Real-time audio programming

time waits for nothing

Daniel Appelt / 2016-11-15

It all started...

...while I was searching for a new MIDI sequencer

Suddenly, I found myself debugging software and reviewing code. I was impressed by how complicated some implementations could get.

Preliminary conclusions

  • I have to write my own Jack MIDI sequencer
  • A Jack MIDI application is just a regular Jack application

Which programming language?

  • Vala
  • Ruby
  • Rust
  • Go
  • D
  • ...

Real-time audio programming 101

time waits for nothing

by Ross Bencina (author of AudioMulch)

Three guiding principles

  • You don't want your audio to glitch
  • Real-time waits for nothing
  • Paranoia is justified

Things to avoid

  • Memory (de)allocation
  • Locking a mutex (see priority inversion)
  • Performing (disk) I/O
  • Calling OS functions that may block
  • Calling code with unpredictable or poor worst-case time complexity
  • Calling code that does or may do any of the above
  • Calling code that you don't trust to be compliant

Things to do

  • Use algorithms with good worst-case time complexity
  • Spread heavy computations across samples / callbacks
  • Pre-allocate or pre-compute data in NRT thread
  • Employ non-shared, audio-callback-only data structures


  • Real-time audio programming is not easy
  • Best-practices for concurrent programming don't apply
  • Avoid GC and other unpredictable run-time libraries
  • Use lock-free FIFO queues to communicate with RT thread

Supercollider as best-practice example

  • Client-server software for live coding and much more
  • Ross Bencina provides valuable insights
  • Its fifo queue implementation is a good starting point to dive into its code

Supercollider communication


  • You better know what you do
  • Maybe it's better to just add a GUI to an existing engine
  • For the brave: Rust should be a nice alternative to C/C++

The end