diff --git a/emulator/core/src/host/mod.rs b/emulator/core/src/host/mod.rs
index 8d274c7..bf77e6f 100644
--- a/emulator/core/src/host/mod.rs
+++ b/emulator/core/src/host/mod.rs
@@ -10,5 +10,5 @@ pub mod audio;
 pub use self::keys::{Key, KeyEvent};
 pub use self::mouse::{MouseButton, MouseEventType, MouseEvent, MouseState};
 pub use self::controllers::{ControllerDevice, ControllerEvent};
-pub use self::traits::{Host, Tty, WindowUpdater, ControllerUpdater, KeyboardUpdater, MouseUpdater, Audio, BlitableSurface, HostData, DummyAudio};
+pub use self::traits::{Host, Tty, WindowUpdater, ControllerUpdater, KeyboardUpdater, MouseUpdater, Audio, BlitableSurface, HostData, ClockedQueue, DummyAudio};
 
diff --git a/emulator/core/src/host/traits.rs b/emulator/core/src/host/traits.rs
index 68fbd48..d0871aa 100644
--- a/emulator/core/src/host/traits.rs
+++ b/emulator/core/src/host/traits.rs
@@ -71,7 +71,7 @@ pub trait MouseUpdater: Send {
 pub trait Audio {
     fn samples_per_second(&self) -> usize;
     fn space_available(&self) -> usize;
-    fn write_samples(&mut self, buffer: &[f32]);
+    fn write_samples(&mut self, clock: Clock, buffer: &[f32]);
     fn flush(&mut self);
 }
 
@@ -118,9 +118,21 @@ impl<T: Clone> ClockedQueue<T> {
         self.0.lock().unwrap().push_back((clock, data));
     }
 
+    pub fn pop_next(&self) -> Option<(Clock, T)> {
+        self.0.lock().unwrap().pop_front()
+    }
+
     pub fn pop_latest(&self) -> Option<(Clock, T)> {
         self.0.lock().unwrap().drain(..).last()
     }
+
+    pub fn unpop(&mut self, clock: Clock, data: T) {
+        self.0.lock().unwrap().push_front((clock, data));
+    }
+
+    pub fn peek_clock(&self) -> Option<Clock> {
+        self.0.lock().unwrap().front().map(|(clock, _)| *clock)
+    }
 }
 
 
@@ -135,7 +147,7 @@ impl Audio for DummyAudio {
         4800
     }
 
-    fn write_samples(&mut self, _buffer: &[f32]) {}
+    fn write_samples(&mut self, _clock: Clock, _buffer: &[f32]) {}
 
     fn flush(&mut self) {}
 }
diff --git a/emulator/frontends/common/src/audio.rs b/emulator/frontends/common/src/audio.rs
index b03d6ae..7c612c6 100644
--- a/emulator/frontends/common/src/audio.rs
+++ b/emulator/frontends/common/src/audio.rs
@@ -1,39 +1,87 @@
 
+use std::sync::{Arc, Mutex};
+use std::collections::VecDeque;
 use cpal::{Sample, Stream, SampleRate, SampleFormat, StreamConfig, traits::{DeviceTrait, HostTrait, StreamTrait}};
 
-use moa_core::host::{HostData, Audio};
+use moa_core::Clock;
+use moa_core::host::{HostData, Audio, ClockedQueue};
 use crate::circularbuf::CircularBuffer;
 
 const SAMPLE_RATE: usize = 48000;
 
 
+#[derive(Clone)]
+pub struct AudioFrame {
+    data: Vec<f32>,
+}
+
 pub struct AudioSource {
+    id: usize,
     sample_rate: usize,
     frame_size: usize,
     sequence_num: usize,
-    mixer: HostData<AudioMixer>,
+    mixer: Arc<Mutex<AudioMixer>>,
     buffer: CircularBuffer<f32>,
+    queue: ClockedQueue<AudioFrame>,
 }
 
 impl AudioSource {
-    pub fn new(mixer: HostData<AudioMixer>) -> Self {
-        let sample_rate = mixer.lock().sample_rate();
-        let frame_size = mixer.lock().frame_size();
+    pub fn new(mixer: Arc<Mutex<AudioMixer>>) -> Self {
+        let queue = ClockedQueue::new();
+        let (id, sample_rate, frame_size) = {
+            let mut mixer = mixer.lock().unwrap();
+            let id = mixer.add_source(queue.clone());
+            (
+                id,
+                mixer.sample_rate(),
+                mixer.frame_size(),
+            )
+        };
         let buffer = CircularBuffer::new(frame_size * 2, 0.0);
 
