The appearance of peaks at incorrect frequencies in a mathematically-processed spectrum due to insufficient density of datapoints in the time-domain spectrum or from peaks outside of the sampled frequency range.This process can be simulated by folding a spectrum that shows the correct wavenumbers back onto itself at ${\tilde{\nu }}_{\mathrm{M}}$ and its multiples.

Range of wavenumber $\tilde{\nu }$	${\tilde{\nu }}_{\mathrm{a}\mathrm{p}\mathrm{p}}$
[${\tilde{\nu }}_{\mathrm{M}}$, 2${\tilde{\nu }}_{\mathrm{M}}$]	2${\tilde{\nu }}_{\mathrm{M}}$ - $\tilde{\nu }$
[2${\tilde{\nu }}_{\mathrm{M}}$, 3${\tilde{\nu }}_{\mathrm{M}}$]	$\tilde{\nu }$ - 2${\tilde{\nu }}_{\mathrm{M}}$
[3${\tilde{\nu }}_{\mathrm{M}}$, 4${\tilde{\nu }}_{\mathrm{M}}$]	4${\tilde{\nu }}_{\mathrm{M}}$ - $\tilde{\nu }$
[4${\tilde{\nu }}_{\mathrm{M}}$, 5${\tilde{\nu }}_{\mathrm{M}}$]	$\tilde{\nu }$ - 4${\tilde{\nu }}_{\mathrm{M}}$