Acoustical Measurement of Sound System Equipment ......Setup for IMD in Sound Pressure bass sweep...
Transcript of Acoustical Measurement of Sound System Equipment ......Setup for IMD in Sound Pressure bass sweep...
KLIPPEL LIVE #9: Intermodulation Distortion, 1
Acoustical Measurement
of Sound System Equipment
according IEC 60268-21
KLIPPEL LIVE
a series of webinars presented by
Wolfgang Klippel
KLIPPEL LIVE #9: Intermodulation Distortion, 2
1. Modern audio equipment needs output based testing
2. Standard acoustical tests performed in normal rooms
3. Drawing meaningful conclusions from 3D output measurement
4. Simulated standard condition at an evaluation point
5. Maximum SPL – giving this value meaning
6. Selecting measurements with high diagnostic value
7. Amplitude Compression – less output at higher amplitudes
8. Harmonic Distortion Measurements – best practice
9. Intermodulation Distortion – music is more than a single tone
10. Impulsive distortion - rub&buzz, abnormal behavior, defects
11.Benchmarking of audio products under standard conditions
12.Auralization of signal distortion – perceptual evaluation
13.Setting meaningful tolerances for signal distortion
14.Rating the maximum SPL value for a product
15.Smart speaker testing with wireless audio input
Acoustical testing of a modern active audio device
Previous Sessions
KLIPPEL LIVE #9: Intermodulation Distortion, 3
9th KLIPPEL LIVE:
互调失真 – 音乐不仅仅是单音Intermodulation Distortion – music is more than a single tone
今日话题 Topics today:
• 互调失真的物理原因 Physical causes for intermodulation distortion
• 符合IEC标准60268-21的测量 Measurements according to IEC Standard 60268-21
• 使用双音激励的测试 Testing with a two-tone stimulus
• 使用多音复合激励的测试 Testing with a multi-tone complex
• 结果的解读 Interpretation of the results
• 实际演示 Practical demos
KLIPPEL LIVE #9: Intermodulation Distortion, 4
Poll:
您是否评估互调失真?Do you evaluate the intermodulation distortion ?
A. 否 No
B. 是,通过听音乐 Yes, by listening to music
C. 是,通过使用双音激励 Yes, by using a two tone stimulus
D. 是,通过使用多音复合 Yes, by using a multi-tone complex
E. 是,使用其他方法 Yes, by other ways
KLIPPEL LIVE #9: Intermodulation Distortion, 5
音乐中的Bl失真Bl-Distortion in Music
未失真音乐信号 Undistorted music signal
需要高位移 → 信号低于fs → 低音信号 High displacement required → signal below fs → bass signal
如果fs < 100 Hz,音频带中的互调信号产生粗糙度Intermodulation with signal in audioband generate roughness when fs < 100 Hz
对音质有很高影响 High impact on sound quality
仅Bl(x) 产生的失真 Distortion generated by Bl(x) only
displacement
intermodulation
Harmonics
KLIPPEL LIVE #9: Intermodulation Distortion, 6
What causes the IM Distortion ?
pre-filterH1,1(f)
1st state variable
multiplier
distortion
fsVoltagesound
pressurehighpass
Static Nonlinearity
pre-filterH1,2(f)
post-filterH2(f)
2nd state variable
广义信号流模型 Generalized Signal Flow Model
描述一个分离的非线性 describing a separated nonlinearity
两个不同状态变量的相乘会产生独特的互调失真!The multiplication of two different state variables generates unique intermodulation distortion !
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Causes for high IM-Distortion
NONLINEARITY
INTERPRETATION
PRE-FILTER
H1,1(f) (output)
PRE-FILTER
H1,2(f) (output)
Stiffness Kms(x) of the suspension
restoring force Low-pass
(displacement x)
Low-pass
(displacement x)
Force factor Bl(x) electro-dynamical force Band-stop
(current i)
Low-pass
(displacement x) nonlinear damping Band-pass
(velocity v)
Low-pass
(displacement x)
Inductance Le(x) self-induced voltage Band-stop
(current i)
Low-pass
(displacement x) reluctance force Band-stop
(current i)
Band-stop
(current i) Inductance Le(i) varying permeability Band-stop
(current i)
Band-stop
(current i)
Mechanical resistance Rms(v)
nonlinear damping Band-pass
(velocity v)
Band-pass
(velocity v)
Young’s modulus E()
of the material cone vibration Band-pass
(strain ) Band-pass
(strain ) Speed of sound c(p) nonlinear sound propagation
(wave steepening) High-pass
(sound pressure p)
High-pass
(sound pressure p)
Time delay τ(x) nonlinear sound radiation
(Doppler effect) High-pass
(sound pressure p)
Low-pass
(displacement x)
Negligible THD
Negligible THD
Negligible THD
f >2fs
测量互调失真很重要 Measurements of Intermodulation Distortion is important !
