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effects equalizer compressor, limiter noise gates flanger leslie pitch-shift - time scaling time reversal signal restoration Acoustics II: clicks tape speed variations hum noise audio examples back Kurt Heutschi 2013-01-18

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 noise examples I filtering back I attenuation of the low frequency end in PA systems for speech

I of

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 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 of start transients of musical instruments tape speed variations hum I negative slope time constant too small → noise examples : 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 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 → : : 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 (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 phaser leslie pitch-shift - time scaling time reversal I parallel of independent flangers signal restoration clicks I delay times in the order of 10...25 ms tape speed variations hum I listening impression of multiplication of an noise examples instrument or voice back Audio signal processing chorus: example effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal I original sample signal restoration I → original voice clicks tape speed variations hum I Chorus noise examples I → with Chorus back Audio signal processing

effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration phaser clicks tape speed variations hum noise examples back Audio signal processing phaser: principle effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal I summation of the signal and a phase shifted copy signal restoration clicks I slow variation of the phase shift tape speed variations hum I spectral - non-harmonic - amplifications and noise examples attenuations back Audio signal processing

effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration leslie clicks tape speed variations hum noise examples back Audio signal processing leslie: principle effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling I loudspeaker cabinet with rotating chassis time reversal signal restoration I effects: clicks tape speed variations I Doppler effect → frequency shifting hum noise I chassis directivity → amplitude modulation examples I room reflections → varying directional impression back Audio signal processing leslie: example of realization 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 Audio signal processing leslie: sound examples effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal I Hammond organ with Leslie signal restoration clicks I → sequence I + tape speed variations I → sequence II hum noise I → John Lee Hooker: I Cover the Waterfront examples back Audio signal processing

effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration pitch-shift - time scaling clicks tape speed variations hum noise examples back Audio signal processing pitch-shift - time scaling: principle effects equalizer compressor, limiter noise gates I aim: flanger chorus I pitch variation without scaling of the time axis phaser leslie I time axis scaling without pitch variation pitch-shift - time scaling time reversal I principle: signal restoration clicks I audio signal is written in buffer tape speed variations I up-shifting: hum noise I clock of writing data < clock of reading data examples I samples have to synthesized → ”identification of back loops”

I down-shifting:

I clock of writing data > clock of reading data I ”removal of samples” Audio signal processing pitch-shift - time scaling: sound examples effects equalizer compressor, limiter noise gates I original sample flanger chorus I → original phaser leslie I 20 % faster pitch-shift - time scaling time reversal I → 80 % of original length signal restoration clicks tape speed variations I original sample hum noise I → Original examples back I half as fast

I → doubling of length

I twice as fast

I → length halved Audio signal processing

effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration time reversal clicks tape speed variations hum noise examples back Audio signal processing time reversal: audio samples effects equalizer compressor, limiter noise gates flanger chorus phaser leslie I speech: pitch-shift - time scaling time reversal I → original signal restoration clicks I → inverted time axis tape speed variations hum I music: noise examples I → original back I → inverted time axis Audio signal processing

effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal restoration of distorted signal restoration clicks tape speed variations audio signals hum noise examples back Audio signal processing restoration of distorted audio signals effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal I usually applied during transfer of old sound storage signal restoration media to digital formats clicks tape speed variations I vinyl discs → CD hum noise I compact cassettes → CD examples back Audio signal processing restoration of distorted audio signals effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling I typical artifacts of old recordings: time reversal I clicks signal restoration clicks I tape speed fluctuations tape speed variations hum I hum (mains frequency) noise examples I noise back I Audio signal processing restoration of distorted audio signals effects equalizer compressor, limiter noise gates flanger chorus phaser I aims: leslie pitch-shift - time scaling I recovery of the original sound time reversal I in some cases make improvements with respect to signal restoration clicks original sound tape speed variations hum I e.g. extension of a limited frequency response noise examples I in future: model-based solutions back I detection of sound objects I re-synthesis of the signal in perfect audio quality Audio signal processing

effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration removal of clicks clicks tape speed variations hum noise examples back Audio signal processing restoration of distorted audio signals effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling I removal of clicks: time reversal I typical for signals stemming from vinyl discs signal restoration clicks I strategy: tape speed variations hum I detection of the clicks noise I delete and replace the section by estimated signal examples (interpolator) back Audio signal processing

effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal removal of tape speed signal restoration clicks tape speed variations hum variations noise examples back Audio signal processing removal of tape speed variations effects equalizer compressor, limiter noise gates flanger chorus phaser I removal of tape speed variations (→ pitch leslie pitch-shift - time scaling variations): time reversal signal restoration I typical for signals stemming from tape recordings clicks I strategy: tape speed variations hum I short-time spectral analysis with pitch detection noise examples I with a priori knowledge about the original pitch back → identification of the time axis distortion I apply inverse time axis distortion Audio signal processing

effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration removal of hum clicks tape speed variations hum noise examples back Audio signal processing removal of hum effects equalizer compressor, limiter noise gates flanger chorus phaser leslie I removal of hum (and possible harmonics): pitch-shift - time scaling I strategy: time reversal signal restoration I narrow-band notch filter clicks I problem: tape speed variations hum I → notch filter impulse response: pulse at τ = 0 noise examples and at τ = 10ms back I → addition of a sort of echo → possible audible artifacts Audio signal processing

effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration removal of broad-band noise clicks tape speed variations hum noise examples back Audio signal processing removal of broad-band noise effects equalizer compressor, limiter noise gates flanger chorus phaser leslie I removal of broad band noise: pitch-shift - time scaling time reversal I typical for all early sound storage media signal restoration I principle: clicks tape speed variations I establish filter bank with time variable hum noise amplification in each band examples I if signal is present → reference amplification back I dominating noise → very small amplification Audio signal processing removal of broad-band noise effects equalizer compressor, limiter noise gates flanger I strategy: chorus phaser I assumption of constant power spectral density of leslie pitch-shift - time scaling the noise component time reversal I estimation of the noise spectrum in signal pauses signal restoration clicks (”minimum during the whole piece”) tape speed variations hum I short-time spectral analysis of the signal → noise examples evaluation of S/N back I determine amplification of each spectral line from S/N

I delicate choice of the time constant for the amplification adaptation Audio signal processing

effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration examples clicks tape speed variations hum noise examples back Audio signal processing restoration of distorted audio signals: effects example equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration clicks tape speed variations hum De-Noise noise examples back Audio signal processing restoration of distorted audio signals: effects example equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration clicks tape speed variations hum De-Click noise examples back Audio signal processing restoration of distorted audio signals: effects example equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration clicks tape speed variations hum Remove Hum noise examples back Audio signal processing restoration of distorted audio signals: effects example equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration clicks tape speed variations De-Clip hum noise examples back Audio signal processing restoration of distorted audio signals: effects example equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal signal restoration clicks tape speed variations original: original hum noise de-clicking: step 1 examples de-hissing: step 2 back fadings: step 3 Audio signal processing

effects equalizer compressor, limiter noise gates flanger chorus phaser leslie pitch-shift - time scaling time reversal eth-acoustics-2 signal restoration clicks tape speed variations hum noise examples back