IIR (infinite impulse response)
Based on analog LRC crossover circuits and then modeled in mathematics using discretization or approximations. Quantization comes into play when using a computer. Since it has feedback controlling it, the response to an impulse goes on indefinitely (rounding errors of the approximations). Instead of using decimal numbers it uses fixed numbers (i.e.-1,2,3 instead of 1.234, 1.9845, 3.1467).
Discretization – using mathematical formulas to create models of an analog circuit
Quantization – rounding decimals to whole numbers for example an analog to digital converter. There exists debate about this between 16 bit and 24 bit audio and the ability to distinguish between quiet/soft passages of music and louder counterparts. The overall loudness of newer music has begun to increase due to portable devices, so the varying levels of sound are not as important as older music was once mastered. This is what is considered the “loudness war”. The dynamics of newer recordings are much less than recordings from years ago.
Phase shift of 90 degrees for every 6db/octave
Chebyshev filter, Butterworth filter, Elliptic filter
Fast and Cheap
Easy to implement due to analog counterparts
Poorer bandpass filtering
Rounding errors constantly increase due to feedback or feeding the rounded value back into the system.
• Programs/Software/Hardware using this type
Most car audio crossovers