diff --git a/sine.wav b/sine.wav
index 2c038d5..ab39f0a 100644
Binary files a/sine.wav and b/sine.wav differ
diff --git a/src/bfsk.rs b/src/bfsk.rs
index f71b4b3..ebc4feb 100644
--- a/src/bfsk.rs
+++ b/src/bfsk.rs
@@ -46,6 +46,14 @@ where
     }
 }
 
+impl<'a, T: Iterator<Item = bool>> Iterator for BFSKMod<'a, T> {
+    type Item = Complex32;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.step_modulate()
+    }
+}
+
 // FSK Demodulator (dumb non coherent + no symbol timing recovery)
 pub struct BFSKDem {
     samples_per_bit: u32,
diff --git a/src/complex.rs b/src/complex.rs
index 05b892c..622c354 100644
--- a/src/complex.rs
+++ b/src/complex.rs
@@ -2,7 +2,7 @@ use std::{
     f32::consts::PI,
     fmt::Display,
     iter::Sum,
-    ops::{Add, Div, Mul, Neg, Sub},
+    ops::{Add, Deref, Div, Mul, Neg, Sub},
 };
 
 #[derive(Copy, Clone, Debug)]
@@ -130,3 +130,11 @@ impl Sum for Complex32 {
         iter.fold(Complex32::zero(), |acc, el| acc + el)
     }
 }
+
+impl<T> Deref for Complex<T> {
+    type Target = Complex<T>;
+
+    fn deref(&self) -> &Self::Target {
+        self
+    }
+}
diff --git a/src/fft.rs b/src/fft.rs
index 91b068b..e89f185 100644
--- a/src/fft.rs
+++ b/src/fft.rs
@@ -3,7 +3,6 @@ pub mod mixed_radix;
 pub mod rader;
 pub mod rader2;
 pub mod radix2;
-pub mod windows;
 
 use crate::{
     complex::Complex32,
diff --git a/src/filtering.rs b/src/filtering.rs
new file mode 100644
index 0000000..8fce811
--- /dev/null
+++ b/src/filtering.rs
@@ -0,0 +1,2 @@
+mod fir;
+mod impulse_response;
diff --git a/src/filtering/fir.rs b/src/filtering/fir.rs
new file mode 100644
index 0000000..ae083a9
--- /dev/null
+++ b/src/filtering/fir.rs
@@ -0,0 +1,55 @@
+// Finite impulse response filters
+
+use std::collections::VecDeque;
+
+use crate::complex::Complex32;
+
+pub struct FIRFilter<T>
+where
+    T: Iterator<Item = Complex32>,
+{
+    size: usize,
+    impulse_response: Box<[Complex32]>,
+    taps: VecDeque<Complex32>,
+    input: T,
+}
+
+impl<T> FIRFilter<T>
+where
+    T: Iterator<Item = Complex32>,
+{
+    pub fn new(impulse_response: &[Complex32], input: T) -> Self {
+        FIRFilter {
+            size: impulse_response.len(),
+            impulse_response: impulse_response.iter().copied().collect(),
+            taps: VecDeque::from(vec![Complex32::zero(); impulse_response.len()]),
+            input,
+        }
+    }
+}
+
+impl<T> Iterator for FIRFilter<T>
+where
+    T: Iterator<Item = Complex32>,
+{
+    type Item = Complex32;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let _ = self.taps.pop_front();
+
+        let sample = self.input.next();
+        if let None = sample {
+            self.taps.push_back(Complex32::zero());
+            None
+        } else {
+            self.taps.push_back(sample.unwrap());
+            Some(
+                self.taps
+                    .iter()
+                    .zip(self.impulse_response.iter())
+                    .map(|(tap, coef)| *tap * *coef)
+                    .sum(),
+            )
+        }
+    }
+}
diff --git a/src/filtering/impulse_response.rs b/src/filtering/impulse_response.rs
new file mode 100644
index 0000000..8b49119
--- /dev/null
+++ b/src/filtering/impulse_response.rs
@@ -0,0 +1,8 @@
+// Utilities for impulse response design
+
+pub struct WindowIRDesigner {
+    window: fn(f32) -> f32,
+
+    // Ideal requested transfer function
+    transfer_function: Box<[Complex32]>,
+}
diff --git a/src/iq.rs b/src/iq.rs
new file mode 100644
index 0000000..eef7439
--- /dev/null
+++ b/src/iq.rs
@@ -0,0 +1,37 @@
+use crate::{complex::Complex32, nco::Nco};
+
+pub struct IQSampler<T>
+where
+    T: Iterator<Item = f32>,
+{
+    passband: T,
+    local_oscillator: Nco,
+}
+
+impl<T> IQSampler<T>
+where
+    T: Iterator<Item = f32>,
+{
+    fn new(passband: T, center_freq: f32) -> Self {
+        IQSampler {
+            passband,
+            local_oscillator: Nco::new(center_freq),
+        }
+    }
+
+    fn new_from_lo(passband: T, local_oscillator: Nco) -> Self {
+        IQSampler {
+            passband,
+            local_oscillator,
+        }
+    }
+}
+
+impl<T> Iterator for IQSampler<T>
+where
+    T: Iterator<Item = f32>,
+{
+    type Item = Complex32;
+
+    fn next(&mut self) -> Option<Self::Item> {}
+}
diff --git a/src/main.rs b/src/main.rs
index 1059dda..889f5cc 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -10,8 +10,11 @@ use std::{
 mod bfsk;
 mod complex;
 pub mod fft;
+mod filtering;
+mod iq;
 mod nco;
 mod units;
+mod windows;
 