         Self {
+            id,
             sample_rate,
             frame_size,
             sequence_num: 0,
             mixer,
             buffer,
+            queue,
         }
     }
 
     pub fn space_available(&self) -> usize {
-        self.buffer.free_space() / 2
+        //self.buffer.free_space() / 2
+        self.frame_size / 2
     }
 
+    pub fn fill_with(&mut self, clock: Clock, buffer: &[f32]) {
+        let mut data = vec![];
+        //if self.buffer.free_space() > buffer.len() * 2 {
+            for sample in buffer.iter() {
+                // TODO this is here to keep it quiet for testing, but should be removed later
+                let sample = 0.5 * *sample;
+                data.push(sample);
+                data.push(sample);
+            }
+        //}
+
+        let frame = AudioFrame {
+            data, //: Vec::from(buffer)
+        };
+
+//println!("synthesized {}: {:?}", self.id, frame.data);
+
+        self.queue.push(clock, frame);
+        self.flush();
+    }
+
+    pub fn flush(&mut self) {
+        self.mixer.lock().unwrap().check_next_frame();
+    }
+
+
+    /*
     pub fn fill_with(&mut self, buffer: &[f32]) {
         if self.buffer.free_space() > buffer.len() * 2 {
             for sample in buffer.iter() {
@@ -53,20 +101,31 @@ impl AudioSource {
 
             let mixer_sequence_num = locked_mixer.sequence_num();
             if mixer_sequence_num == self.sequence_num {
+                println!("repeated seq");
                 return;
             }
             self.sequence_num = mixer_sequence_num;
+            println!("flushing to audio mixer {}", self.sequence_num);
 
-            for i in 0..locked_mixer.buffer.len() {
-                locked_mixer.buffer[i] = (locked_mixer.buffer[i] + self.buffer.next().unwrap_or(0.0)).clamp(-1.0, 1.0);
-            }
+            //for i in 0..locked_mixer.buffer.len() {
+            //    locked_mixer.buffer[i] = (locked_mixer.buffer[i] + self.buffer.next().unwrap_or(0.0)).clamp(-1.0, 1.0);
+            //}
+            self.queue.push(0, AudioFrame { data: (0..self.frame_size).map(|_| self.buffer.next().unwrap()).collect() });
 
             self.frame_size = locked_mixer.frame_size();
             self.buffer.resize(self.frame_size * 2);
         }
     }
+    */
 }
 
+// could have the audio source use the circular buffer and then publish to its queue, and then call the mixer to flush if possible,
+// and have the mixer (from the sim thread effectively) build the frame and publish it to its output.  Frames in the source queues
+// could even be 1ms, and the assembler could just fetch multiple frames, adjusting for sim time
+
+
+// you could either only use the circular buffer, or only use the source queue
+
 impl Audio for AudioSource {
     fn samples_per_second(&self) -> usize {
         self.sample_rate
@@ -76,8 +135,8 @@ impl Audio for AudioSource {
         self.space_available()
     }
 
-    fn write_samples(&mut self, buffer: &[f32]) {
-        self.fill_with(buffer);
+    fn write_samples(&mut self, clock: Clock, buffer: &[f32]) {
+        self.fill_with(clock, buffer);
     }
 
     fn flush(&mut self) {
@@ -85,34 +144,58 @@ impl Audio for AudioSource {
     }
 }
 
