MUST 1220 Lecture Notes - Lecture 18: Low-Pass Filter, High-Pass Filter, Cutoff Frequency

• School: Northeastern University
• Department: Music Technology
• Course: MUST 1220
• Professor: Frengel Mike

Document Summary

Filter = in audio, filtering is spectral shaping. It modifies the spectrum of a signal by emphasizing or deemphasizing certain frequency ranges. White noise = digital / consists of random values only, with no correlation from one sample to the next. The spectrum of a signal created from pure randomness is flat average amplitude of all frequencies is equal. A lowpass filter reduces or eliminates higher fre(cid:395)ue(cid:374)(cid:272)ies (cid:894)lets the (cid:862)lo(cid:449)s pass(cid:863)(cid:895). Amplitude on output is 0. 707 of its amplitude on input. Cutoff frequency represents the half-power level = -3 db. Audio signals must be lowpass filtered before its sampled to eliminate frequencies above the nyquist frequency (aliasing) Feedforward filter = creates dips (cid:894)(cid:862)ze(cid:396)oes(cid:863)(cid:895) i(cid:374) the spe(cid:272)t(cid:396)u(cid:373) of its i(cid:374)put. Feedback filter = (cid:894)aka (cid:396)eso(cid:374)a(cid:374)t filte(cid:396) o(cid:396) (cid:396)e(cid:272)u(cid:396)si(cid:448)e filte(cid:396)(cid:895) adds a spe(cid:272)t(cid:396)al (cid:862)hu(cid:373)p(cid:863) (cid:374)ea(cid:396) the (cid:272)utoff frequency. Filter resonates at this spectral peak and adds a distinct coloration to the input that is often used in musical applications.