KLIPPEL LIVE #9: Intermodulation Distortion, 8
Sparse but Comprehensive Stimulus
Stimuli
Single-
Tone
Two-
Tone
Multi-
ToneNoise Audio
Signal
complexity
Spectral Analysis
Total Distortion
2nd-order
3rd-order
Amplitude Phase
Intermodulation Distortion
Harmonics of the two tones
KLIPPEL LIVE #9: Intermodulation Distortion, 9
Intermodulation distortiongenerated by Two-tone Stimulus
difference tones summed tonesharmonics
frequency
Amplitudesound pressure spectrum
Intermodulation
Distortion3rd 3rd
nth
12 )1( fnf −−
nth
12 )1( fnf −+
2nd2nd
12 ff − 12 ff +
3rd
2nd
12 f
nth
1nf
“bass tone”
1f“voice tone”
2f
简化各分量的识别 To simplify the identification of the components:
• 激励音f1和f2之间保持较大距离 Keep large distance between the exciting tones f1 and f2
KLIPPEL LIVE #9: Intermodulation Distortion, 10
IM-Distortion (two-tone signal)Definitions according IEC 60268-21
Second-order Modulation
(FM + AM)
2 1 2 12
2
( ) ( )20 lg
( )IMD
p f f p f fL
p f
− + +=
Third-order Modulation
(FM + AM)
2 1 2 13
2
( 2 ) ( 2 )20 lg
( )IMD
p f f p f fL
p f
− + +=
Total Modulation Distortion
(FM+ AM)
2
2 1 2 1
1
1 2
2
( ) ( )
( , ) 20 lg( )
k
TIMD
p f kf p f kf
L f fp f
=
− + +
=
IEC60268-21中使用相对指标(IMD分量除以载波)The IEC 60268-21 uses relative measures (IMD component divided by carrier )
相对IMD类似于等效输入失真,因为频率距离|f2-f1| << f2The relative IMD are similar to the equivalent input distortion because the frequency distance |f2-f1| << f2
→可使用近场测量提高SNR Near field measurement can be used to improve SNR
KLIPPEL LIVE #9: Intermodulation Distortion, 11
2阶和3阶分量在整个互调失真中的贡献量Contribution of 2nd and 3rd-order Components
to the total intermodulation distortion
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Modulation distortion (U1=1 V)
dB
Frequency f1 [Hz]
Ld2 Ld3 Ldm (cumul)
Total modulation
3rd order2nd order
KLIPPEL LIVE #9: Intermodulation Distortion, 12
Sweeping the Two-Tone SignalHow to choose the frequencies ?
f1 f2
f1 f2
f1 f2
sweeping voice tone
sweeping bass tone
difference tone
measurement
f1 f2
f2-
f1=const.
f1=const.
f2=const.
Sweeping two tones
f2/f1=const.
not very usefulExploit information for f2 f1 !!!
f1
f2
20 kHz
20 kHz
20 Hz
20 Hz
f2/f1=co
nst.
KLIPPEL LIVE #9: Intermodulation Distortion, 13
Poll:
您是如何设置测试激励中双音的频率的?How do you set the frequencies of the two tones in the stimulus for the testing ?
