Anti-Aliasing Filter

Anti-aliasing filters are low-pass filters that attenuate frequencies near the Nyquist frequency (half the sampling rate) to prevent aliasing artifacts during digital conversion. A steeper (“sharp”) filter maintains a linear frequency response up to the cutoff frequency but introduces increased ringing artifacts in the impulse response due to its abrupt transition. In contrast, a “slow” filter with a gentler slope may cause slight attenuation of high frequencies (treble), which can be audible at standard sampling rates, but provides a near-perfect impulse response with minimal ringing.

By default, the M-32 AD Pro II-D employs a sharp filter with short delay at standard sampling rates (44.1 kHz and 48 kHz) and a slow filter with short delay at higher sampling rates (88.2 kHz, 96 kHz, and above). However, the filter settings can be adjusted globally This flexibility is beneficial when maintaining a linear frequency response in the ultrasonic range is important for the given application (ie. measurements).

The Short-Delay options are IIR filters that reduce the overall delay of the conversion to a few samples, while the other two filters are FIR filters offer phase-linearity across the entire frequency range.