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I am trying to create short seamless loops of continuous sound.

I recorded myself making an "Aaaaah" sound at 44.1 KHz, and cut this recording to a section containing 4096 samples (giving me slightly under 1/10th of a second of audio).

When I play this in a loop, the sound is very much recognizable but there is of course an audible ticking noise at the point where it is cut.

I applied an FFT transform to this data. When I apply an inverse FFT to the Fourier tables to recreate the signal, the defect is of course still audible.

Is there anything I can do to the Fourier tables to eliminate the defect without changing the other audible properties of the recording? I'm very much uneducated in signal processing, but intuitively I feel that since the ticking sound repeats once per loop, it might be possible to work in the frequency domain to achieve my goal of cleaning it up to produce a seamless continuous sound.

Note: In case there are Javascript programmers here, I created a CodePen here with the "Aaah" loop and its conversion to and from Fourier tables, to facilitate experimentation in code.

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    $\begingroup$ The clicking is due to a time-domain discontinuity in the waveform. You're unlikely to find anything to do in the frequency domain to fix that, short of lowpass-filtering it to the point where the high-frequency content in the click isn't audible. You would likely notice degradation in the sound of interest in that case, though. $\endgroup$
    – Jason R
    Commented Aug 31, 2015 at 19:57
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    $\begingroup$ Thank you! What about a window function? I tried applying a Hanning window to the sample data, and the tick is gone but there is now a vibrating effect since the amplitude increases and decreases during the loop. Could there be a way to process this out? $\endgroup$
    – Clafou
    Commented Aug 31, 2015 at 20:17
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    $\begingroup$ Why not just have a smooth ramp up of a few samples at the beginning of your sample and then a smooth ramp down at the end --- keeping greater than 99% of the samples the same. Using a window across the whole signal will cause a low frequency modulation, which may give the undesirable side tones you are noticing. $\endgroup$
    – Peter K. ♦
    Commented Aug 31, 2015 at 20:46
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    $\begingroup$ Why not use a phase vocoder to do this frame freeze? Its will keep the phase coherence at every 4096 frame. $\endgroup$
    – ederwander
    Commented Aug 31, 2015 at 22:28
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    $\begingroup$ it's the same issue of looping with the samplers from the 80s and 90s. consider AMDF or autocorrelation to find click-free splice points. and then crossfade, in case your splice points are not perfectly matched. $\endgroup$
    – robert bristow-johnson
    Commented Sep 1, 2015 at 0:44

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Try using some sort of pitch estimator to determine the pitch of your sample. Or hum in tune to a note of a known musical pitch (from a pitch pipe for instance). Then overlap and cross-fade frames, not 4k apart, but a shorter distance apart that is an integer multiple of the period corresponding to that pitch.

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