A. 没有 None
B. 双音固定(f1 > f2) Fixed setting two tones (f1 > f2)
C. 低音f1 扫描(定量f2 > 变量f1) Sweeping the Bass tone f1 (fixed f2 > variable f1)
D. 语音f2扫描(定量f1 < 变量f2) Sweeping the voice tone f2 (fixed f1 < variable f2)
E. 以恒定频率比率f2/f1=const 扫描双音 Sweeping two tone sweep with
constant frequency ratio f2/f1=const
F. 其他 Other
KLIPPEL LIVE #9: Intermodulation Distortion, 14
Setup for IMD in Sound Pressure bass sweep technique
最佳激励 Optimal Stimulus:
双音激励 Two-Tone stimulus
低音频率在共振附近变化 0.5fs < f1 < 2fs Varying frequency of bass tone about resonance 0.5fs < f1 < 2fs
高于共振的恒定语音频率f2 =7fs Constant frequency of voice tone above resonance f2 =7fs
要求 Requirement:
两个正弦发生器、频谱分析仪 2 sinusoidal generators, Spectrum analyzer
Bass tone f1
Loudspeaker~
FT
Microphone Spectrum
Analyzer
Amplifier
~voice tone f
2
Amplitude response
versus frequency f1 :
2nd-order IMD
3rd –order IMD
frequency
KLIPPEL LIVE #9: Intermodulation Distortion, 15
Causes of IMD in Sound Pressure Output using bass sweep technique
Cone Vibration
L(i)
Bl(x)
L(x)
Doppler Effect
L(i)
Bl(x)
L(x)
L(i)
Cone Vibration
Doppler
IMD%
fs
30
f1bass tone
voice tone
f2=10fsdistortion is
minimal
above fs
IMD generated by voice
displacement
Kms(x) negligible
IMD generated by current
KLIPPEL LIVE #9: Intermodulation Distortion, 16
Demo: Intermodulation Distortion2 tone stimulus with bass sweep
Tools of the KLIPPEL Analyzer:
• 3D Distortion Measurement (DIS)
KLIPPEL LIVE #9: Intermodulation Distortion, 17
Measurement of IMD in Sound Pressure voice sweep technique
最佳激励 Optimal Stimulus:
双音激励 Two-Tone stimulus
语音频率高于共振处变化5fs < f2 < 20fs Varying frequency of voice tone above resonance 5fs < f2 < 20fs
低于共振的恒定低音频率f1 < 0.5fs Constant frequency of bass tone below resonance f1 < 0.5fs
要求 Requirement:
ALMA测试CD、双音发生器、频谱分析仪、麦克风 ALMA Test CD, 2 tone generators, Spectrum
analyzer, Microphone
Bass tone f1
Loudspeaker~
FT
Microphone Spectrum
Analyzer
Amplifier
~voice tone f
2
Amplitude response
versus frequency f1 :
2nd-order IMD
3rd –order IMD
frequency
KLIPPEL LIVE #9: Intermodulation Distortion, 18
The Causes of IMD in Sound Pressure Outputvoice sweep technique
Cone Vibration (at maxima of AAL)
L(i) (rising with f2 )
Bl(x) independent of f2
L(x) (rising with f2 )
Doppler Effect (rising with f2 )
Bl(x)
L(x)
L(i)
Cone Vibration
Doppler
IMD
%
f 220f s7f s
20 -
variable voice tone
fixed
bass tone
f2=0.5fs
independent of frequency
distinct frequencies
L(x) ,L(i) and Doppler
Bl(x)
Cone Vibration
Kms(x) negligible
KLIPPEL LIVE #9: Intermodulation Distortion, 19
Demo: Intermodulation Distortion2 tone stimulus with voice sweep
Tools of the KLIPPEL Analyzer:
• 3D Distortion Measurement (DIS)
KLIPPEL LIVE #9: Intermodulation Distortion, 20
Sparse but Comprehensive Stimulus
Stimuli
Single-
Tone
Two-
Tone
Multi-
ToneNoise Audio
Signal
complexity
Spectral Analysis
Time Domain
AnalysisEnvelope
Calculation
Phase
Modulation
Amplitude
Modulation
Total Distortion
2nd-order
3rd-order
Amplitude Phase
Intermodulation Distortion
Harmonics of the two tones
KLIPPEL LIVE #9: Intermodulation Distortion, 21
Amplitude Modulationtwo-tone stimulus f1 < fs, f2 > fs
-5,0
-2,5
0,0
2,5
5,0
0,05 0,10 0,15 0,20 0,25 0,30
Sound pressure Pfar(t) in far fie ld vs tim e
Pfar
[ N
/ m^
2 ]
T im e [s ]
P far(t)
Symmetrical
Force factor
Bl(x)
Cycle
peak
Rest positionKLIPPEL
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0
4,5
5,0
-5 -4 -3 -2 -1 0 1 2 3 4 5
Bl(x)[N/A]
[mm] x BottomMean
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-10,0
-7,5
-5,0
-2,5
0,0
2,5
5,0
7,5
10,0
0,08 0,09 0,10 0,11 0,12 0,13 0,14
Sound pressure Pfar(t) in far fie ld vs tim e
