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Diffstat (limited to 'examples/fft.lua')
| -rw-r--r-- | examples/fft.lua | 38 |
1 files changed, 38 insertions, 0 deletions
diff --git a/examples/fft.lua b/examples/fft.lua new file mode 100644 index 0000000..85d0bc2 --- /dev/null +++ b/examples/fft.lua @@ -0,0 +1,38 @@ +-- Plot magnitude of frequency spectrum. +-- Exactly 20 sine cycles in 1024 samples. +-- So this does not need windowing. +tostream(magnitude(FFT(Stream.SinOsc(samplerate*20/1024):sub(1, 1024)))):gnuplot() + +IFFT(FFT(Stream.SinOsc(samplerate*20/1024):sub(1, 1024))):gnuplot() + +-- Here the results are much better with a windowing function. +-- For some strange reason, the window is not necessary to reconstruct the original wave +-- via IFFT(). +tostream(magnitude(FFT(Hamming(Stream.SinOsc(samplerate*20.5/1024):sub(1, 1024))))):gnuplot() + +-- Phase plotting +tostream(phase(FFT(Stream.SinOsc(samplerate*20/1024, 0.7):sub(1, 1024)))):gnuplot() + +-- Naive pitch shifting +-- This is not easy to get right. See https://www.reddit.com/r/DSP/comments/k6t24c/pitch_shifting_algorithm_in_frequency_domain/ +robin = SndfileStream("tracks/robin-mono.wav"):sub(sec(10.284), sec(17.466)):eval() +robin:FFT(1024):map(function(spectrum) + assert(#spectrum == 513) + -- NOTE: We cannot use Stream:resample() as it won't work with complex samples. + for i = 1, 512/2 do spectrum[i] = spectrum[i*2] end + for i = 512/2+1, 512 do spectrum[i] = 0i end + return spectrum +end):IFFT(1024):play() + +-- Noisy stream +noisy = Stream.SinOsc(440):mix(NoiseStream, 0.4) +tostream(magnitude(FFT(Hamming(noisy:sub(1, 1024))))):mul(0.05):gnuplot() + +-- Naive noise canceling +noisy:FFT(1024, Hamming):map(function(spectrum) + assert(#spectrum == 513) + for i = 1, #spectrum do + if (spectrum[i].re^2 + spectrum[i].im^2)^.5*0.05 < 0.8 then spectrum[i] = 0i end + end + return spectrum +end):IFFT(1024):play() |