speaker.lua

local aukit = require("aukit")
local speaker = peripheral.find("speaker")

local file = fs.open("robots.wav", "rb")
local data = file.readAll()
file.close()

-- Create the filters
local function makeBiquad(a0, a1, a2, b0, b1, b2)
    local x1, x2, y1, y2 = 0, 0, 0, 0
    return function(x0)
        local y0 = (b0 / a0) * x0 + (b1 / a0) * x1 + (b2 / a0) * x2 - (a1 / a0) * y1 - (a2 / a0) * y2
        x2, x1 = x1, x0
        y2, y1 = y1, y0
        return y0
    end
end
local function make10(a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, b0, b1, b2, b3, b4 ,b5 ,b6, b7, b8, b9, b10)
    local x1, x2, x3, x4, x5, x6, x7, x8, x9, x10 = 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
    local y1, y2, y3, y4, y5, y6, y7, y8, y9, y10 = 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
    return function (x0)
        local y0 = (b0 / a0) * x0 + (b1 / a0) * x1 + (b2 / a0) * x2 + (b3 / a0) * x3 + (b4 / a0) * x4 + (b5 / a0) * x5 + (b6 / a0) * x6 + (b7 / a0) * x7 + (b8 / a0) * x8 + (b9 / a0) * x9 + (b10 / a0) * x10 - (a1 / a0) * y1 - (a2 / a0) * y2 - (a3 / a0) * y3 - (a4 / a0) * y4 - (a5 / a0) * y5 - (a6 / a0) * y6 - (a7 / a0) * y7 - (a8 / a0) * y8 - (a9 / a0) * y9 - (a10 / a0) * y10
        x10, x9, x8, x7, x6, x5, x4, x3, x2, x1 = x9, x8, x7, x6, x5, x4, x3, x2, x1, x0
        y10, y9, y8, y7, y6, y5, y4, y3, y2, y1 = y9, y8, y7, y6, y5, y4, y3, y2, y1, y0
        return y0
    end
end

-- Parameters; highpass is a 2nd-order butterworth filter, yule is a yulewalk-designed filter based on the equal loudness contours by Robinson and Dadson
local highpass = makeBiquad(
    1,
    -1.9722334,
    0.9726137,
    0.9862118,
    -1.9724236,
    0.9862118
)
local yule = make10(
    1,
    -3.846646,
    7.8150167,
    -11.341703,
    13.055042,
    -12.287599,
    9.482938,
    -5.8725786,
    2.7546587,
    -0.8698438,
    0.13919315,
    0.038575996,
    -0.021603672,
    -0.0012339532,
    -9.291678E-5,
    -0.016552603,
    0.021615269,
    -0.020740451,
    0.0059429808,
    0.0030642801,
    1.2025322E-4,
    0.0028846369
)

-- whether to apply the effect or not
local biquadEnabled = false
for buffer, time in aukit.stream.wav(data, true) do
    local mono = buffer[1]

    if biquadEnabled then
        -- on each sample:
        -- preAmp by approx 10db
        -- apply yule
        -- apply highpass
        -- clamp to [-128, 127]
        for i = 1, #buffer[1] do
            mono[i] = math.max(math.min(127, highpass(yule(mono[i] * 3))), -128)
        end
    end

    -- play the modified buffer
    while not speaker.playAudio(mono) do
        os.pullEvent("speaker_audio_empty")
    end

    -- process inputs if needed
    local event = { os.pullEvent() }
    if event[1] == "key" then
        biquadEnabled = not biquadEnabled
        print("Equal loudness effect enabled: " .. tostring(biquadEnabled))
    end
end