Pfar
[ N
/ m^
2 ]
T im e [s ]
wi thout Doppler wi th Doppler
Phase (Frequency) Modulationcaused by Doppler Effect
-7,5
-5,0
-2,5
0,0
2,5
5,0
7,5
10,0
0,106 0,107 0,108 0,109 0,110 0,111 0,112 0,113
Sound pressure Pfar(t) in far fie ld vs tim e
Pfar
[ N
/ m^
2 ]
T im e [s ]
wi thout Doppler wi th Doppler
Phase variation
KLIPPEL LIVE #9: Intermodulation Distortion, 23
Phase of Intermodulation Distortion
Amplitude ModulationFrequency Modulation
(Phase Modulation)
variation
of envelope
12 ff − 12 ff +
phase
variation
1f 2f
L
amplitude
spectrum
2f
in-phase
12 ff −12 ff +
90 degree phase shift
2f
12 ff −
12 ff +
KLIPPEL LIVE #9: Intermodulation Distortion, 24
互调失真的可听度Audibility of Intermodulation Distortion
关键条件 Critical condition:• 低音调制频率要足够低(fB < 30 Hz) modulation frequency of the „bass tone“ is sufficiently low (fB < 30 Hz)
• 语音载波频率在1kHz (80 dB SPL) Carrier frequency of the voice tone is at 1 kHz tone (80 dB SPL)
简短总结 Short summary
→ AM调制(例如力因数失真)在3%时可闻并被感知为粗糙度AM modulation (e.g. force factor distortion) are audible at 3 % and perceived as roughness
→ FM调制的阈值在30%变得可闻 Threshold of FM modulation become audible at 30 %
→ 多普勒失真不重要 Doppler distortion are not critical
Zwicker, Fastl, 1999
更多内容在第14期:为信号失真设置有意义的公差(8月12日)More in section #14: Setting meaningful tolerances for Signal Distortion (August 12th)
KLIPPEL LIVE #9: Intermodulation Distortion, 26
IM-Distortion (two-tone signal)Definitions according IEC 60268-21
Second-order Modulation
(FM + AM)
2 1 2 12
2
( ) ( )20 lg
( )IMD
p f f p f fL
p f
− + +=
Third-order Modulation
(FM + AM)
2 1 2 13
2
( 2 ) ( 2 )20 lg
( )IMD
p f f p f fL
p f
− + +=
Total Modulation Distortion
(FM+ AM)
2
2 1 2 1
1
1 2
2
( ) ( )
( , ) 20 lg( )
k
TIMD
p f kf p f kf
L f fp f
=
− + +
=
Amplitude Modulation
(AM only)
=
=K
k
kEK
E1
][1
( )%100*
][2
1
2
E
EkEK
d
K
k
AMD
=
−
=
=
100lg20 AMD
AMD
dL
KLIPPEL LIVE #9: Intermodulation Distortion, 27
Interpretation of the Envelope
KLIPPEL
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2
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Amplitude modulation distortion
(AMD)
dB
Frequency f1 [Hz]
M top M bottom Mean Value Limits
Cone Boundary Condition
(mode of the surround)
Force factor
Cone geometry
KLIPPEL LIVE #9: Intermodulation Distortion, 28
幅度调制在总互调失真中的贡献Contribution of Amplitude Modulation
to the total intermodulation distortion
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Modulation distortion (U1=1 V)
dB
Frequency f1 [Hz]
AM distortion (Lamd) Ldm (cumul)
Total modulation
AM modulation(force factor, inductance, cone vibration)
Doppler
KLIPPEL LIVE #9: Intermodulation Distortion, 29
Demo: Amplitude Modulation2 tone stimulus with voice sweep
Tools of the KLIPPEL Analyzer:
• 3D Distortion Measurement (DIS)
KLIPPEL LIVE #9: Intermodulation Distortion, 30
Intermodulation Measurement
using a Two-Tone Stimulus
缺点 Disadvantages:
• 激励音频率需要小心设置 Frequency of excitation tones have to be set carefully
优点 Advantages:
• 易于生成(使用两个正弦发生器)Simple generation (by using two sinusoidal generators)
• 分离噪声和失真 Separation of noise and distortion
• 易于解读 Easy to interpret
• 适于研发中的扬声器诊断 Good for loudspeaker diagnostics in R&D
• 灵敏激励也适用于听音测试 Sensitive stimulus also for listening tests
KLIPPEL LIVE #9: Intermodulation Distortion, 31
Universal Stimuluscomplex, steady-state, like an organ tone
Single-
Tone
Two-
Tone
Multi-
ToneNoise Audio
Signal
Spectral Analysis
complexity of the stimulus
sparse excitation
Amplitude and Phase response
Fundamental Components Multi-tone Distortion(harmonics, intermodulation)
some frequencies are not excited !!!
