diff --git a/Cargo.toml b/Cargo.toml
index f01e9cc..58655fa 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -24,6 +24,7 @@ hound         = "3.4.0"
 microfft    = "0.3.1"
 num-complex = "0.2"
 jack        = "0.6.6"
+rustfft     = "6.0.0"
 
 [lib]
 path       = "src/lib.rs"
diff --git a/src/dsp/node_sfilter.rs b/src/dsp/node_sfilter.rs
index e3d5cb4..a81ed7f 100644
--- a/src/dsp/node_sfilter.rs
+++ b/src/dsp/node_sfilter.rs
@@ -143,5 +143,7 @@ impl DspNode for SFilter {
             },
             _ => {},
         }
+
+        ctx_vals[0].set(out.read(ctx.nframes() - 1));
     }
 }
diff --git a/tests/common/mod.rs b/tests/common/mod.rs
index 5c92124..16166b9 100644
--- a/tests/common/mod.rs
+++ b/tests/common/mod.rs
@@ -422,6 +422,18 @@ pub fn run_and_get_fft4096(
     fft_thres_at_ms(&mut out_l[..], FFT::F4096, thres, offs_ms)
 }
 
+#[allow(unused)]
+pub fn run_and_get_fft4096_2(
+    node_exec: &mut hexodsp::nodes::NodeExecutor,
+    thres: u32) -> Vec<(u16, u32)>
+{
+    let min_samples_for_fft = 4096.0;
+    let min_len_samples = 2.0 * min_samples_for_fft;
+    let run_len_s = min_len_samples / SAMPLE_RATE;
+    let (mut out_l, _out_r) = run_no_input(node_exec, run_len_s);
+    fft_16k(&mut out_l[..], 4096, thres)
+}
+
 #[allow(unused)]
 pub fn calc_exp_avg_buckets4096(fft: &[(u16, u32)]) -> Vec<(u16, u32)> {
     let mut avg     = vec![];
@@ -592,3 +604,49 @@ pub fn fft_thres_at_ms(buf: &mut [f32], size: FFT, amp_thres: u32, ms_idx: f32)
     res
 }
 
+pub fn fft_16k(buf: &mut [f32], len: usize, amp_thres: u32) -> Vec<(u16, u32)> {
+    let mut res = vec![];
+
+    if len > buf.len() {
+        return res;
+    }
+
+    // Hann window:
+    for (i, s) in buf[0..len].iter_mut().enumerate() {
+        let w =
+            0.5
+            * (1.0 
+               - ((2.0 * std::f32::consts::PI * i as f32)
+                  / (len as f32 - 1.0))
+                 .cos());
+        *s *= w;
+    }
+
+    use rustfft::{FftPlanner, num_complex::Complex};
+
+    let mut complex_buf =
+        buf.iter()
+           .map(|s| Complex { re: *s, im: 0.0 })
+           .collect::<Vec<Complex<f32>>>();
+
+    let mut p = FftPlanner::<f32>::new();
+    let fft = p.plan_fft_forward(len);
+
+    fft.process(&mut complex_buf[0..len]);
+
+    let amplitudes: Vec<_> =
+        complex_buf[0..len].iter().map(|c| c.norm() as u32).collect();
+    println!("fft: {:?}", &complex_buf[0..len]);
+
+    for (i, amp) in amplitudes.iter().enumerate() {
+        if *amp >= amp_thres {
+            let freq = (i as f32 * SAMPLE_RATE) / len as f32;
+            println!("{:6.0} {}", freq, *amp);
+            res.push((freq.round() as u16, *amp));
+        }
+    }
+
+    res
+}
+
+
diff --git a/tests/node_sfilter.rs b/tests/node_sfilter.rs
index 43dfa45..f67b84a 100644
--- a/tests/node_sfilter.rs
+++ b/tests/node_sfilter.rs
@@ -2,7 +2,7 @@ mod common;
 use common::*;
 
 fn setup_sfilter_matrix() -> (Matrix, NodeExecutor) {
-    let (node_conf, mut node_exec) = new_node_engine();
+    let (node_conf, node_exec) = new_node_engine();
     let mut matrix = Matrix::new(node_conf, 3, 3);
 
     let noise = NodeId::Noise(0);
@@ -50,6 +50,16 @@ fn check_node_sfilter_lowpass() {
             (1500, 8), (2000, 4), (3000, 4), (4000, 0), (8000, 0), (12000, 0),
         ]);
 
+//    let v = run_and_get_fft4096_2(&mut node_exec, 1);
+//    assert_eq!(
+//        avg_fft_freqs(4.0, &[
+//            100, 250, 500, 750, 1000, 1500, 2000, 3000, 4000, 8000, 12000, 16000,
+//        ], &v[..]), vec![
+//            (0, 16), (100, 24), (250, 16), (500, 12), (750, 12), (1000, 12),
+//            (1500, 8), (2000, 4), (3000, 4), (4000, 0), (8000, 0), (12000, 0),
+//        ]);
+//    assert!(false);
+
     // Low Pass @ 4000Hz
     let fft = fft_with_freq_res_type(&mut matrix, &mut node_exec, 0, 4000.0, 0.0);
     assert_eq!(