Energy Envelope

Angelo Farina Angelo Farina

Industrial Engineering Dept.

Industrial Engineering Dept.

University of Parma

University of Parma - - ITALY ITALY

La misura della risposta all'impulso La misura della risposta all'impulso

per la caratterizzazione di sistemi per la caratterizzazione di sistemi

acustici e vibrazionali acustici e vibrazionali

Strumenti e metodi di misura per l’acustica e le vibrazioni

Seminario in ricordo di Eugenio Mattei

Ancona, 21 settembre 2008

ƒ Traditional time-domain measurements with pulsive sounds and omnidirectional transducers

ƒ MLS and TDS methods for electroacoustical masurements

The The Past Past

The The Present Present

Time Line

ƒ Electroacoustical measurements employing the Exponential Sine Sweep method (ESS)

ƒ Capturing spatial information with multichannel microphones

ƒ Post processing of measured IRs for computing acoustical

parameters and for auralization

The The Past Past

Starting

Starting point point : : room room impulse impulse response response

Omnidirectional receiver Direct Sound

Reflected Sound

Point Source

Direct Sound

Traditional

Traditional measurement measurement methods methods

Example

Example of of a a pulsive pulsive impulse impulse response response

Loudspeaker

Loudspeaker as as sound source sound source

ƒ ƒ A A loudspeaker loudspeaker is is fed fed with with a a special special test test signal signal x(t), x(t), while

while a microphone a microphone records records the room the room response response

ƒ ƒ A A proper proper deconvolution deconvolution technique technique is is required required for for

Portable PC with 4- channels sound board Original Room

SoundField Microphone

B- format 4- channels signal

(WXYZ)

Measurement of B- format Impulse Responses

MLS excitation signal

Portable PC with additional sound card Room

Microphone

Output signal y Measurement of Room

Impulse Response

MLS test signal x Loudspeaker

Measurement process

ƒ The desidered result is the linear impulse response of the acoustic propagation h(t). It can be recovered by knowing the test signal x(t) and the measured system output y(t).

ƒ It is necessary to exclude the effect of the not-linear part K and of the background noise n(t).

Not-linear, time variant

system K[x(t)]

Noise n(t)

input x(t)

+

w(t)⊗h(t) distorted signal

w(t)

Electroacoustical

Electroacoustical methods methods

ƒ ƒ Different Different types types of of test signals test signals have have been been developed developed , , providing

providing good good immunity immunity to to background noise background noise and easy and easy deconvolution

deconvolution of of the the impulse impulse response response : :

►

MLS (Maximum Lenght Sequence, pseudo-random white noise)

►

TDS (Time Delay Spectrometry, which basically is simply a linear sine sweep, also known in Japan as “stretched pulse” and in Europe as “chirp”)

►

ESS (Exponential Sine Sweep)

ƒ ƒ Each Each of of these these test signals test signals can be can be employed employed with with different different deconvolution

deconvolution techniques, techniques , resulting resulting in a number in a number of of

“different “ different” ” measurement measurement methods methods

ƒ ƒ Due Due to to theoretical theoretical and and practical practical considerations considerations , the , the preference

preference is is nowadays nowadays generally generally oriented oriented for for the the usage usage of of

The first MLS

The first MLS apparatus apparatus - - MLSSA MLSSA

More

More recently recently - - the CLIO system the CLIO system

The first TDS

The first TDS apparatus apparatus - - TEF TEF

ƒ ƒ Techron Techron TEF 10 was TEF 10 was the first apparatus the first apparatus for for measuring measuring impulse impulse responses responses with with TDS TDS

ƒ ƒ Subsequent Subsequent versions versions (TEF 20, TEF 25) also (TEF 20, TEF 25) also support support MLS MLS

Theory

Theory of of MLS MLS method method

ƒ ƒ X(t) is X(t) is a periodic a periodic binary binary signal

signal obtained obtained with with a a suitable

suitable shift- shift -register register, , configured

configured for for maximum

maximum lenght lenght of of the the period

period. .

