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Natural Test Signal

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NATURAL TEST SIGNAL
Theory and measurements
В© Kalervo Kuikka
1
NATURAL TEST SIGNAL
В© K.Kuikka 2007
In general
Natural test signal is designed for quality measurements of audio frequency
devices. It is wideband synchronous multi-tone test signal, which frequencyand power distribution equals to common music.
Natural test signal is periodic test signal, in which all signal components
are mathematically well-defined (frequency, phase and amplitude) and they
are fixed proportional to the fundamental frequency. For these reasons it is
possible to measure coarse response errors by using an oscilloscope that is
trigged to the fundamental frequency. Carrying out high-performance
response error measurements spectrum analyser is needed.
Natural test signal is mathematically very simple => It is easy to analyse
measurement results.
2
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Generating Natural Test Signal
Generating Natural Test Signal is extremely simple.
Mother Signal of Natural Test Signal can be produced by
summing ideal fundamental frequency square wave and inverted
phase pure fundamental frequency sine wave at such a level that
fundamental frequency component of summing signal will be
completely disappeared.
Mother Signal can also be produced by ideal band stop filter
(tuned to fundamental frequency). If ideal square wave goes
through band stop filter fundamental frequency component of
square wave is completely disappeared.
3
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Generating Natural Test Signal
пѓ™
Square wave, which DC component is 0 and peak value
as follows :
пѓ™
U (t ) пЂЅ U
U
, can be described
4 пѓ¦
1
1
1
1
пѓ¶
sin 7 пЃ· t пЂ« . . .пЂ«
sin n пЃ· t пѓ·
пѓ§ sin пЃ· t пЂ« sin 3пЃ· t пЂ« sin 5пЃ· t пЂ«
пѓё
пЃ° пѓЁ
3
5
7
n
and fundamental frequency sine wave can be described :
пѓ™
U ( t ) пЂЅ U sin пЃ· t
When summing square wave and phase inverted fundamental frequency sine
wave component :
пѓ™
пЂ­U
4
пЃ°
sin пЃ· t
, we get as a result Natural Test Signal :
пѓ™
4пѓ¦
1
1
1
1
пѓ¶ пѓ™ 4
U ( t ) пЂЅ U пѓ§ sin пЃ· t пЂ« sin 3пЃ· t пЂ« sin 5пЃ· t пЂ« sin 7 пЃ· t пЂ« ...пЂ« sin n пЃ· t пѓ· пЂ­ U
sin пЃ· t пЂЅ
пѓё
пЃ° пѓЁ
3
5
7
n
пЃ°
пѓ™
U
4пѓ¦ 1
1
1
1
пѓ¶
пѓ§ sin 3пЃ· t пЂ« sin 5пЃ· t пЂ« sin 7 пЃ· t пЂ« ...пЂ« sin n пЃ· t пѓ·
пѓё
пЃ° пѓЁ 3
5
7
n
4
Generating Natural Test Signal
NATURAL TEST SIGNAL
В© K.Kuikka 2007
When summing to square wave (275 Hz , uppermost
picture ) in phase inverted …
distortion free pure sine wave ( picture in the middle)
in such a level that fundamental frequency
component of square wave is fully got off then we
get as a result …
Natural Test Signal (undermost picture) , which is
very effective signal on testing all audio devices. In
the picture there is Mother Signal only.
5
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Choosing funtamental frequency
Fundamental frequency of Natural Test Signal can be chosen freely. In this case
fundamental frequency has been chosen such a way that spectrum of square
wave equals common music signal. To avoid noise caused by power supplies of
testing devices fundamental frequency is not allowed to be harmonic of mains
frequency ( 50 / 60 Hz). Because of these arguments fundamental frequency is
chosen 275 Hz in this application.
Fundamental frequency ( 275 Hz) described in this application is suitable for
testing purposes of all audio devices in middle and high frequency region. If we
must carry out tests in bass region we ought to choose lower fundamental
frequency ( 20 – 30 Hz).
6
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Mother and Daughter Signals
Allthough the Mother Signal itself is a very efficient test signal
the character of Natural Test Singnal can still be improved by
summing into it daughter signals with higher frequency than
fundamental.
In summing daughter signals and Mother Signal we must keep in
mind that the peak value of Natural Test Signal does not become
too high. The summing principle is that amplitude of
daughtersignals is 0 when mother signal is at its peak value.