KLIPPEL LIVE #9: Intermodulation Distortion, 32
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Spectrum p(f) of microphone signal
[dB
]Frequency [Hz]
Signal lines Noise + Distortions Noise floor
Signal level MTND
Multi-Tone Distortion (MTD)
→MTD没有详细显示生成过程MTD don‘t show the generation process in detail
→ “指纹”特性(适用于质控)„Fingerprint“ (good for quality control)
• 基波频率处的失真 distortion at fundamental frequencies
• 谐波分量 harmonic components
• 差频分量 difference-tone components
• 和频分量 summed tone components
互调 intermodulation
Distortionf
Sparse multi-tone complex
Stimulus Output signal
KLIPPEL LIVE #9: Intermodulation Distortion, 33
Poll:您是否评估多音激励产生的失真?Do you evaluate the distortion generated by a multi-tone stimulus ?
A. Yes
B. No
KLIPPEL LIVE #9: Intermodulation Distortion, 34
激励音的相位很重要!Phase of the Excitation Tones is important !!
KLIPPEL
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Stimulus (t) vs time
[V]
Time [ms]
Stimulus (t)
Time signal (logarithmic sweep)
f
Phase spectrum
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dB - [V]
(rms)
Frequenc y [Hz]
Curve 2
Amplitude spectrum
任何时候都有多个频率分量相互作用!At any time there are multiple frequency components
interacting !!!
互调+谐波 Intermodulation + Harmonics
一次只有一个频率分量!At one time there is only one frequency component !!!
只有谐波 Harmonics only
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Time Signal (Multi-tone complex)
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Phase spectrumKLIPPEL
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[dB] 0 dB =
1 V
Frequency [Hz]
Amplitude spectrum
random
KLIPPEL LIVE #9: Intermodulation Distortion, 35
符合IEC60268-21多音激励的定义属性Defined Properties of Multi-tone Stimulus
according IEC 60268-21
目标 Objective:
- 确保不同仪器测量结果的可比性 ensure comparability of the results measured by different instruments
- 易于生成(通过软件实现)easy to generate (by software implementation)
- 激励的修改是可行的(带宽、分辨率R)Modification of the stimulus should be possible (bandwidth ,
resolution R)
( ) NiwithfTT
fRi
starti ,...,12int1 /
==
=+ m
i
i
ma
mmod
2
*21
( ) ( )=
+=N
i
iii tffUtx1
2cos)(
Frequencies of the sparse line spectrum logarithmically spaced Pseudo-random phase
Amplitude spectrum
Max. Number of
frequencies Seeds (a=48271, m=231-1 and 1=1) Starting
frequencyDuration
(periodicity)
resolution
KLIPPEL LIVE #9: Intermodulation Distortion, 36
Interpretation of the Distortion
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[dB]
Frequency [Hz]
Fundamental Multi -tone Distortion
Distortion
Fundamental
frequency of the spectral components
Total Harmonic Distortion (THD) Multi-tone Distortion
Sound pressure spectrum
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50 100 200 500 1k 2k 5k
dB - [V] (rm
s)
Frequency [Hz]
Fundamental THD
Total Harmonic Distortion (THD)
FundamentalFundamental
frequency of the fundamental tone
THD
好处:基波和失真之间的距离对于感知掩盖效应很有意义 Benefit: Distance between fundamentals
and distortions is meaningful for perceptual masking
KLIPPEL LIVE #9: Intermodulation Distortion, 37
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[dB]
Frequency [Hz]
MTND THD IMD
Multi-tone Distortion Measurement
compared with traditional THD, IMD
MTD
IMD:
f1 = 50 Hz @15 V
+ sweep @ 3V
MTD:
Multitone @ 15V
THD:
sweep @ 15 V
600 Hz40 Hz 600 Hz
THD0.1 %
IMD10 %
1 %
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The Causes of Multi-Tone DistortionKLIPPEL
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[dB]
Frequency [Hz]
Fundamental Multi -tone Distortion
Distortion
Fundamental
resonance frequency Cone Vibration
L(i) (rising with frequency)
Bl(x) (independent of frequency)
Kms(x)
L(x) (rising with frequency)
Doppler (rising with frequency)
Kms(x)
Bl(x)
L(x)
L(i)
Cone Vibration
Doppler Effect
Rms(v)Rms(v)
frequency of the spectral component
KLIPPEL LIVE #9: Intermodulation Distortion, 39
Exercise: WooferAnalysis of Multi-tone Distortion
