[LAD] Smallest, simplest, silliest SDR?

Gordon JC Pearce gordonjcp at gjcp.net
Sun Feb 28 00:40:00 UTC 2010

I wanted a very simple SDR with jack inputs and outputs for a
demonstration I was doing.  I had a look at the DSP guts of dttsp and
quisk, and sat down to code.

Now, since I wanted to demonstrate how you could use LADSPA filters to
clean up received audio, it occurred to me that I should implement my
SDR core as a LADSPA plugin.  So, I did.

It "works for me".  If you try it out, let me know how you get on.  At
256 frames/period it sits at about 3% usage on my P4-2.8 without any
other LADSPAs running - not bad, but it probably could be better.

If you want to build it, get the code with:

git clone git://lovesthepython.org/ladspa-sdr.git

then build it with scons.  You'll need to manually copy the resulting
sdr.so to wherever your LADSPA plugins live.  Load it up in jack-rack
and add in an amplifier plugin (there's no AGC) and some sort of filter
(I recommend the Glame Bandpass Filter).

Performance and quality isn't exactly amazing, but for less than 300
lines of code - much of that used to set up the plugin - it's not too

Gordon MM0YEQ

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