audio signal processing - eth zisistaff/courses/ak2/... · audio signal processing e ects equalizer...
TRANSCRIPT
Audio signalprocessing
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
Acoustics II:audio signal processing
Kurt Heutschi2013-01-18
Audio signalprocessing
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
effects
Audio signalprocessing
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
effects: introduction
I effects: alteration of the original sound such as:I adjustment of the frequency responseI reduction of the audibility of unwanted signal
componentsI ....I creation of new sounds
Audio signalprocessing
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
equalizer
Audio signalprocessing
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
equalizer: function
I function:I manipulation of the amplitude response of a sound
or a transmission system
I applications:I flatten a non-ideal frequency response of a
loudspeakerI loudness filteringI attenuation of the low frequency end in PA
systems for speechI equalization of headphonesI ....
Audio signalprocessing
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
equalizer: realizations
I parametric equalizer:I several bandpass/notch filters with variable
I center frequencyI bandwidthI amplification/attenuation
I universal applicability, however not that intuitiveto reproduce a predefined amplitude response
Audio signalprocessing
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
equalizer: realizations
I graphical equalizer:I series of adjacent bandpass filters of constant
relative bandwidthI third-octave filters (typ. 30 bands)I octave filters (typ. 10 bands)
I adjustable amplification/attenuation in each band(typ. +/- 15 dB)
I setting with linear controllers → graphicalrepresentation of the amplitude response
Audio signalprocessing
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
compressor/limiter
Audio signalprocessing
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
compressor/limiter: function
I function:I reduction of the signal dynamics
I applications for compressors:I increase of loudness with given maximal signal
amplitudeI music productionI commercialsI radio stations (listeners are often in noisy
environment)
I applications for limiters:I avoid clipping in digital recordings
Audio signalprocessing
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
compressor/limiter: principle of operation
I VCA: Voltage Controlled Amplifier
I steering voltage: smoothed input signal
I amplification is lowered above an adjustablethreshold
Audio signalprocessing
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
compressor/limiter: characteristics
I example (threshold = 0 dB)
I input level → amplification
Audio signalprocessing
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
compressor/limiter: characteristics
I example (threshold = 0 dB)
I input level → output level
Audio signalprocessing
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
compressor/limiter: time constantsI VCA is steered by the level of the audio signal
I determination of the level needs an average process
I choice of the time constant is criticalI implementation of two constants: positive for signal
increase and negative for signal decreaseI positive slope time constant too small →
distortion of start transients of musical instrumentsI negative slope time constant too small →
pumping: modulation of the signal by dominantcomponents
I positive/negative slope time constant too large →signal dynamics is not properly reduced due todelayed reaction
I typical values:I positive slope: order of millisecondsI negative slope: 10 to 3000 milliseconds
Audio signalprocessing
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
compressor/limiter: example
I original sampleI → original
I compression starting 25 dB below full-scale →approx. 10 dB higher signal power at identical peakvalue
I → with compression
Audio signalprocessing
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
compressor/limiter: finalizer
I loudness warI producers push perceived loudness to maximumI increasing concern regarding audio qualityI loss in dynamic rangeI unofficial dynamic range data base:
http://www.dr.loudness-war.info/
Audio signalprocessing
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
compressor/limiter: finalizer: loudness war
→ Metallica: Death Magnetic: My Acopalypse, 2008
Audio signalprocessing
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
noise gates
Audio signalprocessing
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
noise gates: function
I function:I attenuation of low level signals
I applications:I suppression of noise during pauses of the signal
Audio signalprocessing
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
noise gates
I parameters: level and step
Audio signalprocessing
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
flanger
Audio signalprocessing
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
flanger: principle
I summation of signal and a delayed copy
I slow variation (0.1 Hz) of the delay (couple ofmilliseconds)
Audio signalprocessing
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
flanger: comb filter
I → comb filter for delay τ :I maxima: f = 0, 1
τ ,2τ ,
3τ
I minima: f = 12τ ,
32τ ,
52τ
Audio signalprocessing
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
flanger: comb filter
I time dependency of the delay variation functionI e.g. sinusoidal → uneven variation of the
maxima/minima frequenciesI in general → non-sinusoidal time function
Audio signalprocessing
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
flanger: comb filter
I example of a non-sinusoidal time function of thedelay:
Audio signalprocessing
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
flanger: exampleI original sample
I → original
I Flanger minDelay: 0.5ms, maxDelay: 5ms, variation:sinusoidal with 0.1Hz
I → with Flanger
spectrogram:
Audio signalprocessing
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
chorus
Audio signalprocessing
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
chorus: principle
I parallel arrangement of independent flangers
I delay times in the order of 10. . .25 ms
I listening impression of multiplication of aninstrument or voice
Audio signalprocessing
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