N stages

XOR k stages

x’(n)

1 2

L = ^N −

MLS MLS deconvolution deconvolution

ƒ ƒ The The re re - - recorded recorded signal signal y(i) y(i) is is cross cross - - correlated correlated with with the the excitation

excitation signal signal thanks thanks to to a fast Hadamard a fast Hadamard transform. The transform . The result

result is is the the required required impulse impulse response response h(i), if h(i), if the system the system was was linear linear and time and time- -invariant invariant

y 1 M

L h 1

~ ⋅ + ⋅

=

z Where M is the Hadamard matrix, obtained by permutation of the original MLS sequence m(i)

( )

[ ^{i j 2 mod L} ] ¹

m )

j , i (

M ~ = + − −

MLS MLS example example

Portable PC with 4- channels sound board Original Room

SoundField Microphone

B-format 4- channels signal Measurement of B-format

Impulse Responses

MLS excitation signal

Portable PC with additional sound card Room

Microphone

Output signal y Measurement of Room

Impulse Response Loudspeaker

MLS test signal x

MLS MLS example example

Example

Example of of a MLS a MLS impulse impulse response response

The The Present Present

Edirol FA-101 Firewire sound

card:

10 in / 10 out 24 bit, 192 kHz ASIO and WDM

Today’s Hardware: PC and audio interface

Hardware:

Hardware: loudspeaker loudspeaker & & microphone microphone

Dodechaedron loudspeaker

Soundfield

microphone

Aurora Plugins

Generate MLS Generate MLS Deconvolve DeconvolveMLSMLS Generate Sweep Generate Sweep Deconvolve

DeconvolveSweepSweep Convolution

Convolution Kirkeby

KirkebyInverse FilterInverse Filter Speech

Speech TransmTransm. Index. Index

The first ESS system - AURORA

Exponential Sine Sweep method

ƒ x(t) is a band-limited sinusoidal sweep signal,

which frequency is varied exponentially with time, starting at f ₁ and ending at f ₂ .

⎥ ⎥

⎥ ⎥

⎦

⎤

⎢ ⎢

⎢ ⎢

⎣

⎡

⎟⎟

⎟ ⎟

⎠

⎞

⎜⎜

⎜ ⎜

⎝

⎛

−

⋅

⎟⎟ ⎠

⎜⎜ ⎞

⎝

⎛

⋅

⋅ π

= ⋅ ^{⎟⎟ ⎠}

⎜⎜ ⎞

⎝

⋅ ⎛

1 e

f ln f

T f

sin 2 )

t (

x ¹

2

f ln f T

t

1

2

1

Test Signal – x(t)

Stop Stop

Measured signal - y(t)

Stop Stop

Inverse Filter – z(t)

Stop Stop

Deconvolution of Exponential Sine Sweep

The “time reversal mirror” technique is employed: the

system’s impulse response is obtained by convolving

the measured signal y(t) with the time-reversal of the

test signal x(-t). As the log sine sweep does not have

a “white” spectrum, proper equalization is required

Deconvolution

Deconvolution = rotation of the = rotation of the sonograph sonograph

Linear

Linear

2 2 ^{nd nd} order order

Result of the deconvolution

2° 1°

5° 3°

IR IR Selection Selection

ƒ ƒ After After the sequence the sequence of of impulse impulse responses responses has has been been obtained, obtained , it it is is possible possible

to to select select and and insulate insulate just just one one of of them: them :

Maximum Length Sequence vs. Exp. Sine Sweep

Example

Example of of an an ESS ESS impulse impulse response response

Post processing of impulse responses

ƒ ƒ A special A special plugin plugin has has been been developed developed for for the computation the computation of of STI according STI according

to to IEC- IEC -EN 60268 EN 60268- -16:2003 16:2003

The STI

The STI Method Method

The STI method is based on the MTF concept: a carrier signal (one-octave-band-filtered noise) is amplitude

modulated at a given modulation frequency with 100%

En er g y En v el o p e

Acoustic system

1/F 1/F

time time

MTF from Impulse Response MTF from Impulse Response

ƒ ƒ It It is is possible possible to to derive the MTF values derive the MTF values from from a a single

single impulse impulse response response measurement measurement : :

( ) ( )

∫ ( )

∫

∞

∞

⋅

⋅

⋅

⋅

⋅

⋅

−

⋅

=

2 0

2

exp 2

) (

τ τ

τ τ

π τ

d h

d F

j h

F m

f

To compute each value of m(F) from the impulse response h(t), an octave-band filter is first applied to the impulse response, in order to select the carrier’s frequency band f.