+use moa_core::host::audio::SquareWave;
+
 #[derive(Clone)]
 pub struct AudioMixer {
     sample_rate: usize,
-    //buffer: CircularBuffer<f32>,
-    buffer: Vec<f32>,
+    frame_size: usize,
     sequence_num: usize,
+    clock: Clock,
+    sources: Vec<ClockedQueue<AudioFrame>>,
+    buffer_underrun: bool,
+    output: Arc<Mutex<AudioOutput>>,
+    test: SquareWave,
 }
 
 impl AudioMixer {
-    pub fn new(sample_rate: usize) -> HostData<AudioMixer> {
-        HostData::new(AudioMixer {
+    pub fn new(sample_rate: usize) -> Arc<Mutex<AudioMixer>> {
+        Arc::new(Mutex::new(AudioMixer {
             sample_rate,
-            //buffer: CircularBuffer::new(1280 * 2, 0.0),
-            buffer: vec![0.0; 1280 * 2],
+            frame_size: 1280,
             sequence_num: 0,
-        })
+            clock: 0,
+            sources: vec![],
+            buffer_underrun: false,
+            output: AudioOutput::new(),
+            test: SquareWave::new(600.0, sample_rate),
+        }))
     }
 
-    pub fn new_default() -> HostData<AudioMixer> {
+    pub fn with_default_rate() -> Arc<Mutex<AudioMixer>> {
         AudioMixer::new(SAMPLE_RATE)
     }
 
+    pub fn add_source(&mut self, source: ClockedQueue<AudioFrame>) -> usize {
+        self.sources.push(source);
+        self.sources.len() - 1
+    }
+
+    pub fn get_sink(&mut self) -> Arc<Mutex<AudioOutput>> {
+        self.output.clone()
+    }
+
     pub fn sample_rate(&self) -> usize {
         self.sample_rate
     }
 
+    pub fn nanos_per_sample(&self) -> Clock {
+        1_000_000_000 as Clock / self.sample_rate as Clock
+    }
+
     pub fn frame_size(&self) -> usize {
-        self.buffer.len()
+        //self.buffer.len()
+        self.frame_size
     }
 
     pub fn sequence_num(&self) -> usize {
@@ -120,17 +203,111 @@ impl AudioMixer {
     }
 
     pub fn resize_frame(&mut self, newlen: usize) {
-        if self.buffer.len() != newlen {
-            self.buffer = vec![0.0; newlen];
+        //if self.buffer.len() != newlen {
+        //    self.buffer = vec![0.0; newlen];
+        //}
+        self.frame_size = newlen;
+    }
+
+    pub fn check_next_frame(&mut self) {
+        if self.output.lock().unwrap().is_empty() {
+            self.assemble_frame();
         }
     }
 
+    pub fn assemble_frame(&mut self) {
+        self.frame_size = self.output.lock().unwrap().frame_size;
+
+        let nanos_per_sample = self.nanos_per_sample();
+        let mut data: Vec<f32> = vec![0.0; self.frame_size];
+
+        if self.buffer_underrun {
+            self.buffer_underrun = false;
+            self.clock += nanos_per_sample * data.len() as Clock;
+            let empty_frame = AudioFrame { data };
+            self.output.lock().unwrap().add_frame(empty_frame.clone());
+            self.output.lock().unwrap().add_frame(empty_frame);
+            return;
+        }
+
+        /*
+        for i in (0..data.len()).step_by(2) {
+            let sample = self.test.next().unwrap() * 0.5;
+            data[i] = sample;
+            data[i + 1] = sample;
+        }
+        */
+
+        let lowest_clock = self.sources
+            .iter()
+            .fold(self.clock, |lowest_clock, source|
+                source
+                    .peek_clock()
+                    .map_or(lowest_clock, |c| c.min(lowest_clock)));
+        self.clock = self.clock.min(lowest_clock);
+
+        for (id, source) in self.sources.iter_mut().enumerate() {
+            let mut i = 0;
+            while i < data.len() {
+                let (clock, frame) = match source.pop_next() {
+                    Some(frame) => frame,
+                    None => {
+                        println!("buffer underrun");
+                        self.buffer_underrun = true;
+                        break;
+                    },
+                };
+
+//println!("clock: {} - {} = {}", clock, self.clock, clock - self.clock);
+                //if clock > self.clock {
+                let start = ((2 * (clock - self.clock) / nanos_per_sample) as usize).min(data.len() - 1);
+                let length = frame.data.len().min(data.len() - start);
+//println!("source: {}, clock: {}, start: {}, end: {}, length: {}", id, clock, start, start + length, length);
+                data[start..start + length].iter_mut().zip(frame.data[..length].iter()).for_each(|(d, s)| *d = (*d + s).clamp(-1.0, 1.0));
+                if length < frame.data.len() {
+                    let adjusted_clock = clock + nanos_per_sample * (length / 2) as Clock;
+                    //println!("unpopping {} {}", clock, adjusted_clock);
+                    source.unpop(adjusted_clock, AudioFrame { data: frame.data[length..].to_vec() });
+                }
+                //}
+                // TODO we need to handle the opposite case
+                i += length;
+            }
+        }
+        self.clock += nanos_per_sample * data.len() as Clock;
+
+//println!("{:?}", data);
+        self.output.lock().unwrap().add_frame(AudioFrame { data });
+    }
+
+/*
     pub fn assembly_frame(&mut self, data: &mut [f32]) {
         self.resize_frame(data.len());
-        for i in 0..data.len() {
-            data[i] = Sample::from(&self.buffer[i]);
-            self.buffer[i] = 0.0;
+        println!("assemble audio frame {}", self.sequence_num);
+
+        //for i in 0..data.len() {
+        //    data[i] = Sample::from(&self.buffer[i]);
+        //    self.buffer[i] = 0.0;
+        //}
+
+        //self.sources
+        //    .iter()
+        //    .filter_map(|queue| queue.pop_latest())
+        //    .fold(data, |data, frame| {
+        //        data.iter_mut()
+        //            .zip(frame.1.data.iter())
+        //            .for_each(|(d, s)| *d = (*d + s).clamp(-1.0, 1.0));
+        //        data
+        //    });
+
+        if let Some((_, last)) = self.output.pop_latest() {
+            self.last_frame = Some(last);
         }
+        if let Some(last) = &self.last_frame {
+            data.copy_from_slice(&last.data);
+        }
+
+        println!("frame {} sent", self.sequence_num);
         self.sequence_num = self.sequence_num.wrapping_add(1); 
 
