TFCS

Toolbox for the Feedback Control of Sound

Edgar Berdahl


What is TFCS?

A toolbox demonstrating how to integrate RTAI, Comedi, STK, and OSC for controlling vibration and sound.

Feedback control of sound requires low-latency signal processing. In addition, because the human range of hearing extends roughly from 20Hz to 20kHz, controller hardware must process signals with relatively large bandwidths in comparison with common control applications. Over the past decade, the appropriate embedded hardware has become a niche product, so its cost has actually increased. The open source community has developed an excellent alternative: a general-purpose computer runs Linux with the Real- Time Application Interface (RTAI). Open source drivers (see www.comedi.org) enable software to communicate efficiently with data acquisition cards. For the first time, we describe in detail from start to finish how to configure such a system. In particular, we explain how to run control code from user space while still disabling interrupts. We further explain how to reserve a processor for running only feedback control code. This configuration achieves less than one sample of total system delay at sampling rates as high as 50kHz. Other processors remain free to run standard Linux programs, allowing researchers to control sound with calls to many generic software libraries. We present detailed measurements of system jitter for various configurations and provide an example open- source toolbox demonstrating all these aspects on this web site.

MORE INFORMATION HERE

E. Berdahl, N. Lee, G. Niemeyer, J. O. Smith III
Practical implementation of low-latency DSP for feedback control of sound in research contexts,
Second joint conference of the Acoustical Society of America (ASA)
and the European Acoustics Association (EAA), also known as Acoustics '08,
June 29-July 4, 2008 - Paris, France.



Why this toolbox?
  1. Now that general-purpose computers usually have multiprocessors, this method for implementing control hardware supporting large enough bandwidths for controlling sound is convenient and inexpensive.
  2. The information is now all available in one place.
  3. We believe that low-latency high bandwidth control should be available to everyone.
  4. During the course of implementing our own system, we too often came across messages on newsgroups like "Well, it isn't straight-forward, but we had to write our own code because we couldn't find appropriate starter code anywhere. You will figure it out eventually!"



Release (4/24/08):


What we are doing with it:



To Edgar Berdahl's Web Page

To Julius O. Smith III's Web Page