RE: Audio synthesis with LuaJIT, and performance
- From: William Adams <william_a_adams@xxxxxxx>
- To: <luajit@xxxxxxxxxxxxx>
- Date: Tue, 5 Jun 2012 02:30:09 +0000
oh yah, and if you use an array allocated like this, don't forget to count from
0 instead of 1. -- William
===============================
- Shaping clay is easier than digging it out of the ground.
http://williamaadams.wordpress.com
http://www.thingiverse.com/WilliamAAdams
https://github.com/Wiladams
From: william_a_adams@xxxxxxx
To: luajit@xxxxxxxxxxxxx
Subject: RE: Audio synthesis with LuaJIT, and performance
Date: Tue, 5 Jun 2012 02:18:12 +0000
I wonder if this little exchange could go more quickly:
local buffer = {} for x = 1, sample_rate * 180 / 1024 do for i = 1, 1024
do buffer[i] = 0 end for i = 1, #voices do
voices[i]:process_buffer(buffer, 1, #buffer) end if play then
for i = 1, #buffer do portaudio.put_sample(buffer[i]/#voices/4)
end end end
First, if you change buffer={} to being an ffi allocated array:
local buffsize = 1024
local buffer = ffi.new("float[?]", buffsize)
Then, in the beginning of the loop, where you're trying to clear it out, you
could do:
ffi.fill(buffer, buffize * ffi.sizeof("float"))
I'm thinking this might be a little bit faster.
-- William
===============================
- Shaping clay is easier than digging it out of the ground.
http://williamaadams.wordpress.com
http://www.thingiverse.com/WilliamAAdams
https://github.com/Wiladams
> From: henk@xxxxxxx
> Date: Mon, 4 Jun 2012 21:47:07 -0400
> Subject: Audio synthesis with LuaJIT, and performance
> To: luajit@xxxxxxxxxxxxx
>
> Hi, I decided it would be a fun experiment to implement a Yamaha
> DX7-style phase modulation synthesizer using LuaJIT. It creates 20
> voices, each with 6 operators running sine waves from a lookup table.
> The source code is pretty straight forward since I haven't yet added
> envelopes or anything else, see synth.lua and synth.c here for lua and
> c implementations:
>
> https://gist.github.com/2871749
>
> I also included portaudio.lua which is a first-pass interface to the
> portaudio push api using the FFI, you can hear the synth by running
> synth.lua with --play.
>
> The performance with the current implementation isn't great, though,
> to generate three minutes of audio took 27.729s for the LuaJIT version
> and 6.996s for the C version, running each three times and taking the
> minimum. The version of LuaJIT used was pulled from git earlier today.
>
> This is after unrolling some loops in the lua version, which made a
> pretty good difference. I also switched to calculating each voice 1024
> samples at a time, rather than iterating through each voice for every
> sample, and this helped as well. Increasing this buffer size more
> helps, but will cause latency problems when I add message-handling to
> the synth. Unfortunately I can't carry that loop down into the
> individual operators since they can have arbitrary mutual recursion,
> and delaying the recursion introduces high-frequency artifacts.
>
> I have plans to runtime-generate lua code per-instrument, since most
> of the modulation matrix is zero for any given instrument, but I'd
> like to take a look at the numerical stuff before I make it more
> complicated.
>
> I don't have much experience optimizing lua code for LuaJIT, but -jv
> seems to suggest everything goes smoothly. Does anyone have advice on
> ways to optimize?
>
> henk
>
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