 /*
@@ -166,7 +343,7 @@ impl AudioMixer {
         }
 */
     }
-
+*/
     // TODO you need a way to add data to the mixer... the question is do you need to keep track of real time
     // If you have a counter that calculates the amount of time until the next sample based on the size of
     // the buffer given to the data_callback, then when submitting data, the audio sources can know that they
@@ -179,12 +356,50 @@ impl AudioMixer {
 
 #[allow(dead_code)]
 pub struct AudioOutput {
-    stream: Stream,
-    mixer: HostData<AudioMixer>,
+    frame_size: usize,
+    sequence_num: usize,
+    last_frame: Option<AudioFrame>,
+    output: VecDeque<AudioFrame>,
 }
 
 impl AudioOutput {
-    pub fn create_audio_output(mixer: HostData<AudioMixer>) -> AudioOutput {
+    pub fn new() -> Arc<Mutex<Self>> {
+        Arc::new(Mutex::new(Self {
+            frame_size: 1280,
+            sequence_num: 0,
+            last_frame: None,
+            output: VecDeque::with_capacity(2),
+        }))
+    }
+
+    pub fn add_frame(&mut self, frame: AudioFrame) {
+        self.output.push_back(frame);
+        self.sequence_num = self.sequence_num.wrapping_add(1);
+        println!("added frame {}", self.sequence_num);
+    }
+
+    pub fn pop_next(&mut self) -> Option<AudioFrame> {
+        println!("frame {} sent", self.sequence_num);
+        self.output.pop_front()
+    }
+
+    pub fn pop_latest(&mut self) -> Option<AudioFrame> {
+        self.output.drain(..).last()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.output.is_empty()
+    }
+}
+
+
+#[allow(dead_code)]
+pub struct CpalAudioOutput {
+    stream: Stream,
+}
+
+impl CpalAudioOutput {
+    pub fn create_audio_output(output: Arc<Mutex<AudioOutput>>) -> CpalAudioOutput {
         let device = cpal::default_host()
             .default_output_device()
             .expect("No sound output device available");
@@ -197,33 +412,21 @@ impl AudioOutput {
             .with_sample_rate(SampleRate(SAMPLE_RATE as u32))
             .into();
 
-        //let channels = config.channels as usize;
+        let data_callback = move |data: &mut [f32], _: &cpal::OutputCallbackInfo| {
+            let result = if let Ok(mut output) = output.lock() {
+                output.frame_size = data.len();
+                output.pop_next()
+            } else {
+                return;
+            };
 
