[sdiy] Raspberry Pi 2 Synthesizer Project

[Scott Gravenhorst]

Richie Burnett <rburnett at richieburnett.co.uk> wrote:
 >Sounds good. What did you write the code in? Assembly, C, python?

The code is written entirely in C.  It's pretty much raw unoptimized 
code, so performance could increase with more attention to that.  Once I 
learn ARM assembly language (a bit more complex than PIC/dsPIC) I may 
include some of that for tightness.  The synth currently has no GUI, so 
it can run headless if needed.  I'm thinking about adding another 
different synth to make it bi-timbral, and eventually I'll add effects.

-- ScottG

 >---- Scott Gravenhorst wrote ----
 >
 >>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