Audio signal processing effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration Acoustics II: clicks tape speed variations hum noise audio signal processing examples back Kurt Heutschi 2013-01-18 Audio signal processing effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration effects clicks tape speed variations hum noise examples back Audio signal processing effects: introduction effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling I effects: alteration of the original sound such as: time reversal I adjustment of the frequency response signal restoration clicks I reduction of the audibility of unwanted signal tape speed variations hum components noise examples I .... back I creation of new sounds Audio signal processing effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration equalizer clicks tape speed variations hum noise examples back Audio signal processing equalizer: function effects equalizer compressor, limiter noise gates flanger I function: chorus phaser I manipulation of the amplitude response of a sound leslie pitch-shift - time scaling or a transmission system time reversal I applications: signal restoration clicks I flatten a non-ideal frequency response of a tape speed variations hum loudspeaker noise examples I loudness filtering back I attenuation of the low frequency end in PA systems for speech I equalization of headphones I .... Audio signal processing equalizer: realizations effects equalizer compressor, limiter noise gates flanger chorus phaser leslie I parametric equalizer: pitch-shift - time scaling time reversal I several bandpass/notch filters with variable signal restoration I center frequency clicks tape speed variations I bandwidth hum I amplification/attenuation noise examples I universal applicability, however not that intuitive back to reproduce a predefined amplitude response Audio signal processing equalizer: realizations effects I graphical equalizer: equalizer compressor, limiter I series of adjacent bandpass filters of constant noise gates flanger relative bandwidth chorus phaser I third-octave filters (typ. 30 bands) leslie I octave filters (typ. 10 bands) pitch-shift - time scaling time reversal I adjustable amplification/attenuation in each band signal restoration (typ. +/- 15 dB) clicks tape speed variations I setting with linear controllers ! graphical hum noise representation of the amplitude response examples back Audio signal processing effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration compressor/limiter clicks tape speed variations hum noise examples back Audio signal processing compressor/limiter: function effects equalizer compressor, limiter noise gates flanger I function: chorus phaser I reduction of the signal dynamics leslie pitch-shift - time scaling I applications for compressors: time reversal I increase of loudness with given maximal signal signal restoration clicks amplitude tape speed variations hum I music production noise I commercials examples back I radio stations (listeners are often in noisy environment) I applications for limiters: I avoid clipping in digital recordings Audio signal processing compressor/limiter: principle of operation effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration clicks tape speed variations hum noise examples back I VCA: Voltage Controlled Amplifier I steering voltage: smoothed input signal I amplification is lowered above an adjustable threshold Audio signal processing compressor/limiter: characteristics effects equalizer I example (threshold = 0 dB) compressor, limiter noise gates I input level ! amplification flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration clicks tape speed variations hum noise examples back Audio signal processing compressor/limiter: characteristics effects equalizer I example (threshold = 0 dB) compressor, limiter noise gates I input level ! output level flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration clicks tape speed variations hum noise examples back Audio signal processing compressor/limiter: time constants effects I VCA is steered by the level of the audio signal equalizer compressor, limiter I determination of the level needs an average process noise gates flanger I choice of the time constant is critical chorus phaser I implementation of two constants: positive for signal leslie pitch-shift - time scaling increase and negative for signal decrease time reversal signal restoration I positive slope time constant too small ! clicks distortion of start transients of musical instruments tape speed variations hum I negative slope time constant too small ! noise examples pumping: modulation of the signal by dominant back components I positive/negative slope time constant too large ! signal dynamics is not properly reduced due to delayed reaction I typical values: I positive slope: order of milliseconds I negative slope: 10 to 3000 milliseconds Audio signal processing compressor/limiter: example effects equalizer compressor, limiter noise gates flanger chorus phaser leslie I original sample pitch-shift - time scaling time reversal I ! original signal restoration clicks I compression starting 25 dB below full-scale ! tape speed variations hum approx. 10 dB higher signal power at identical peak noise examples value back I ! with compression Audio signal processing compressor/limiter: finalizer effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling I loudness war time reversal I producers push perceived loudness to maximum signal restoration clicks I increasing concern regarding audio quality tape speed variations hum I loss in dynamic range noise I unofficial dynamic range data base: examples back http://www.dr.loudness-war.info/ Audio signal processing compressor/limiter: finalizer: loudness war effects equalizer compressor, limiter noise gates flanger chorus phaser ! Metallica: Death Magnetic: My Acopalypse, 2008 leslie pitch-shift - time scaling time reversal signal restoration clicks tape speed variations hum noise examples back Audio signal processing effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration noise gates clicks tape speed variations hum noise examples back Audio signal processing noise gates: function effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal I function: signal restoration I attenuation of low level signals clicks tape speed variations I applications: hum noise examples I suppression of noise during pauses of the signal back Audio signal processing noise gates effects equalizer compressor, limiter I parameters: level and step noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration clicks tape speed variations hum noise examples back Audio signal processing effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration flanger clicks tape speed variations hum noise examples back Audio signal processing flanger: principle effects equalizer compressor, limiter noise gates flanger I summation of signal and a delayed copy chorus phaser leslie I slow variation (0.1 Hz) of the delay (couple of pitch-shift - time scaling time reversal milliseconds) signal restoration clicks tape speed variations hum noise examples back Audio signal processing flanger: comb filter effects equalizer I ! comb filter for delay τ: compressor, limiter noise gates 1 2 3 I maxima: f = 0; ; ; flanger τ τ τ chorus phaser 1 3 5 I minima: f = ; ; leslie 2τ 2τ 2τ pitch-shift - time scaling time reversal signal restoration clicks tape speed variations hum noise examples back Audio signal processing flanger: comb filter effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal I time dependency of the delay variation function signal restoration I e.g. sinusoidal ! uneven variation of the clicks tape speed variations maxima/minima frequencies hum noise I in general ! non-sinusoidal time function examples back Audio signal processing flanger: comb filter effects equalizer compressor, limiter noise gates flanger chorus I example of a non-sinusoidal time function of the phaser delay: leslie pitch-shift - time scaling time reversal signal restoration clicks tape speed variations hum noise examples back Audio signal processing flanger: example effects I original sample equalizer compressor, limiter I ! original noise gates flanger I Flanger minDelay: 0.5ms, maxDelay: 5ms, variation: chorus phaser sinusoidal with 0.1Hz leslie pitch-shift - time scaling I ! with Flanger time reversal signal restoration spectrogram: clicks tape speed variations hum noise examples back Audio signal processing effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration chorus clicks tape speed variations hum noise examples back Audio signal processing chorus: principle effects equalizer compressor, limiter noise gates flanger chorus