-        let data_callback = {
-            let mixer = mixer.clone();
-            move |data: &mut [f32], _: &cpal::OutputCallbackInfo| {
-                mixer.lock().assembly_frame(data);
-
-/*
-                let mut locked_mixer = mixer.lock();
-                //println!(">>> {} into {}", locked_mixer.buffer.used_space(), data.len());
-
-                // TODO these are quick hacks to delay or shrink the buffer if it's too small or big
-                if locked_mixer.buffer.used_space() < data.len() {
-                    return;
-                }
-                if locked_mixer.buffer.used_space() > data.len() * 2 {
-                    for _ in 0..(locked_mixer.buffer.used_space() - (data.len() * 2)) {
-                        locked_mixer.buffer.next();
-                    }
-                }
-
-                for addr in data.iter_mut() {
-                    let sample = locked_mixer.buffer.next().unwrap_or(0.0);
-                    *addr = Sample::from(&sample);
-                }
-                //locked_mixer.buffer.clear();
-*/
+            if let Some(frame) = result {
+//println!("needs {}, gets {}", data.len(), frame.data.len());
+//println!("{:?}", frame.data);
+                let length = frame.data.len().min(data.len());
+                data[..length].copy_from_slice(&frame.data[..length]);
+            } else {
+                println!("missed a frame");
             }
         };
 
@@ -237,9 +440,8 @@ impl AudioOutput {
 
         stream.play().unwrap();
 
-        AudioOutput {
+        CpalAudioOutput {
             stream,
-            mixer,
         }
     }
 
diff --git a/emulator/frontends/minifb/src/lib.rs b/emulator/frontends/minifb/src/lib.rs
index c3cc781..94d1d9e 100644
--- a/emulator/frontends/minifb/src/lib.rs
+++ b/emulator/frontends/minifb/src/lib.rs
@@ -8,10 +8,10 @@ use minifb::{self, Key, MouseMode, MouseButton};
 use clap::{App, Arg, ArgMatches};
 
 use moa_core::{System, Error, Clock};
-use moa_core::host::{Host, HostData, ControllerUpdater, KeyboardUpdater, KeyEvent, MouseUpdater, MouseState, WindowUpdater, Audio, ControllerDevice};
+use moa_core::host::{Host, ControllerUpdater, KeyboardUpdater, KeyEvent, MouseUpdater, MouseState, WindowUpdater, Audio, ControllerDevice};
 use moa_core::host::gfx::Frame;
 
-use moa_common::audio::{AudioOutput, AudioMixer, AudioSource};
+use moa_common::audio::{AudioOutput, AudioMixer, AudioSource, CpalAudioOutput};
 
 mod keys;
 mod controllers;
@@ -99,7 +99,7 @@ pub struct MiniFrontendBuilder {
     pub controller: Option<Box<dyn ControllerUpdater>>,
     pub keyboard: Option<Box<dyn KeyboardUpdater>>,
     pub mouse: Option<Box<dyn MouseUpdater>>,
-    pub mixer: Option<HostData<AudioMixer>>,
+    pub mixer: Option<Arc<Mutex<AudioMixer>>>,
     pub finalized: bool,
 }
 
@@ -110,7 +110,7 @@ impl MiniFrontendBuilder {
             controller: None,
             keyboard: None,
             mouse: None,
-            mixer: Some(AudioMixer::new_default()),
+            mixer: Some(AudioMixer::with_default_rate()),
             finalized: false,
         }
     }
@@ -180,8 +180,8 @@ pub struct MiniFrontend {
     pub controller: Option<Box<dyn ControllerUpdater>>,
     pub keyboard: Option<Box<dyn KeyboardUpdater>>,
     pub mouse: Option<Box<dyn MouseUpdater>>,
-    pub audio: Option<AudioOutput>,
-    pub mixer: HostData<AudioMixer>,
+    pub audio: Option<CpalAudioOutput>,
+    pub mixer: Arc<Mutex<AudioMixer>>,
 }
 