chorus: example
I original sampleI → original voice
I ChorusI → with Chorus
Audio signalprocessing
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
phaser
Audio signalprocessing
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
phaser: principle
I summation of the signal and a phase shifted copy
I slow variation of the phase shift
I spectral - non-harmonic - amplifications andattenuations
Audio signalprocessing
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
leslie
Audio signalprocessing
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
leslie: principle
I loudspeaker cabinet with rotating chassis
I effects:I Doppler effect → frequency shiftingI chassis directivity → amplitude modulationI room reflections → varying directional impression
Audio signalprocessing
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
leslie: example of realization
Audio signalprocessing
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
leslie: sound examples
I Hammond organ with LeslieI → sequence I +I → sequence III → John Lee Hooker: I Cover the Waterfront
Audio signalprocessing
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
pitch-shift - time scaling
Audio signalprocessing
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
pitch-shift - time scaling: principle
I aim:I pitch variation without scaling of the time axisI time axis scaling without pitch variation
I principle:I audio signal is written in bufferI up-shifting:
I clock of writing data < clock of reading dataI samples have to synthesized → ”identification of
loops”I down-shifting:
I clock of writing data > clock of reading dataI ”removal of samples”
Audio signalprocessing
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
pitch-shift - time scaling: sound examples
I original sampleI → original
I 20 % fasterI → 80 % of original length
I original sampleI → Original
I half as fastI → doubling of length
I twice as fastI → length halved
Audio signalprocessing
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
time reversal
Audio signalprocessing
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
time reversal: audio samples
I speech:I → originalI → inverted time axis
I music:I → originalI → inverted time axis
Audio signalprocessing
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
restoration of distortedaudio signals
Audio signalprocessing
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
restoration of distorted audio signals
I usually applied during transfer of old sound storagemedia to digital formats
I vinyl discs → CDI compact cassettes → CD
Audio signalprocessing
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
restoration of distorted audio signals
I typical artifacts of old recordings:I clicksI tape speed fluctuationsI hum (mains frequency)I noiseI distortions
Audio signalprocessing
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
restoration of distorted audio signals
I aims:I recovery of the original soundI in some cases make improvements with respect to
original soundI e.g. extension of a limited frequency response
I in future: model-based solutionsI detection of sound objectsI re-synthesis of the signal in perfect audio quality
Audio signalprocessing
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
removal of clicks
Audio signalprocessing
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
restoration of distorted audio signals
I removal of clicks:I typical for signals stemming from vinyl discsI strategy:
I detection of the clicksI delete and replace the section by estimated signal
(interpolator)
Audio signalprocessing
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
removal of tape speedvariations
Audio signalprocessing
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
removal of tape speed variations
I removal of tape speed variations (→ pitchvariations):
I typical for signals stemming from tape recordingsI strategy:
I short-time spectral analysis with pitch detectionI with a priori knowledge about the original pitch
→ identification of the time axis distortionI apply inverse time axis distortion
Audio signalprocessing
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
removal of hum
Audio signalprocessing
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
removal of hum
I removal of hum (and possible harmonics):I strategy:
I narrow-band notch filterI problem:
I → notch filter impulse response: pulse at τ = 0and at τ = 10ms
I → addition of a sort of echo → possible audibleartifacts
Audio signalprocessing
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
removal of broad-band noise
Audio signalprocessing
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
removal of broad-band noise
I removal of broad band noise:I typical for all early sound storage mediaI principle:
I establish filter bank with time variableamplification in each band
I if signal is present → reference amplificationI dominating noise → very small amplification
Audio signalprocessing
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
removal of broad-band noise
I strategy:I assumption of constant power spectral density of
the noise componentI estimation of the noise spectrum in signal pauses
(”minimum during the whole piece”)I short-time spectral analysis of the signal →
evaluation of S/NI determine amplification of each spectral line from
S/NI delicate choice of the time constant for the
amplification adaptation
Audio signalprocessing
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
examples
Audio signalprocessing
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
restoration of distorted audio signals:
example
De-Noise
Audio signalprocessing
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
restoration of distorted audio signals:
example
De-Click
Audio signalprocessing
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
restoration of distorted audio signals:
example
Remove Hum
Audio signalprocessing
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
restoration of distorted audio signals:
example
De-Clip
Audio signalprocessing
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
restoration of distorted audio signals:
example
original: originalde-clicking: step 1de-hissing: step 2fadings: step 3
Audio signalprocessing
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
eth-acoustics-2