Post on 08-Jan-2016
description
Filters and EQ
Frequency Response Curve
Plots amplitude vs. frequency
Most accurate = Linear/flat amplitude across frequency spectrum
Practical devices ALTER this and in doing so, act as a kind of what? A filter for frequency content!
http://www.headphone.com/buildAGraph.php
Filters and EQ
The most common form of signal processing
Controls amplitude of various frequencies
Controls harmonic or timbral content of a sound
Filter types
4 basic types of filters High pass Low pass Band pass Band reject
Aka notch
High Pass Filter
Pass HighsAttenuate Lows
-cutoff frequency-slope
Stop band Pass band
Low Pass Filter
Pass LowsAttenuate Highs
-cutoff frequency-slope
Stop bandPass band
Band Pass Filter
Center Frequency
Band Pass Filter components
Passes a band of frequencies
2 Cutoff Frequencies
Center Frequency
Quality Factor (Q) Width of bandwidth Narrower = higher Q Q=fc/BW
Fc = center frequency; BW=bandwidth
Band Reject Filter (notch)
Shelving Filters
Discussed briefly in tech 1, but had little use of them with synthesis
Shelving filters are used for attenuation near the extremes of the frequency band High shelf and low shelf; names are inverse of what
the do High shelves remove low frequencies Low shelves remove high frequencies
Shelving filters to not remove frequencies entirely, but instead boost or attenuate after the use of high and low pass filters
Shelving Filters
Equalization
Group of filters sent the same signal in parallel
Each filter is usually a narrow bandpass
Filters are combined to create output sound
Spectrum shaper = each filter has its own output control
Equalization (contd.)
2 types of EQs Graphic EQ
Fixed center frequency, fixed bandwidth, fixed !
Usually features linear faders
Equalization (contd.)
Parametric EQ Fewer filters than graphic Can adjust cf, Q, cut/boost
Importance of EQ
Good equalization is possibly the most important factor in digital audio signal processing
Your processed sounds are only as good as your source recordings
Some things are unavoidable, such as quantization error, but other factors can be limited and removed through EQ
Importance of EQ (contd.)
Low-pass filter – removes high frequency noise, hiss Recordings with high amounts of white noise can
benefit from a high-pass filter. White noise contains random distribution of frequencies across the frequency band; applying a highpass filter removes higher frequency content and softens the added noise to sound more like pink noise
High-pass filter – removes low rumbles, “thud” sounds, woofiness
Importance of EQ
Human ears perceive mid-range frequencies at higher amplitudes than high and low-range frequencies (more on that later)
Recordings that contain high-level mid-range frequencies can sound blurry and unclear Using notch filters to reduce, but not remove, mid-
range frequencies can add clarity to recorded sounds (let’s look at that graphic equalizer on slide 13 again)