Aliasfree

Aliasfree is a term used in signal processing to describe systems or techniques that aim to prevent spectral aliasing in their output. Aliasing occurs when a continuous signal is sampled or processed in a way that creates artificial copies of its spectrum within the range of interest, typically due to insufficient sampling rate or imperfect reconstruction. An aliasfree design restricts the signal’s bandwidth, uses appropriate anti-aliasing filters, or employs processing methods that avoid generating frequencies that would alias into the baseband.

In practice, aliasfree implementations rely on several strategies. Before sampling, anti-aliasing filters limit the signal’s bandwidth to at most half the sampling rate. Oversampling can be used to push potential aliased content beyond the output band, followed by careful downsampling with reconstruction filters. In digital audio, aliasfree generation of waveforms is achieved through bandlimited synthesis, which includes methods such as bandlimited waveform generation, minimum BLEP (minBLEP) corrections, and bandlimited impulse trains (BLIT). These techniques aim to produce waveforms (sawtooth, square, etc.) without introducing high-frequency components that would alias when played back at their intended rate. High-quality resampling and reconstruction often employ polyphase filtering or sinc-interpolation to minimize aliasing.

Aliasfree is a design goal rather than an absolute condition, since perfect aliasing elimination is impossible for signals with infinite bandwidth. It is a common consideration in music production, software synthesizers, digital converters, and sample-rate conversion. Related concepts include aliasing, anti-aliasing, oversampling, and the Nyquist rate.