Miscellaneous Lisp Hackery

Here's a few things I've been working on lately which may be of broader interest:

Bordeaux-FFT is a small library for computing the FFT/IFFT on complex data, originally written by Robert Strandh (and/or Sylvain Marchand and Martin Raspaud), with contributions by Paul Khuong and myself. Last summer I did some audio processing experiments, originally using the FFT code from Sapaclisp. Robert helpfully volunteered his FFT implementation, which I cleaned up slightly and have been cheerfully employing in various audio hacks ever since. Several versions have changed hands through email, lisppaste, and my web server, so I've finally come around to collecting the changes, writing a brief manual, and tarring up a release. It's surprisingly fast, particularly with Paul Khuong's recent work on SBCL, although I don't know how it stacks up against some of the highly tuned assembly language implementations out there. I use it along with my fledgling task queuing code to grind out batches of FFTs across four CPU cores.

Shuffletron is a simple music player in CL, with a few interesting features. I've been running this program full time for several weeks now as my preferred music player. It snuck on to the lisp subreddit before I really announced it, and I'm sure folks on IRC are already sick of hearing about it, so I won't say much. I began with plans for a much more ambitious player, with a fancy graphical interface, and wrote the first version of this one Saturday realizing I needed something simple to put the audio code through its paces while I wrote the full player, intending to include this one as an example program with Mixalot. It worked better than expected, so I ended up fleshing out the feature set instead and decided that it was really all I needed. The code is lean and mean.

I've had a number of problems trying to produce redistributable binaries of this which I believe I've finally solved (although new binaries are forthcoming). I hope to write about these later.

Mixalot is the audio back-end of Shuffletron, factored into its own system(s) because it might be useful for other purposes. It includes a mixer which pulls audio from any number of streamer objects and outputs them to ALSA. It also includes FFI definitions for libmpg123 with some helpers for decoding MP3 files and reading ID3 tags, and a streamer class for decoding and playing MP3 files in real time. The libmpg123 portions are usable independently of the audio mixing/output code.