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Spectrum sound pressure output
[dB
]
Frequency [Hz]
fundamental components
Bl(x)Kms(x)
Le(x)
Rms(v) Le(i)Bl(x)Kms(x)Le(x) Doppler Effect Cone Vibrationcauses:
total distortion
fs=60 Hz
out of band distortion
Le(i)
KLIPPEL LIVE #9: Intermodulation Distortion, 40
Exercise: MicrospeakerAnalysis of Multi-tone Distortion
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Distortion Components
[ dB
]
Le(i)
fundamental components
20
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Frequency [Hz]
Bl(x)
Kms(x)
Le(x)
Rms(v) Le(i)Bl(x)Kms(x)Le(x) Doppler Effect Cone Vibrationcauses:
out of band distortion
total distortion
Rms(v)
fs=600 Hz
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多音失真的测量Measurement of Multi-Tone Distortion
缺点 Disadvantages:
• 激励的幅值和相位必须由标准定义 Amplitude and phase of stimulus have to be defined by standard
• 奇次和偶次失真分量不能分离 no separation of odd- and even-order distortion components
• 不能揭示非线性的非对称性 does not reveal the asymmetry of the nonlinearities
• 谐波和互调不能分离 no separation of harmonics and intermodulation
• 基波分量也失真了 fundamental components are also distorted
优点 Advantages:
• 考虑了互调分量 Considers intermodulation components
• 类音频信号 Audio-like signal
• 分离噪声和失真 Separation of noise and distortion
• 快速(非常适合质控)fast (perfect for quality control)
此测量在扬声器诊断中非常强大!This measurement is very powerful in loudspeaker diagnostics !
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Demo. Multi-tone Distortion
Tool: Using a dedicated software module MTON (multi-tone) of the
KLIPPEL Analyzer
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Discussion
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Summary
• 互调失真可提供谐波无法提供的有价值的诊断信息IM-Distortion give valuable diagnostic information not provided by harmonics
• 互调失真是L(x) 非线性的唯一症状(通过短路环减少)IM-Distortion is the only symptom for L(x) nonlinearity (reduced by shorting rings)
• 多音测量提供了所有非线性失真分量的全面指纹信息Multi-tone measurements gives a comprehensive fingerprint of all nonlinear distortion components
• 多音测试显示程序材料的影响Multi-tone testing shows the impact of the program material
• 双音激励提供更多详细信息,是听音的最关键信号Two-tone stimulus gives more detailed information and is the most critical signal for listening
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Open Questions
如何评估音频设备的非常规性能?How to evaluate the irregular properties of the audio device ?
第10期网络研讨会主题 The next 10th KLIPPEL live webinar entitled
脉冲失真 – 异音、异常行为、缺陷Impulsive distortion - rub&buzz, abnormal behavior, defects
将讨论 will address the points:
• 需要比人耳更灵敏的特殊测量Need for special measurements more sensitive than the human ear
• 时频分析能展示什么 What the Time-Frequency analysis shows
• 在时域调查脉冲失真的精细结构Inspecting the fine-structure of impulsive distortion in the time domain
• 如何找出非常规行为的根本原因 How to find the root cause of the irregular behavior
• IEC 60268-21提供的新解决方案 New solutions provided by IEC 60268-21
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1. Modern audio equipment needs output based testing
2. Standard acoustical tests performed in normal rooms
3. Drawing meaningful conclusions from 3D output measurement
4. Simulated standard condition at a single evaluation point
5. Maximum SPL – giving this value meaning
6. Selecting measurements with high diagnostic value
7. Amplitude Compression – less output at higher amplitudes
8. Harmonic Distortion Measurements – best practice
9. Intermodulation Distortion – music is more than a single tone
10. Impulsive distortion - rub&buzz, abnormal behavior, defects
-- small break --
11.Smart speaker testing with wireless audio input (July 22nd)
12.Benchmarking of audio products under standard conditions
13.Auralization of signal distortion – perceptual evaluation
14.Setting meaningful tolerances for signal distortion
15.Rating the maximum SPL value for product
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