Presentation on theme: "Sound Quality Assessment IR measurements and AQT"— Presentation transcript:
1 Sound Quality Assessment IR measurements and AQT Universityof ParmaSound Quality Assessment IR measurements and AQT
2 Problems with traditional measurements methods Traditional measurement are based on steady-state signals - they provide a frequency response curve - this does not provide significant match with listening experience in carsIt was attempted to employ transient analysis (impulse response) based on the same parameters employed for concert halls (reverberation time, clarity, definition) - also these do not correspond with the short time scale of time transients inside carsIn-car listening tests are useful, but difficult to standardizeGeneral lack of understanding of the relationship between subjective perception and physical facts
3 SolutionsReliable in-car measurement technique (MLS, sweep)Transient analysis and equalization (AQT)Virtual listening for comparative testsSubjective (IPA) and objective (IPM) evaluation indexes for audio quality assessmentNew metric based on all above for rating with a sigle number the sound quality (IQSB)
4 Methods: Reliable in-car measurement technique Impulse Response (IR) as standard measurement for characterization of the car soundHardware: B&K type 4100 binaural head and torsoHardware: Notebook PC + Edirol FA-101 Firewire interfaceSoftware: Adobe Audition and Aurora for IR measureAQT as advanced analysis (instead of FFT)
5 Standardized Position of the Dummy Head Reliable in-car measurement techniqueStandardized Position of the Dummy Headca. 25o70 cm30 cmverticale volanteverticale a piomboasse del dorso (sul piano dorsale)tettuccio
6 Hardware: PC and audio interface Reliable in-car measurement techniqueHardware: PC and audio interfaceEdirol FA-101Firewire sound card:10 in / 10 out24 bit, 192 kHzASIO and WMA
8 Measurement processThe 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).
9 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.
10 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 requiredTest Signal x(t)Inverse Filter z(t)
16 Post processing of impulse response Specific XFM modules have been developed for the computation of STI and for performing standard analysis according to ISO-3382
17 AQT AnalysisGoal:Substitute classical analysis based on FFT with a new kind of dynamic transient analysisReason:FFT characterizes a only in steady state conditionBUTHearing is more sensible to transientsMusical signal is not a steady state signalSolution:AQT analysis (Acoustic Quality Test)
18 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 responseFind resonances and tails that affect hearingUseful during car development and for design of optimal equalizationOutput:“Dynamic” frequency response curve of the soundArticulation curve (transient capability at each frequency)
19 AQT AnalysisMethods:The test signal is a sequence of sine bursts of increasing frequencyEach burst is 200 ms long. The gap between a burst and the next is 33 msThe instantaneous RMS level is plotted versus time (or frequency)The same result can be also obtained convolving the test signal with the IR
20 AQT AnalysisDetails:The envelope of the maxima is the dynamic frequency response of theThe depth of the valley between two bursts shows the dynamic transient capability of theUniversiy of Parma
21 AQT Analysis Temporal masking according to Zwicker 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.
22 AQT AnalysisAQT Tool:An automatic tool was developed to perform a quick processingThis tool can also generate the coefficients for digital FIR filtersThe filters are designed for producing a prescribed optimal frequency response
23 AQT Equalization results Fiat STILOAbove: measured AQT curve not equalized vs. target curve (red)Below: measured AQT curve after equalization vs. target curve (red)Results (IPA listening test):Not equalizedTraditional FIRInverse AQT22.214.171.124
24 The new AQT plugin for Audition The new module is still under development and will allow for very fast computation of the AQT curve from within Adobe Audition
25 ConclusionsThe sine sweep method revealed to be systematically superior to the MLS method for measuring electroacoustical impulse responsesIn fact, it is now employed from top-grade measurement systemss, includiong the Audio Precision (TM)Traditional FFT-based analysis of the measured impulse response did noy show good correlation with subjective perceptionIt was tehrefore necessary to derive new physical descriptors, better correlating with the human listening experience inside a car.Three physical parametrs revealed to be more correlated with subjective responses: IACC, STI and AQT