 impl MiniFrontend {
@@ -190,7 +190,7 @@ impl MiniFrontend {
         controller: Option<Box<dyn ControllerUpdater>>,
         keyboard: Option<Box<dyn KeyboardUpdater>>,
         mouse: Option<Box<dyn MouseUpdater>>,
-        mixer: HostData<AudioMixer>,
+        mixer: Arc<Mutex<AudioMixer>>,
     ) -> Self {
         Self {
             modifiers: 0,
@@ -210,7 +210,7 @@ impl MiniFrontend {
         }
 
         if matches.occurrences_of("disable-audio") <= 0 {
-            self.audio = Some(AudioOutput::create_audio_output(self.mixer.clone()));
+            self.audio = Some(CpalAudioOutput::create_audio_output(self.mixer.lock().unwrap().get_sink()));
         }
 
         let mut options = minifb::WindowOptions::default();
@@ -250,18 +250,19 @@ impl MiniFrontend {
         let mut update_timer = Instant::now();
         let mut last_frame = Frame::new(size.0, size.1);
         while window.is_open() && !window.is_key_down(Key::Escape) {
-            let frame_time = update_timer.elapsed().as_micros();
+            let frame_time = update_timer.elapsed();
             update_timer = Instant::now();
-            println!("new frame after {:?}us", frame_time);
+            println!("new frame after {:?}us", frame_time.as_micros());
 
             let run_timer = Instant::now();
             if let Some(system) = system.as_mut() {
-                system.run_for(nanoseconds_per_frame).unwrap();
+                //system.run_for(nanoseconds_per_frame).unwrap();
+                system.run_for(frame_time.as_nanos() as u64).unwrap();
                 //system.run_until_break().unwrap();
             }
             let sim_time = run_timer.elapsed().as_micros();
             average_time = (average_time + sim_time) / 2;
-            println!("ran simulation for {:?}us in {:?}us (avg: {:?}us)", nanoseconds_per_frame / 1_000, sim_time, average_time);
+            println!("ran simulation for {:?}us in {:?}us (avg: {:?}us)", frame_time.as_nanos() / 1_000, sim_time, average_time);
 
             if let Some(keys) = window.get_keys_pressed(minifb::KeyRepeat::No) {
                 for key in keys {
diff --git a/emulator/peripherals/yamaha/src/sn76489.rs b/emulator/peripherals/yamaha/src/sn76489.rs
index c4b0d99..a0ead1d 100644
--- a/emulator/peripherals/yamaha/src/sn76489.rs
+++ b/emulator/peripherals/yamaha/src/sn76489.rs
@@ -105,7 +105,7 @@ impl Sn76489 {
 }
 
 impl Steppable for Sn76489 {
-    fn step(&mut self, _system: &System) -> Result<ClockElapsed, Error> {
+    fn step(&mut self, system: &System) -> Result<ClockElapsed, Error> {
         let rate = self.source.samples_per_second();
         let available = self.source.space_available();
         let samples = if available < rate / 1000 { available } else { rate / 1000 };
@@ -128,7 +128,7 @@ impl Steppable for Sn76489 {
 
                 buffer[i] = sample.clamp(-1.0, 1.0);
             }
-            self.source.write_samples(&buffer);
+            self.source.write_samples(system.clock, &buffer);
         } else {
             self.source.flush();
         }
diff --git a/emulator/peripherals/yamaha/src/ym2612.rs b/emulator/peripherals/yamaha/src/ym2612.rs
index f75a319..be51e71 100644
--- a/emulator/peripherals/yamaha/src/ym2612.rs
+++ b/emulator/peripherals/yamaha/src/ym2612.rs
@@ -239,7 +239,7 @@ pub fn get_ch_op(bank: usize, reg: usize) -> (usize, usize) {
 
 
 impl Steppable for Ym2612 {
-    fn step(&mut self, _system: &System) -> Result<ClockElapsed, Error> {
+    fn step(&mut self, system: &System) -> Result<ClockElapsed, Error> {
         // TODO since you expect this step function to be called every 1ms of simulated time
         //      you could assume that you should produce (sample_rate / 1000) samples
 
@@ -280,7 +280,8 @@ impl Steppable for Ym2612 {
 
                 buffer[i] = sample.clamp(-1.0, 1.0);
             }
-            self.source.write_samples(&buffer);
+//println!("synthesized: {:?}", buffer);
+            self.source.write_samples(system.clock, &buffer);
         //}
 
         Ok(1_000_000)          // Every 1ms of simulated time