 use bfsk::BFSKMod;
 use complex::Complex;
@@ -59,114 +62,54 @@ fn main() {
 }
 
 fn modulate() {
+    // Modulation parameters
+    let frequency = 2000.;
+    let deviation = 500.;
+
+    // Data parameters
     let sample_rate = 44100;
-    let frequency = 2000.0; //HZ
-    let bandwidth = 400.0; //HZ
-    println!("deviation: {}", PI * (bandwidth / sample_rate as f32));
-
-    let path = "s.txt";
-    let file = File::open(path).unwrap();
-    let mut bit_stream = file.bytes().flat_map(|byte| {
-        let byte = byte.unwrap();
-        [
-            byte & 1 == 1,
-            (byte >> 1) & 1 == 1,
-            (byte >> 2) & 1 == 1,
-            (byte >> 3) & 1 == 1,
-            (byte >> 4) & 1 == 1,
-            (byte >> 5) & 1 == 1,
-            (byte >> 6) & 1 == 1,
-            (byte >> 7) & 1 == 1,
-        ]
-    });
-    //let mut bit_stream = (0..22000).map(|_| false).chain((0..22000).map(|_| true));
-    //let mut bit_stream = (0..22000).flat_map(|_| [true, false]);
-
     let baud_rate = 400;
-    println!("{} samples/bit", sample_rate / baud_rate);
-    let mut bfsk = BFSKMod::new(
+
+    // File to modulate
+    let f = File::open("s.txt").unwrap();
+    let mut bitstream = f.bytes().flat_map(|b| byte_to_bits(b.unwrap()));
+
+    let mut modulator = BFSKMod::new(
         sample_rate / baud_rate,
-        PI * (bandwidth / sample_rate as f32),
-        &mut bit_stream,
+        units::frequency::hz_to_rad_per_sample(deviation, sample_rate as f32),
+        &mut bitstream,
     );
 
