[sdiy] Raspberry Pi 2 Synthesizer Project

[Scott Gravenhorst]

If you're on music-dsp, you already know about this.

I purchased a Raspberry Pi 2 a bit before Christmas and have been 
working on a synthesizer.  Quad core ARMv7 900 MHz CPU.  I also have the 
Cirrus Logic/Element14 sound card (24 bit stereo up to 192 kHz. 
Line-in, line-out, S/PDIF and other features).

So far, using ALSA, I've made an organ type polysynth (32 voices).  Each 
voice is computed arithmetically as y=sin(a)+sin(2a).  I've isolated 2 
of the 4 cores so that the synth runs in one core and the MIDI 
controller runs in another though the MIDI controller seems to run fine 
along side other linux stuff in a shared core.  It's currently working 
while LXDE deskstop runs.  The synth core uses about 55% CPU at idle and 
around 80% when using most of the voices.  No crashes or glitches.  I 
will need to measure latency, but the latency contributed by ALSA 
buffering is down around 1/6 millisecond (period is 8 frames and the 
sample rate is 44100 Hz).

I'm quite impressed by the power of this little thing, especially for a 
$35 computer board.

-- ScottG