main.lua

-- Wideband FM broadcast radio receiver for luajit & love
-- modified from here https://luaradio.io/examples/rtlsdr-wbfm-stereo.html
-- run with
-- luajit main.lua
-- or
-- love .

local radio = require('radio')

local function playFM(frequency)
    local tune_offset = -250e3
    local source = radio.RtlSdrSource(frequency + tune_offset, 1102500)
    local tuner = radio.TunerBlock(tune_offset, 200e3, 5)
    local fm_demod = radio.FrequencyDiscriminatorBlock(1.25)
    local hilbert = radio.HilbertTransformBlock(129)
    local delay = radio.DelayBlock(129)
    local pilot_filter = radio.ComplexBandpassFilterBlock(129, {18e3, 20e3})
    local pilot_pll = radio.PLLBlock(100, 19e3-50, 19e3+50, 2)
    local mixer = radio.MultiplyConjugateBlock()
    local lpr_filter = radio.LowpassFilterBlock(128, 15e3)
    local lpr_am_demod = radio.ComplexToRealBlock()
    local lmr_filter = radio.LowpassFilterBlock(128, 15e3)
    local lmr_am_demod = radio.ComplexToRealBlock()
    local l_summer = radio.AddBlock()
    local l_af_deemphasis = radio.FMDeemphasisFilterBlock(75e-6)
    local l_downsampler = radio.DownsamplerBlock(5)
    local r_subtractor = radio.SubtractBlock()
    local r_af_deemphasis = radio.FMDeemphasisFilterBlock(75e-6)
    local r_downsampler = radio.DownsamplerBlock(5)
    local top = radio.CompositeBlock()

    local sink

    if love == nil then
        sink = radio.PulseAudioSink(2)
    else
        -- this works, but no audio output...
        sink = radio.RawFileSink('samples.raw')
    end
    
    top:connect(source, tuner, fm_demod, hilbert, delay)
    top:connect(hilbert, pilot_filter, pilot_pll)
    top:connect(delay, 'out', mixer, 'in1')
    top:connect(pilot_pll, 'out', mixer, 'in2')
    top:connect(delay, lpr_filter, lpr_am_demod)
    top:connect(mixer, lmr_filter, lmr_am_demod)
    top:connect(lpr_am_demod, 'out', l_summer, 'in1')
    top:connect(lmr_am_demod, 'out', l_summer, 'in2')
    top:connect(lpr_am_demod, 'out', r_subtractor, 'in1')
    top:connect(lmr_am_demod, 'out', r_subtractor, 'in2')
    top:connect(l_summer, l_af_deemphasis, l_downsampler)
    top:connect(r_subtractor, r_af_deemphasis, r_downsampler)
    
    if love == nil then
        top:connect(l_downsampler, 'out', sink, 'in1')
        top:connect(r_downsampler, 'out', sink, 'in2')
    else
        top:connect(l_downsampler, 'out', sink, 'in')
    end
    return top
end

if love ~= nil then
    function love:draw()
        love.graphics.print("91.5 FM is playing", 10, 10)
    end
end

local myradio = playFM(91.5e6)
myradio:run()