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Sound Quality of Audio Systems

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Sound Quality of Audio Systems Loudspeaker Data – Reliable, Comprehensive, Interpretable Introduction Biography: 1977-1982 Study Electrical Engineering, TU Dresden 1982-1990 R&D Engineer VEB RFT, Leipzig, 1992-1993 Scholarship at the University Waterloo (Canada) 1993-1995 Harman International, USA 1995-1997 Consultancy 1997 Managing the KLIPPEL GmbH 2007 Professor for Electro-acoustics, TU Dresden My interests and experiences: • electro-acustics, loudspeakers • digital signal processing applied to audio Wolfgang Klippel • psycho-acoustics and measurement techniques Klippel GmbH Agenda Left Right Audio Audio Channel Channel Audio-System Transducer Perception (Transducer, DSP, (woofer, tweeter) Final Audio Application Amplifier) (Room, Speaker, Listening Position, Stimulus) 1. Perceptual and physical evaluation at the listening point perceptive modeling & sound quality assessment auralization techniques & systematic listening tests 2. Output-based evaluation of (active) audio systems holografic near field measurement of 3D sound output prediction of far field and room interaction nonlinear distortion at max. SPL 3. Comprehensive description of the passive transducer parameters (H(f), T/S, nonlinear, thermal) symptoms (THD, IMD, rub&buzz, power handling) 3 Objectives Left Right Audio Audio Channel Channel Audio-System Transducer Perception (Transducer, DSP, (woofer, tweeter) Final Audio Application Amplifier) (Room, Speaker, Listening Position, Stimulus) • clear definition of sound quality in target application • filling the gap between measurement and listening • numerical evaluation of design choices • meaningful transducer data for DSP and system design • selection of optimal components • maximal performance-cost ratio • smooth communication between customer and supplier 4 Objective Methods for Assessing Loudspeakers Room Loudspeaker Parameter-Based Parameters Parameters Method e.g. T/S parameter, amplitude and phase response, nonlinear and thermal parameters Loudspeaker- Psychoacoustical Stimulus Room Model Model Sensations nonlinear nonlinear e.g. music, test signals Distortion Perceptual Measurement Quality Method e.g. THD, IMD, rub&buzz e.g. predicted distortion preference 5 Perceptual Evaluation of Signal Distortion distortion Ideal reference Basic Conceptions signal monaural processing Basic Auditory test signal Sensations Loudness Perceived Binaural Fluctuations Defects Processing Sharpness S DS Overall stimulus + Coloration V DV Quality Loss Spaciousness R DR test signal Localization Basic reference Perceived defects consider the signal monaural ideal conceptions and the impact processing on quality distortion The basic auditory sensations are the dimensions of the perceptional space and describe the audibility of the distortion 7 Auralization of Signal Distortion Input Output Signal Signal u (t ) es 0 p(t) Linear dlin (t) OBJECTIVES: Model Linear 1. Virtual enhancement or Distortion attenuation of distortion n(t) components Nonlinear dnlin (t) Model Nonlinear Distortion 2. Systematic Listening Tests Noise 3. Defining a value S in d (t) DIS Unpredictable irr dB describing the Dynamics Irregular Distortion distance to the audibilty Model threshold 10 Finding Audibility Thresholds histogram of the audibility thresholds of 55000 participants of a listening test at www.klippel.de weighted up and down method low distortion audibility threshold SDIS enhancement attenuation SDIS=-15 dB 11 Subjective and Objective Evaluation Objective Subjective Engineering Evaluation Evaluation Marketing Management Listening Test + Auralization Perceptive Modeling SDIS Physical Data • Distortion, Maximal Output Audibility of distortion • Displacement, Temperature Perference, • Evaluation of Design Choices • Defining target specification • Clues for Improvements • Tuning to the market Performance/cost ratio 13 Agenda Left Right Audio Audio Channel Channel Audio-System Transducer Perception (Transducer, DSP, (woofer, tweeter) Final Audio Application Amplifier) (Room, Speaker, Listening Position, Stimulus) 1. Perceptual and physical evaluation at the listening point perceptive modeling & sound quality assessment auralization techniques & systematic listening tests 2. Output-based evaluation of (active) audio systems holografic near field measurement of 3D sound output prediction of far field and room interaction nonlinear distortion at max. SPL 3. Comprehensive description of the passive transducer parameters (H(f), T/S, nonlinear, thermal) symptoms (THD, IMD, rub&buzz, power handling) 14 Evaluation of the Audio Product Measurement in Target Application Measurement under Standard Condition (Standard) living room Anechoic room Suppressing the considering room, influence of distance, ambient