In signal processing, apodization (from Greek "removing the foot") is the modification of the shape of a mathematical function. The function may represent an electrical signal, an optical transmission or a mechanical structure. In optics, it is primarily used to remove Airy disks caused by diffraction around an intensity peak, improving the focus. Apodization in electronics Apodization in signal processing The term apodization is used frequently in publications on Fourier-transform infrared (FTIR) signal processing. An example of apodization is the use of the Hann window in the fast Fourier transform analyzer to smooth the discontinuities at the beginning and end of the sampled time record. Apodization in digital audio An apodizing filter can be used in digital audio processing instead of the more common brick-wall filters, in order to avoid the pre-ringing that the latter introduces. Apodization in mass spectrometry During oscillation within an Orbitrap, ion transient signal may not be stable until the ions settle into their oscillations. Toward the end, subtle ion collisions have added up to cause noticeable dephasing. This presents a problem for the Fourier transformation, as it averages the oscillatory signal across the length of the time-domain measurement. The software allows “apodization”, the removal of the front and back section of the transient signal from consideration in the FT calculation. Thus, apodization improves the resolution of the resulting mass spectrum. Another way to improve the quality of the transient is to wait to collect data until ions have settled into stable oscillatory motion within the trap. Apodization in nuclear magnetic resonance spectroscopy Apodization is applied to NMR signals before discrete Fourier Transformation. Typically, NMR signals are truncated due to time constraints (indirect dimension) or to obtain a higher signal-to-noise ratio. In order to reduce truncation artefacts, the signals are subjected to apodization with different types of window functions. Apodization in optics In optical design jargon, an apodization function is used to purposely change the input intensity profile of an optical system, and may be a complicated function to tailor the system to certain properties. Usually it refers to a non-uniform illumination or transmission profile that approaches zero at the edges. Apodization in imaging Since side lobes of the Airy disk are responsible for degrading the image, techniques for suppressing them are utilized. In case the imaging beam has Gaussian distribution, when the truncation ratio (the ratio of the diameter of the Gaussian beam to the