diff --git a/src/bus.rs b/src/bus.rs
index a2420d0..974f1db 100644
--- a/src/bus.rs
+++ b/src/bus.rs
@@ -231,6 +231,10 @@ impl BusIo for Bus {
                     0x1B => self.snd.ch3.len,
                     0x1C => self.snd.ch3.volume(),
                     0x1E => self.snd.ch3.freq_hi.into(),
+                    0x20 => self.snd.ch4.len(),
+                    0x21 => self.snd.ch4.envelope.into(),
+                    0x22 => self.snd.ch4.poly.into(),
+                    0x23 => self.snd.ch4.freq_data.into(),
                     0x24 => self.snd.ctrl.channel.into(),
                     0x25 => self.snd.ctrl.output.into(),
                     0x26 => self.snd.ctrl.status.into(),
@@ -344,6 +348,10 @@ impl BusIo for Bus {
                     0x1C => self.snd.ch3.set_volume(byte),
                     0x1D => self.snd.ch3.freq_lo = byte,
                     0x1E => self.snd.ch3.freq_hi = byte.into(),
+                    0x20 => self.snd.ch4.set_len(byte),
+                    0x21 => self.snd.ch4.envelope = byte.into(),
+                    0x22 => self.snd.ch4.poly = byte.into(),
+                    0x23 => self.snd.ch4.freq_data = byte.into(),
                     0x24 => self.snd.ctrl.channel = byte.into(),
                     0x25 => self.snd.ctrl.output = byte.into(),
                     0x26 => self.snd.ctrl.status = byte.into(), // FIXME: Should we control which bytes are written to here?
diff --git a/src/sound.rs b/src/sound.rs
index 9f4f700..9290f56 100644
--- a/src/sound.rs
+++ b/src/sound.rs
@@ -11,7 +11,8 @@ pub(crate) struct Sound {
     pub(crate) ch2: Channel2,
     /// Wave
     pub(crate) ch3: Channel3,
-    // pub(crate) ch4: Channel4,
+    /// Noise
+    pub(crate) ch4: Channel4,
 }
 
 impl Sound {
@@ -81,6 +82,12 @@ impl From<u8> for FrequencyType {
     }
 }
 
+impl From<FrequencyType> for u8 {
+    fn from(freq_type: FrequencyType) -> Self {
+        freq_type as u8
+    }
+}
+
 impl Default for FrequencyType {
     fn default() -> Self {
         Self::Counter
@@ -377,6 +384,115 @@ impl Default for Channel3Volume {
     }
 }
 
+#[derive(Debug, Clone, Copy, Default)]
+pub(crate) struct Channel4 {
+    /// 0xFF20 | NR41 - Channel 4 Sound Length
+    len: u8,
+    /// 0xFF21 | NR42 - Channel 4 Volume Envelope
+    pub(crate) envelope: VolumeEnvelope,
+    /// 0xFF22 | NR43 - Chanel 4 Polynomial Counter
+    pub(crate) poly: PolynomialCounter,
+    /// 0xFF23 | NR44 - Channel 4 Counter / Consecutive Selector and Restart
+    pub(crate) freq_data: Channel4Frequency,
+}
+
+impl Channel4 {
+    pub(crate) fn len(&self) -> u8 {
+        self.len & 0x3F
+    }
+
+    pub(crate) fn set_len(&mut self, byte: u8) {
+        self.len = byte & 0x3F;
+    }
+}
+
+bitfield! {
+    pub struct PolynomialCounter(u8);
+    impl Debug;
+    freq, set_freq: 7, 4;
+    from into CounterWidth, counter_width, set_counter_width: 3, 3;
+    div_ratio, set_div_ratio: 2, 0;
+}
+
+impl Copy for PolynomialCounter {}
+impl Clone for PolynomialCounter {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl Default for PolynomialCounter {
+    fn default() -> Self {
+        Self(0)
+    }
+}
+
+impl From<u8> for PolynomialCounter {
+    fn from(byte: u8) -> Self {
+        Self(byte)
+    }
+}
+
+impl From<PolynomialCounter> for u8 {
+    fn from(poly: PolynomialCounter) -> Self {
+        poly.0
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub(crate) enum CounterWidth {
+    Long,  // 15 bits long
+    Short, // 7 bits long
+}
+
+impl From<u8> for CounterWidth {
+    fn from(byte: u8) -> Self {
+        match byte & 0x01 {
+            0b00 => Self::Short,
+            0b01 => Self::Long,
+            _ => unreachable!("{:#04X} is not a valid value for CounterWidth"),
+        }
+    }
+}
+
+impl From<CounterWidth> for u8 {
+    fn from(counter_width: CounterWidth) -> Self {
+        counter_width as u8
+    }
+}
+
+bitfield! {
+    pub struct Channel4Frequency(u8);
+    impl Debug;
+    _, set_initial: 7;
+    from into FrequencyType, freq_type, set_freq_type: 6, 6;
+}
+
+impl Copy for Channel4Frequency {}
+impl Clone for Channel4Frequency {
+    fn clone(&self) -> Self {
+        *self
+    }
+}
+
+impl Default for Channel4Frequency {
+    fn default() -> Self {
+        Self(0)
+    }
+}
+
+impl From<u8> for Channel4Frequency {
+    fn from(byte: u8) -> Self {
+        Self(byte & 0xC0) // Only bits 7 and 6 hold anything of value
+    }
+}
+
+impl From<Channel4Frequency> for u8 {
+    fn from(state: Channel4Frequency) -> Self {
+        state.0 & 0x40 // Only bit 6 holds anything of value
+    }
+}
+
 bitfield! {
     pub struct SoundOutput(u8);
     impl Debug;