: Weird Constructor <weirdconstructor@gmail.com>
Date: Sat, 10 Jul 2021 22:34:03 +0200
Subject: [PATCH] added RC filter implementation

---
 src/dsp/mod.rs          |  2 +-
 src/dsp/node_sfilter.rs | 29 ++++++++++++++++++++++++++---
 tests/node_sfilter.rs   |  8 ++++++++
 3 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/src/dsp/mod.rs b/src/dsp/mod.rs
index 0ff1914..26cc353 100644
--- a/src/dsp/mod.rs
+++ b/src/dsp/mod.rs
@@ -582,7 +582,7 @@ macro_rules! node_list {
             sfilter => SFilter UIType::Generic UICategory::Signal
                (0  inp   n_id      d_id  r_id   f_def stp_d -1.0, 1.0, 0.0)
                (1 freq  n_pit      d_pit r_fq  f_freq  stp_d -1.0, 0.5647131, 1000.0)
-               {2 0 ftype setting(0) fa_sfilter_type 0 2}
+               {2 0 ftype setting(0) fa_sfilter_type 0 3}
                [0 sig],
             test => Test UIType::Generic UICategory::IOUtil
                (0 f     n_id      d_id   r_id   f_def stp_d 0.0, 1.0, 0.5)
diff --git a/src/dsp/node_sfilter.rs b/src/dsp/node_sfilter.rs
index 150e86c..bdc7900 100644
--- a/src/dsp/node_sfilter.rs
+++ b/src/dsp/node_sfilter.rs
@@ -9,8 +9,10 @@ use crate::dsp::{NodeId, SAtom, ProcBuf, DspNode, LedPhaseVals, NodeContext};
 macro_rules! fa_sfilter_type { ($formatter: expr, $v: expr, $denorm_v: expr) => { {
     let s =
         match ($v.round() as usize) {
-            0  => "LP(1p)",
-            1  => "HP(1p)",
+            0  => "LPDat(1p)",
+            1  => "LPSVF(1p)",
+            2  => "LPDAFX(1p)",
+            3  => "RC",
             _  => "?",
         };
     write!($formatter, "{}", s)
@@ -21,6 +23,7 @@ macro_rules! fa_sfilter_type { ($formatter: expr, $v: expr, $denorm_v: expr) =>
 pub struct SFilter {
     israte: f64,
     z:      f64,
+    y:      f64,
 }
 
 impl SFilter {
@@ -28,6 +31,7 @@ impl SFilter {
         Self {
             israte: 1.0 / 44100.0,
             z:      0.0,
+            y:      0.0,
         }
     }
     pub const inp : &'static str =
@@ -57,6 +61,7 @@ impl DspNode for SFilter {
     }
     fn reset(&mut self) {
         self.z = 0.0;
+        self.y = 0.0;
     }
 
     #[inline]
@@ -124,7 +129,25 @@ impl DspNode for SFilter {
                     self.z = a * input - b * self.z;
                     out.write(frame, self.z as f32);
                 }
-            }
+            },
+            // From https://en.wikipedia.org/wiki/RC_circuit
+            3 => {
+                for frame in 0..ctx.nframes() {
+                    let input = inp.read(frame) as f64;
+                    let c =
+                        2.0
+                        / (std::f64::consts::TAU
+                         * (denorm::SFilter::freq(freq, frame) as f64)
+                         * self.israte);
+
+                    let y = (input + self.z - self.y * (1.0 - c)) / (1.0 + c);
+                    self.z = input;
+                    self.y = y;
+
+                    // highpass: self.z - self.y
+                    out.write(frame, y as f32);
+                }
+            },
             _ => {},
         }
     }
diff --git a/tests/node_sfilter.rs b/tests/node_sfilter.rs
index d863419..5ba9f68 100644
--- a/tests/node_sfilter.rs
+++ b/tests/node_sfilter.rs
@@ -53,6 +53,14 @@ fn check_node_sfilter_compare() {
     let ta = std::time::Instant::now().duration_since(ta);
     println!("ta3 Elapsed: {:?}", ta);
 
+    pset_s(&mut matrix, sf, "ftype", 3);
+
+    let ta = std::time::Instant::now();
+    let (out_l, _) = run_for_ms(&mut node_exec, 10000.0);
+    save_wav("check_noise_sfilt4.wav", &out_l);
+    let ta = std::time::Instant::now().duration_since(ta);
+    println!("ta4 Elapsed: {:?}", ta);
+
 //    let fft = run_and_get_fft4096(&mut node_exec, 5, 1000.0);
 //    for (fq, lvl) in fft {
 //        println!("{:5}: {}", fq, lvl);