Sound Quality Assessment IR measurements and AQT

Sound Quality AssessmentSound Quality AssessmentIR measurements and AQTIR measurements and AQT

Universityof Parma

|| Page 218.05.200618.05.2006 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidential

Problems with traditional measurements methods

Traditional measurement are based on steady-state signals Traditional measurement are based on steady-state signals - they provide a frequency response curve - this does not - they provide a frequency response curve - this does not provide significant match with listening experience in cars provide significant match with listening experience in cars

It was attempted to employ transient analysis (impulse It was attempted to employ transient analysis (impulse response) based on the same parameters employed for response) based on the same parameters employed for concert halls (reverberation time, clarity, definition) - also concert halls (reverberation time, clarity, definition) - also these do not correspond with the short time scale of time these do not correspond with the short time scale of time transients inside carstransients inside cars

In-car listening tests are useful, but difficult to standardizeIn-car listening tests are useful, but difficult to standardize General lack of understanding of the relationship between General lack of understanding of the relationship between

subjective perception and physical factssubjective perception and physical facts


SolutionsSolutions

Reliable in-car measurement technique Reliable in-car measurement technique (MLS, sweep) (MLS, sweep)

Transient analysis and equalization (AQT)Transient analysis and equalization (AQT)Virtual listening for comparative testsVirtual listening for comparative testsSubjective (IPA) and objective (IPM) Subjective (IPA) and objective (IPM) evaluation indexes for audio quality evaluation indexes for audio quality assessment assessment

New metric based on all above for rating New metric based on all above for rating with a sigle number the sound quality with a sigle number the sound quality (IQSB)(IQSB)


Methods:⇨Impulse Response (IR) as standard

measurement for characterization of the car sound

⇨Hardware: B&K type 4100 binaural head and torso

⇨Hardware: Notebook PC + Edirol FA-101 Firewire interface

⇨Software: Adobe Audition and Aurora for IR measure

⇨AQT as advanced analysis (instead of FFT)

Reliable in-car measurement technique



Standardized Position of the Dummy Head

ca. 25o

70 cm

30 cmverticale volante

verticale a piombo

asse del dorso (sul piano dorsale)

tettuccio



Hardware: PC and audio interfaceEdirol FA-101Firewire sound

card:10 in / 10 out

24 bit, 192 kHzASIO and WMA



Software

Aurora PluginsGenerate MLSGenerate MLS

Deconvolve MLSDeconvolve MLS

Generate SweepGenerate Sweep

Deconvolve SweepDeconvolve Sweep

ConvolutionConvolution

Kirkeby Inverse FilterKirkeby Inverse Filter

Speech Transm. IndexSpeech Transm. Index


Measurement process

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). 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) +

output y(t) linear system w(t)h(t)

distorted signal w(t)


Test signal: Log Sine Sweep

x(t) is a sine signal, which frequency is varied exponentially with time, starting at f1 and ending at f2.

1e

ffln

Tf2sin)t(x 1

2ffln

Tt

1

2

1


Deconvolution of Log 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

Test Signal x(t) Inverse Filter z(t)


Test Signal – x(t)


Measured signal - y(t)

The not-linear behaviour of the loudspeaker causes many harmonics to appearThe not-linear behaviour of the loudspeaker causes many harmonics to appear


Inverse Filter – z(t)

The deconvolution of the IR is obtained convolving the measured signal y(t) with the inverse filter z(t) [equalized, The deconvolution of the IR is obtained convolving the measured signal y(t) with the inverse filter z(t) [equalized, time-reversed x(t)]time-reversed x(t)]


Result of the deconvolution

The last impulse response is the linear one, the preceding are the harmonics distortion products of various orders

1°2°3°

5°


Maximum Lenght Sequence vs. Sweep


Post processing of impulse response

Specific XFM modules have been developed for the computation of STI and Specific XFM modules have been developed for the computation of STI and for performing standard analysis according to ISO-3382for performing standard analysis according to ISO-3382


Goal:⇨Substitute classical analysis based on FFT with a new

kind of dynamic transient analysis Reason:

⇨FFT characterizes a only in steady state condition BUT

⇨Hearing is more sensible to transients ⇨Musical signal is not a steady state signal

Solution:⇨AQT analysis (Acoustic Quality Test)

AQT Analysis


Features:⇨Use transient stimulus (wavelet) instead of steady-

state (periodic sine)⇨Find a frequency response curve more related to

perceived curve than FFT response⇨Find resonances and tails that affect hearing⇨Useful during car development and for design of

optimal equalizationOutput:

⇨“Dynamic” frequency response curve of the sound ⇨Articulation curve (transient capability at each

frequency)

AQT Analysis


Methods:⇨The test signal is a

sequence of sine bursts of increasing frequency

⇨Each burst is 200 ms long. The gap between a burst and the next is 33 ms

⇨The instantaneous RMS level is plotted versus time (or frequency)

⇨The same result can be also obtained convolving the test signal with the IR

AQT Analysis

|| Page 2018.05.200618.05.2006 Angelo FarinaAngelo Farina UNIPR / ASK IndustriesUNIPR / ASK Industries || A All Rights Reservedll Rights Reserved || ConfidentialConfidentialUniversiy of

Parma

Details:⇨ The envelope of

the maxima is the dynamic frequency response of the

⇨ The depth of the valley between two bursts shows the dynamic transient capability of the

AQT Analysis


AQT Analysis

The analysis of a single burst shows the level variation due to a single burst, and the overshoot phenomenon at the beginning and end of the burst.

Temporal masking according to Zwicker


AQT Tool:⇨An automatic

tool was developed to perform a quick processing

⇨This tool can also generate the coefficients for digital FIR filters

AQT Analysis

The filters are designed for producing a prescribed optimal

frequency response


Fiat STILO

Above: measured AQT curve not equalizedvs. target curve (red)

Below: measured AQT curve after equalization vs. target curve (red)

Results (IPA listening test):

AQT Equalization results

Not equalizedNot equalized Traditional Traditional FIRFIR

Inverse AQTInverse AQT

7.187.18 7.207.20 7.507.50


The new AQT plugin for Audition

The new module is still under development and will allow for very fast The new module is still under development and will allow for very fast computation of the AQT curve from within Adobe Auditioncomputation of the AQT curve from within Adobe Audition


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

the MLS method for measuring electroacoustical impulse the MLS method for measuring electroacoustical impulse responsesresponses

In fact, it is now employed from top-grade measurement systemss, In fact, it is now employed from top-grade measurement systemss, includiong the Audio Precision (TM) includiong the Audio Precision (TM)

Traditional FFT-based analysis of the measured impulse response Traditional FFT-based analysis of the measured impulse response did noy show good correlation with subjective perceptiondid noy show good correlation with subjective perception

It was tehrefore necessary to derive new physical descriptors, It was tehrefore necessary to derive new physical descriptors, better correlating with the human listening experience inside a car.better correlating with the human listening experience inside a car.

Three physical parametrs revealed to be more correlated with Three physical parametrs revealed to be more correlated with subjective responses: IACC, STI and AQTsubjective responses: IACC, STI and AQT

Sound Quality Assessment IR measurements and AQT

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