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Filters and EQ

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.

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Filters and EQ

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  1. Filters and EQ

  2. 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

  3. Filters and EQ • The most common form of signal processing • Controls amplitude of various frequencies • Controls harmonic or timbral content of a sound

  4. Filter types • 4 basic types of filters • High pass • Low pass • Band pass • Band reject • Aka notch

  5. High Pass Filter Slope Stop band Pass band • Pass Highs • Attenuate Lows • cutoff frequency • slope

  6. Low Pass Filter Pass band Stop band Slope • Pass Lows • Attenuate Highs • cutoff frequency • slope

  7. Band Pass Filter Center Frequency

  8. 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

  9. Band Reject Filter (notch)

  10. 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

  11. Shelving Filters

  12. 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

  13. Equalization (contd.) • 2 types of EQs • Graphic EQ • Fixed center frequency, fixed bandwidth, fixed ! • Usually features linear faders

  14. Equalization (contd.) • Parametric EQ • Fewer filters than graphic • Can adjust cf, Q, cut/boost

  15. 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

  16. 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

  17. 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)

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