groovy_client.lua

local function split (inputstr, sep)
    if sep == nil then
            sep = "%s"
    end
    local t={}
    for str in string.gmatch(inputstr, "([^"..sep.."]+)") do
            table.insert(t, str)
    end
    return t
end

local modemSide, speakerSide = ...

local listenId = nil

rednet.open(modemSide)
local speaker = peripheral.wrap(speakerSide)

while true do
    senderId, message, distance, protocol = rednet.receive()

    params = split(message, ",")
    cmd = params[1]

    if listenId == senderId and cmd == "groovy_play" then
        speaker.playNote(params[2], tonumber(params[3]), tonumber(params[4]))
    end

    if cmd == "groovy_start" then
        listenId = senderId
    elseif cmd == "groovy_stop" then
        listenId = nil
    end
end