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I am working on algorithms to separate mixtures of 'almost periodic' signals. One such example is composite ECG consisting of maternal and fetal signal.

Can anyone help with examples of such signals? The signal can also be from internet data.

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The sound produced using the lowest pitched strings of large stringed music instruments often includes slightly inharmonic overtones (due to finite string thickness and stiffness), which renders the waveform of the note pitch not quite, but "almost periodic". You can record these sounds from the bottom octaves of most (physical, stringed) pianos, and bass guitars, etc.

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  • $\begingroup$ the other thing that makes musical notes quasi-periodic is that the waveform changes slowly with time. you can think of the Fourier coefficients representing the locally periodic waveform as slowly changing functions rather than as constant. $\endgroup$
    – robert bristow-johnson
    Commented Jan 3, 2014 at 20:17
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Try the so-called MIT DB. They got a few annotated signals.

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