7
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Mother and Daughter Signals
Daughter Signals phase locked to fundamental can be generated
by modulating the sine wave carrier (sin пЃ· m t , m>4 , phase
locked to fundamental ) with the fundamental sine wave
( sin пЃ· t ). In this case we get two Daughter Signals as follows:
sin m пЃ· t пѓ— sin пЃ· t пЂЅ
1
2
cos пЂЁ m пЂ­ 1пЂ© пЃ· t пЂ­
1
2
cos пЂЁ m пЂ« 1пЂ© пЃ· t
We can see that Daughter Signals are amount of fundamental
frequency above and beneath the carrier frequency.
8
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Mother and Daughter Signals
Daughter Signals can also be generated by using a square wave as a carrier
and then we get more daughter signals than two.
In this case carrier is :
and modulating signal:
1
1
1
пѓ¦
пѓ¶
sin nm пЃ· t пѓ·
пѓ§ sin m пЃ· t пЂ« sin 3 m пЃ· t пЂ« sin 5 m пЃ· t пЂ« ... пЂ«
пѓЁ
пѓё
3
5
n
sin пЃ· t
Daughter Signals are generated as follows:
1
1
1
пѓ¦
sin
m
пЃ·
t
пЂ«
sin
3
m
пЃ·
t
пЂ«
sin
5
m
пЃ·
t
пЂ«
...
пЂ«
sin nm пЃ·
пѓ§
пѓЁ
3
5
n
пѓ¶
t пѓ· пѓ— sin пЃ· t пЂЅ
пѓё
1
1пѓ¦1
1
пѓ¦1
пѓ¶
пѓ¶
пѓ§ cos пЂЁ m пЂ­ 1пЂ©пЃ· t пЂ­ cos пЂЁ m пЂ« 1пЂ©пЃ· t пѓ· пЂ« пѓ§ cos пЂЁ 3 m пЂ­ 1пЂ©пЃ· t пЂ­ cos пЂЁ 3 m пЂ« 1пЂ©пЃ· t пѓ· пЂ«
пѓЁ2
пѓё
пѓё
2
3 пѓЁ2
2
1пѓ¦1
1
1 пѓ¦1
1
пѓ¶
пѓ¶
пѓ§ cos пЂЁ 5 m пЂ­ 1пЂ©пЃ· t пЂ­ cos пЂЁ 5 m пЂ« 1пЂ©пЃ· t пѓ· пЂ« ... пЂ« пѓ§ cos пЂЁ nm пЂ­ 1пЂ©пЃ· t пЂ­ cos пЂЁ nm пЂ« 1пЂ©пЃ· t пѓ·
пѓё
пѓё
5 пѓЁ2
2
n пѓЁ2
2
9
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Mother and Daughter Signals
Using square wave as a carrier on generating Daughter Signals
is very advantageous when it makes band with on Natural Test
Signal higher. Test signal is then more effective to bring
forward group delay errors on higher frequencies.
The sum of Daughter Signals is at any time 0 when Mother
Signal is at its peak value, because (sin пЃ·t ) = 0 at this point .
Summing Daughter Signals into Mother Signal does not
increase the peak value of Natural Test Signal at the peaks of
pure Mother Signal.
On summing Daughter Signals into Mother Signal it is possible
to increase signal power at desired measuring range and at the
same time crest factor of Natural Test Signal becomes lower.
10
Mother and Daughter Signals
NATURAL TEST SIGNAL
В© K.Kuikka 2007
We can generate Mother Signal (uppermost picture)
of Natural Test Signal when we fully remove
fundamental frequency component of ideal square
wave. Pure Mother Signal has crest factor only 2.3
In picture in the middle we can see Daughter Signals
made by modulating process. In this case carrier
wave is square wave phase locked to fundamental
frequency.
When summing Daughter Signals into Mother Signal
(undermost picture) we can increase signal power at
“valleys” of pure Mother Signal. When we adjust the
level of Daughter Signals so that summing signal
reaches peak value of Mother Signal, crest factor
decreases to value 1.51.
11
NATURAL TEST SIGNAL
В© K.Kuikka 2007
”Wild” Daughter Signals
If a carrier wave we use generating Daughter Signals is not
phase locked to fundamental frequency, Daughter Signals
obtain “wild” behaviour on scope trigged to fundamental
frequency. On scope screen we can see very interesting figures,
which are very strange for sine wave orientated men. On doing
some measurements “wild” Daughter Signals are very effective
to detect response errors.