Then m(F) is obtained with the formula

Background

Background noise noise

ƒ ƒ If If the background the background noise noise is is superposed superposed to to the the impulse impulse response

response , the , the previous previous method method already already takes takes care of care of it, and it , and the MTF

the MTF values values are measured are measured correctly correctly

ƒ ƒ However, in some However , in some cases cases , it , it is is advisable advisable to to perform perform a noise a noise- - free free measurement measurement of of the IR, and the IR, and then then insert insert the the effect effect of of the the noise

noise with with the following the following expression: expression :

⎟⎟ ⎠

⎜⎜ ⎞

⎝

⎛ −

+

⋅

=

10 10

1 ) 1 (

' )

(

signal noise

L

F L

m F

m

Post processing of impulse responses

ƒ ƒ A special A special plugin plugin has has been been developed developed for for performing performing analysis analysis of of acoustical acoustical parameters

parameters according according to to ISO- ISO -3382 3382

The new AQT plugin for Audition

ƒ ƒ The new The new module module is is still still under development under development and will and will allow allow for for very very fast fast computation

computation of of the AQT (Dynamic the AQT ( Dynamic Frequency Frequency Response Response ) curve from ) curve from within within Adobe

Adobe Audition Audition

Distortion measurements Distortion measurements

ƒ ƒ A headphone was driven A headphone was driven with a 1 V RMS signal, with a 1 V RMS signal,

causing severe causing severe

distortion in the small distortion in the small

loudspeaker.

loudspeaker.

ƒ ƒ The measurement was The measurement was made placing the

made placing the

headphone on a dummy headphone on a dummy

head.

head.

ƒ ƒ Measurements: ESS and Measurements: ESS and

traditional sine at 1 kHz

traditional sine at 1 kHz

Distortion measurements

Distortion measurements

Spatial

Spatial analysis analysis by by directive directive impulse impulse responses responses

ƒ ƒ The initial The initial approach approach was was to to use use directive directive microphones microphones for for gathering gathering some some information

information about about the spatial the spatial properties properties of of the sound the sound field field “as “ as perceived perceived by by the listener the listener” ”

ƒ ƒ Two Two apparently apparently different different approaches approaches emerged: emerged : binaural binaural dummy dummy heads heads and and pressure

pressure- -velocity velocity microphones: microphones :

Binaural Binaural microphone

microphone (left ( left ) ) and and

Pressure

Pressure -velocity - velocity microphone

microphone (right) (right)

IACC

IACC “ “ objective objective ” ” spatial spatial parameter parameter

ƒ ƒ It It was was attempted attempted to to “quantify “ quantify” ” the “ the “spatiality spatiality” ” of of a room a room by by means means of of

“objective “ objective” ” parameters, parameters , based based on 2- on 2 -channels channels impulse impulse responses responses measured measured with with directive directive microphones microphones

ƒ ƒ The most The most famous famous “spatial “ spatial” ” parameter parameter is is IACC (Inter Aural IACC (Inter Aural Cross Cross Correlation

Correlation), ), based based on binaural on binaural IR measurements IR measurements

LeftLeft

Right Right

80 ms 80 ms

pp_LL(τ(τ))

pp_RR((ττ))

ms 80

Lateral

Lateral Fraction Fraction (LF) (LF) spatial spatial parameter parameter

ƒ ƒ Another Another “spatial “ spatial” ” parameter parameter is is the Lateral the Lateral Fraction Fraction LF LF

ƒ ƒ This This is is defined defined from from a 2- a 2 -channels channels impulse impulse response, the first response , the first channel channel is is a a standard

standard omni omni microphone microphone , the second , the second channel channel is is a a “figure “ figure- -of of- -eight eight ” ” microphone

microphone: :

Figure Figure

of of 88 OmniOmni

∫ ( ) ^{τ ⋅ τ}

=

ms 5

82

d

h LF

hh_oo(τ(τ))

hh₈₈((ττ))

Are Are binaural binaural measurents measurents reproducible reproducible ? ?

ƒ ƒ Experiment Experiment performed performed in anechoic in anechoic room room - - same same loudspeaker loudspeaker , same , same source source

and receiver and receiver positions, 5 positions , 5 binaural binaural dummy dummy heads heads

Are IACC

Are IACC measurents measurents reproducible reproducible ? ?

ƒ ƒ Diffuse field Diffuse field - - huge huge difference difference among among the 4 dummy the 4 dummy heads heads

IACCe - random incidence

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

IACCe

B&K4100 Cortex Head Neumann

Are LF

Are LF measurents measurents reproducible reproducible ? ?

ƒ ƒ Experiment Experiment performed performed in the Auditorium of in the Auditorium of Parma - Parma - same same loudspeaker, loudspeaker ,

same same source and receiver source and receiver positions, 4 positions , 4 pressure- pressure -velocity velocity microphones microphones

Are LF

Are LF measurents measurents reproducible reproducible ? ?

