diff --git a/src/PortAudio.jl b/src/PortAudio.jl
index 3446589..4f5cd01 100644
--- a/src/PortAudio.jl
+++ b/src/PortAudio.jl
@@ -10,19 +10,126 @@ typealias PaStream Void
 const PA_NO_ERROR = 0
 
 # default stream used when none is given
-_stream = Nothing
-_process_tasks = Task[]
+_stream = nothing
 
+################## Types ####################
+
+# A node in the render tree
+abstract AudioNode
+
+# A frame of audio, possibly multi-channel
+typealias AudioBuf Array{Float32}
+
+
+# Info about the hardware device
+type DeviceInfo
+    sample_rate::Integer
+    buf_size::Integer
+end
+
+type AudioStream
+    # TODO: this union may have performance penalties
+    root_node::Union(AudioNode, Nothing)
+    info::DeviceInfo
+
+    function AudioStream(sample_rate, buf_size)
+        new(nothing, DeviceInfo(sample_rate, buf_size))
+    end
+end
+
+function render(node::Nothing, device_input::AudioBuf, info::DeviceInfo)
+    return zeros(info.buf_size)
+end
+
+#### SinOsc ####
+
+# Generates a sin tone at the given frequency
+
+type SinOsc <: AudioNode
+    freq::FloatingPoint
+    phase::FloatingPoint
+
+    function SinOsc(freq::FloatingPoint)
+        new(freq, 0.0)
+    end
+end
+
+function render(node::SinOsc, device_input::AudioBuf, info::DeviceInfo)
+    phase = Float32[1:info.buf_size] * 2pi * node.freq / info.sample_rate
+    phase += node.phase
+    node.phase = phase[end]
+    return sin(phase)
+end
+
+#### AudioMixer ####
+
+# Mixes a set of inputs equally
+
+type AudioMixer <: AudioNode
+    mix_inputs::Array{AudioNode}
+end
+
+function render(node::AudioMixer, device_input::AudioBuf, info::DeviceInfo)
+    # TODO: we may want to pre-allocate this buffer and share between render
+    # calls
+    mix_buffer = zeros(info.buf_size)
+    for in_node in node.mix_inputs
+        mix_buffer += render(in_node, device_input, info)
+    end
+end
+
+#### Array Player ####
+
+# Plays a Vector{Float32} by rendering it out piece-by-piece
+
+type ArrayPlayer <: AudioNode
+    arr::AudioBuf
+    arr_index::Int
+
+    function ArrayPlayer(arr::AudioBuf)
+        new(arr, 1)
+    end
+end
+
+function render(node::ArrayPlayer, device_input::Vector{Float32}, info::DeviceInfo)
+    i = node.arr_index
+    range_end = min(i + info.buf_size, length(node.arr))
+    output = node.arr[i:range_end]
+    if length(output) < info.buf_size
+        output = vcat(output, zeros(info.buf_size - length(output)))
+    end
+    node.arr_index = range_end + 1
+    return output
+end
+
+#### AudioInput ####
+
+# Renders incoming audio input from the hardware
+
+type AudioInput <: AudioNode
+    channel::Int
+end
+
+function render(node::AudioInput, device_input::Vector{Float32}, info::DeviceInfo)
+    @assert size(device_input, 1) == info.buf_size
+    return device_input[:, node.channel]
+end
 
 ############ Exported Functions #############
 
-function play(arr::Array{Float32}, stream)
 
+function register(node::AudioNode, stream::AudioStream)
+    stream.root_node = node
+end
+
+function play(arr::AudioBuf, stream::AudioStream)
+    player = ArrayPlayer(arr)
+    register(player, stream)
 end
 
 function play(arr)
     global _stream
-    if _stream == Nothing
+    if _stream == nothing
         _stream = open_stream()
     end
     play(arr, _stream)
@@ -31,16 +138,22 @@ end
 ############ Internal Functions ############
 
 function open_stream(sample_rate::Int=44100, buf_size::Int=1024)
+    # TODO: handle more streams
     global _stream
-    if _stream != Nothing
+    if _stream != nothing
         error("Currently only 1 stream is supported at a time")
     end
 
+    # TODO: when we support multiple streams we won't set _stream here.
+    # this is just to ensure that only one stream is ever opened
+    _stream = AudioStream(sample_rate, buf_size)
+
+
     fd = ccall((:make_pipe, libportaudio_shim), Cint, ())
 
     info("Launching Audio Task...")
     function task_wrapper()
-        audio_task(fd)
+        audio_task(fd, _stream)
     end
     schedule(Task(task_wrapper))
     # TODO: test not yielding here
@@ -52,18 +165,8 @@ function open_stream(sample_rate::Int=44100, buf_size::Int=1024)
                 sample_rate, buf_size)
     handle_status(err)
     info("Portaudio stream started.")
-end
 
-function process!(out_array, in_array)
-    global phase
-    for i in 1:buf_size
-        out_array[i] = sin(phase)
-        phase += 2pi * freq / sample_rate
-        if phase > 2pi
-            phase -= 2pi
-        end
-    end
-    return buf_size
+    return _stream
 end
 
 function wake_callback_thread(out_array)
@@ -72,15 +175,14 @@ function wake_callback_thread(out_array)
           out_array, size(out_array, 1))
 end
 
-function audio_task(jl_filedesc)
+function audio_task(jl_filedesc::Integer, stream::AudioStream)
     info("Audio Task Launched")
-    in_array = convert(Array{Float32}, zeros(buf_size))
-    out_array = convert(Array{Float32}, zeros(buf_size))
+    in_array = convert(AudioBuf, zeros(stream.info.buf_size))
     desc_bytes = Cchar[0]
     jl_stream = fdio(jl_filedesc)
     jl_rawfd = RawFD(jl_filedesc)
     while true
-        process!(out_array, in_array)
+        out_array = render(stream.root_node, in_array, stream.info)
         # wake the C code so it knows we've given it some more data
         wake_callback_thread(out_array)
         # wait for new data to be available from the sound card (and for it to