acoustical noise and other transfer of the environment conditions audio system P P U U S S H H I I I P 0 C C P P W P P U U R 1 2 S S O O H H U U MIC1 LINE2 T T LINE1 MIC2 1 2 I I I P 0 C C W P P R 1 2 O O U U MIC1 LINE2 T T LINE1 MIC2 1 2 Definition of target performance as Physical characteristics perceived by final (comprehensive, simple user to interpret, comparable, reproducible) Auralization/Listening Test Loudspeaker Development Perceptual Evaluation 15 Characteristics defined by IEC 60268-5 1. Impedance (rated value, Z(f)-curve, Qts, Vas) 2. Input voltage (rated noise, short + long term maximal) 3. Input power (rated noise, short + long term maximal) 4. Frequency characteristics (rated range, fs, fvent) 5. SPL in stated band, sensitivity for 1 W 6. SPL response for voltage, H(f), effec. freq. range 7. Output (acoustic) power, efficiency 8. Directivity (pattern, rad. angle, index, coverage) 9. Amplitude nonlinearity (THD, IMD) The scope of this standard is limited to passive loudspeaker systems ! 16 Active Loudspeaker Systems Properties of the black box depend on control parameters and stimulus Sound Field digital audio Black box Near Field Far Field stream No access to internal states Evaluation is based on evaluation of drivers acoustical output control parameters (e.g. attenuation) 17 IEC 60268-5 applicable to Active Systems ? can be applied, need modification, not applicable 1. Impedance (rated value, Z(f)-curve, Qts, Vas) 2. Input voltage (rated noise, short + long term maximal) 3. Input power (rated noise, short + long term maximal) 4. Frequency characteristics (fs, fvent) 5. SPL in stated band, Sensitivity for 1 W 6. SPL response for voltage input, H(f), effec. freq. range, 7. Output (acoustic) power, efficiency 8. Directivity (pattern, rad. angle, index, coverage) 9. Amplitude nonlinearity (THD, IMD) 18 Modern Audio Systems New Requirements: • Audio systems become active no access to the electrical terminals of the transducer digital signal processing dedicated to the transducer amplifiers with more capabilities • Audio systems become portable main axis of radiation, sweet point and position of the listener are not defined battery powered • Audio systems become personal (hand-hold devices) listener is in the near field of the source • Audio systems become smaller, lighter using green transducer technologies (efficient, nonlinear) 19 Integration of DSP, power amplification and electro-acoustical conversion amplifiers Nonlinear components DSP protection Tweeter Digital protection Equalizer audio Limiter X-over linearization input Midrange Gain protection Control linearization Woofer drivers Control input • Smart technologies (DSP) saves hardware resources and energy • more acoustical output at reduced weight, size and cost Green Speaker Technology 20 New Standards required for Evaluating Active and Passive Loudspeaker Systems • Applicable to active and passive systems (prototypes, final and competitive products) • Describing the radiated direct sound at any point within the listening area (including near field) • Consideration of room-loudspeaker interaction • Assessment of maximal acoustical output • Irregular loudspeaker defects (rub, buzz, leakage, particles, loose connections) • Comprehensive set of data (low redundancy, easy interpretation) • Bridging QC and R&D • Bridging perceptive and physical evaluation Currently discussed in standard committees 21 Small Signal Performance Specifications for Active and Passive Loudspeaker Systems • On-Axis Sound Pressure at reference distance rref=1m SPL(f) response Phase response (group delay (f) response) • Directivity a) single-value characteristics sound power response Pa(f) directivity index Di(f) b) 2D far-field data pressure distribution p(θ, ) on a spherical surface at large distance from the source p(θ, ) (balloon plot, beam pattern) c) 3D near/far-field data new sound pressure p(θ, , r ) at any point r in the space beyond the sound source (spherical wave expansion) 22 2D far-field data SPL 4.1 kHz at distance r=4m 6.1 kHz at distance r=4m 90° on-axis 270° azimutal angle azimutal 180° 0° frequency 90° -90° Balloon Plot Beam Pattern Distance r >> dimensions d of the loudspeaker Distance r >> wavelength 23 Complete 3D Information Required Sound Pressure at 7.6 kHz In the following application the listerner is far field data closely located to the source: are less important • personal audio equipment (smart phone) • multimedia (tablet, notebook) • studio-monitor Near Field • car audio loudspeaker 24 Holografic Measurement of the radiated direct sound in the complete 3D space 1. Scanning the sound pressure in the near field of the source 2. Expansion in spherical waves Loudspeaker microphone monopol z dipols r quadropols Hankel function N n (2) m φ pout (r,,,) cn,m ()hn (kr)Yn (,) n0 mn Coefficients
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