ƒ ƒ At 25 m distance At 25 m distance, the , the scatter scatter is is really really big big

Comparison LF - measure 2 - 25m distance

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

LF

Schoeps Neumann Soundfield B&K

3D 3D Impulse Impulse Response Response ( ( Gerzon Gerzon , 1975) , 1975)

Portable PC with 4- channels sound board Original Room

Sound Source

SoundField Microphone

B-format 4-channels signal (WXYZ) Measurement of B-format

Impulse Responses

MLS or sweep excitation signal

Sound Source

Mono Mic.

B-format Imp. Resp.

of the original room

B-format 4-channels signal (WXYZ) Convolver

Ambisonics decoder

3D extension 3D extension of of the the pressure- pressure -velocity velocity measurements measurements

ƒ ƒ The Soundfield The Soundfield microphone microphone allows allows for for simultaneous simultaneous measurements measurements of of the the omnidirectional

omnidirectional pressure pressure and of and of the three the three cartesian cartesian components components of of particle particle velocity

velocity (figure- (figure -of of- -8 8 patterns patterns) )

Directivity

Directivity of of transducers transducers

Soundfield

Soundfield ST- ST -250 250 microphone microphone

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

0

30

60

90

120

150 180

210 240 270

300 330

125 Hz

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

0

30

60

90

120

150 180

210 240 270

300 330

250 Hz

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

0

30

60

90

120

150 180

210 240 270

300 330

500 Hz

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

0

30

60

90

120

150 180

210 240 270

300 330

1000 Hz

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

0

30

60 300

330

2000 Hz

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

0

30

60 300

330

4000 Hz

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

0

30

60 300

330

8000 Hz

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

0

30

60 300

330

16000 Hz

A A - - format format microphone microphone arrays arrays

ƒ ƒ Today Today several several alternatives alternatives to to Soundfield Soundfield microphones microphones do exists do exists. . All All of of them them are providing are providing “raw “ raw” ” signals signals from from the 4 capsules the 4 capsules, and the , and the conversion conversion from from these

these signals signals (A ( A- -format format) ) to to the standard Ambisonic the standard Ambisonic signals signals (B ( B- -format format) ) is is performed

performed digitally digitally by by means means of of software running software running on the computer on the computer

The The Waves Waves project (2003) project (2003)

ƒ ƒ The original The original idea of idea of Michael Gerzon Michael Gerzon was was finally finally put in practice put in practice in 2003, in 2003, thanks

thanks to to the Israeli the Israeli -based - based company WAVES company WAVES

ƒ ƒ More than More than 50 theatres 50 theatres all all around around the world were the world were measured, measured , capturing capturing 3D 3D IRs IRs (4 (4 -channels - channels B B -format - format with with a Soundfield a Soundfield microphone) microphone )

ƒ ƒ The measurments The measurments did did also also include binaural include binaural impulse impulse responses, and a responses , and a circular

circular- -array array of of microphone microphone positions positions

ƒ ƒ More details More details on WWW.ACOUSTICS.NET on WWW.ACOUSTICS.NET

The The Ciresa Ciresa project (2005) project (2005)

ƒ ƒ Measurements Measurements of of the vibrations the vibrations and and radiated radiated sound from sound from wood wood panels panels

ƒ ƒ Mapping Mapping of of harmonic harmonic tables tables by by means means on an on an XY scanner XY scanner

ƒ ƒ Pressure Pressure measured measured by by means means of of a linear a linear microphone microphone array array

ƒ ƒ Velocity Velocity measured measured by by means means of of a laser vibrometer a laser vibrometer

10 20 30 40 50 60 70 80

1359 Hz

10 20 30 40 50 60 70 80

1312 Hz

Conclusions Conclusions

ƒ ƒ The sine The sine sweep sweep method method revealed revealed to to be be systematically systematically superior

superior to to the MLS & TDS methods the MLS & TDS methods for for measuring measuring electroacoustical

electroacoustical impulse impulse responses responses

ƒ ƒ The ESS The ESS method method also also allows allows for for measurement measurement of of not not - - linear

linear devices devices and to and to assess assess harmonic harmonic distortion distortion

ƒ ƒ Current Current limitation limitation for for spatial spatial analysis analysis in in room room acoustis acoustis is is due due to to transducers transducers ( ( loudspeakers loudspeakers and and

microphones microphones) )

ƒ ƒ A A new new generation generation of of loudspeakers loudspeakers and and microphones microphones , , made made of of massive massive arrays arrays , is , is under development under development . .

ƒ ƒ