+    let mut lo = Nco::new(units::frequency::hz_to_rad_per_sample(
+        frequency,
+        sample_rate as f32,
+    ));
+
     let spec = hound::WavSpec {
         channels: 1,
         sample_rate,
         bits_per_sample: 16,
         sample_format: hound::SampleFormat::Int,
     };
+
     let mut writer = hound::WavWriter::create("sine.wav", spec).unwrap();
-
-    let mut lo = Nco::new(2. * PI * (frequency / sample_rate as f32));
-
-    let prev = Complex::new(0., 0.);
-    let alpha = 1.0 - (-2.0 * PI * ((1.5 * 0.5 * bandwidth) / sample_rate as f32));
-    let mut output_samples = vec![];
-    while let Some(sample) = bfsk.step_modulate() {
+    for (s, up) in modulator.zip(lo) {
+        let sample = (s * up).re; // Project to I coords
         let amplitude = i16::MAX as f32;
-        let c_sample = sample * lo.cexp();
-        //let c_sample = sample;
-
-        //let filtered = prev + (c_sample - prev) * alpha;
-        output_samples.push(c_sample);
-        writer
-            .write_sample((amplitude * c_sample.re) as i16)
-            .unwrap();
-        lo.step();
+        writer.write_sample((sample * amplitude) as i16).unwrap();
     }
     writer.finalize().unwrap();
-
-    let mut of = File::create("out.txt").unwrap();
-
-    let mut fft = FFT::new(110, windows::bartlett);
-    fft.execute(&output_samples);
-
-    let mut csv = File::create("out.csv").unwrap();
-    for x in fft.get_output() {
-        csv.write_all(format!("{},\n", x.mag()).as_bytes()).unwrap();
-    }
-
-    let mut bits = vec![];
-    let mut lodem = Nco::new(-2. * PI * (frequency / sample_rate as f32));
-    let mut demod = BFSKDem::new(
-        sample_rate / baud_rate,
-        PI * (bandwidth / sample_rate as f32),
-    );
-    for chunk in output_samples.chunks((sample_rate / baud_rate) as usize) {
-        let base_chunk: Vec<Complex32> = chunk
-            .iter()
-            .map(|x| {
-                lodem.step();
-                *x * lodem.cexp()
-            })
-            .collect();
-        let bit = demod.demod(base_chunk.as_slice());
-        bits.push(bit);
-        //println!("{:?}", bit)
-    }
-
-    for b in bits.chunks(8) {
-        /*
-        of.write_all(&[(b[7] as u8)
-            | ((b[6] as u8) << 1)
-            | ((b[5] as u8) << 2)
-            | ((b[4] as u8) << 3)
-            | ((b[3] as u8) << 4)
-            | ((b[2] as u8) << 5)
-            | ((b[1] as u8) << 6)
-            | ((b[0] as u8) << 7)])
-            .unwrap();
-        */
-
-        of.write_all(&[(b[0] as u8)
-            | ((b[1] as u8) << 1)
-            | ((b[2] as u8) << 2)
-            | ((b[3] as u8) << 3)
-            | ((b[4] as u8) << 4)
-            | ((b[5] as u8) << 5)
-            | ((b[6] as u8) << 6)
-            | ((b[7] as u8) << 7)])
-            .unwrap();
-    }
+}
+
+fn byte_to_bits(byte: u8) -> Vec<bool> {
+    vec![
+        byte & 1 == 1,
+        (byte >> 1) & 1 == 1,
+        (byte >> 2) & 1 == 1,
+        (byte >> 3) & 1 == 1,
+        (byte >> 4) & 1 == 1,
+        (byte >> 5) & 1 == 1,
+        (byte >> 6) & 1 == 1,
+        (byte >> 7) & 1 == 1,
+    ]
 }
diff --git a/src/units.rs b/src/units.rs
index 352978f..20dc64b 100644
--- a/src/units.rs
+++ b/src/units.rs
@@ -1,17 +1,13 @@
 // Provides nice unit conversions
 
-
-mod frequency
-{
+pub mod frequency {
     use std::f32::consts::PI;
 
-    pub fn hz_to_rad_per_sample(hz: f32, sample_rate: f32) -> f32
-    {
+    pub fn hz_to_rad_per_sample(hz: f32, sample_rate: f32) -> f32 {
         2. * PI * hz / sample_rate
     }
 
-    pub fn rad_per_sample_to_hz(rad: f32, sample_rate: f32) -> f32
-    {
+    pub fn rad_per_sample_to_hz(rad: f32, sample_rate: f32) -> f32 {
         (rad * sample_rate) / (2. * PI)
     }
 }
diff --git a/src/fft/windows.rs b/src/windows.rs
similarity index 71%
rename from src/fft/windows.rs
rename to src/windows.rs
index 9e7882b..c306a16 100644
--- a/src/fft/windows.rs
+++ b/src/windows.rs
@@ -1,4 +1,4 @@
-pub fn rectangular(t: f32) -> f32 {
+pub fn rectangular(_: f32) -> f32 {
     1.
 }