Goertzel frequency analyzer

goertzel_freq.lua

-- Frequency analyzer
local function goertzel(samples, sample_rate, freq)
	-- Get coefficient from target and maximal frequency
	local coeff = 2 * math.cos(2 * math.pi * freq / sample_rate)
	-- Process samples
	local s_prev, s_prev2, s = 0, 0
	for i=1, #samples do
		s = samples[i] + coeff * s_prev - s_prev2
		s_prev2, s_prev = s_prev, s
	end
	-- Calculate power of target frequency
	return s_prev2 * s_prev2 + s_prev * s_prev - coeff * s_prev * s_prev2
end

-- Audio data (sample_type: double; channels: 1)
local sample_rate, seconds, frequency = 22050, 3, 400
local samples = {}
for i=1, seconds * sample_rate do
	samples[i] = math.sin(2 * math.pi * (i-1) / sample_rate * frequency)
end

-- Test
print(
	"Power: " .. goertzel(samples, sample_rate, 400)
)