12
”Wild” Daughter Signals
Fig 1
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Fig 1 Mother Signal only
Fig 2 Mother Signal an low level Daughter
Signals
Fig 3 The level of Daughter Dignals are
adjusted to the peak level of Mother Signal
Fig 2
Fig 4 The level of Daughter Signals are
ajdusted above peak level of Mother Signal.
Scope wievs at generator output. Under tests
Scope was trigged to fundamental frequency.
Fig 3
Fig 4
13
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Sweeping Daughter Signals
The carrier wave we use on generating Daughter Signals is not
necessary to be phase locked to fundamental frequency. That
is why we can use also sweep signal as a carrier wave. In this
case we get two sweeping Daughter Signals, which have
frequency difference of two times fundamental frequency all
the time in spite of sweeping frequency.
Without risk of overdrive testing device we can drive it full
dynamic range with Mother Signal and simultaneously also
drive with sweeping Daughter Signals. Second order inter
modulation product of Daughter Signals can be measured on
frequency of two times fundamental frequency all the time
during sweeping section.
14
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Superior features
Natural Test Signal has many superior features compared to
other multi-tone test signals.
Spectrum and power distribution of the signal equals to common
music signal and signal is distinctly periodic. This feature makes
very easy to see coarse wide band response errors with an
oscilloscope, which is trigged to the fundamental frequency.
There are free space for inter modulation products on
fundamental frequency and two times fundamental. Second order
inter modulation products generated to higher frequencies are
directed between odd harmonics of Natural Test Signal.
15
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Superior features
Using Daughter Signals there is very easy to increase signal
power at higher frequencies where power of Mother Signal is
quite low.
Carrier we use in generating Daughter Signals must not be phase
locked to the fundamental frequency thus we can use also sweep
signal as a carrier.
Natural Test Signal is very sensitive signal form to detect group
delay errors of a test device. Signal distorts very sensitively if
group delay errors occur.
Generating Natural Test Signal is very easy.
16
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Scope wiev of sine wave
Fundamental frequency = 275 Hz
Spectrum of sine wave ( f = 275 Hz)
Span = 6.4 KHz
Y = 10 dB/div
17
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Average spectrum of a music signal.
Average result of 200 measurements.
Span = 12.8 KHz
Y = 10 dB/div
Spectrum of Natural Test signal
(fundamental frequency = 275 Hz)
Fundamental frequency component has
been fully removed thus lowest
frequency component of Natural Test
Signal is 3*275 =825 Hz
Span = 12.8 KHz
Y = 10 dB/div
18
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Average spectrum of a music signal.
Average result of 200 measurements.
Span = 12.8 KHz
Y = 10 dB/div
Scope wiev of a coincidental music
signal
19
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Spectrum of Natural Test Signal
( Mother Signal only )
Span = 12.8 KHz
Y = 10 dB/div
Scope wiev of Natural Test Signal
( Mother Signal only )
Rise time (adjustable ) of the signal is
5.3 пЃ­s in this picture.
20
NATURAL TEST SIGNAL
В© K.Kuikka 2007
14*275Hz square wave carrier modulated
by fundamental frequency sine wave
generates Daughter Signals on frequencies
(14*275 – 275) Hz and (14*275 + 275) Hz.
In the picture we can see also Daughter
Signals on frequencies (3*14*275 –275) Hz
and (3*14*275 + 275) Hz.
Daughter Signals are marked by blue arrows.
Span = 12.8 KHz
Y = 10 dB/div
Scope wiev of Natural Test Signal (mother
signal + daughter signals).
Natural Test Signal signal seems to be quite
similar character as a music signal but it is
not fully coincidental. It is distincly periodic
signal.
21
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Scope wiev of a coincidental music
signal
Scope wiev of Natural Test Signal
(Mother Signal + Daughter Signals).
Natural Test Signal signal seems to be
quite similar character as a music signal
but it is not fully coincidental. It is
distincly periodic signal.
22
Mearuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
We examined the behaviour of Natural Test signal in non linear
device with a testing device specially designed on this purpose.
Testing device could be adjusted to bring out different types of
distortions.
At first we adjusted the distortion of the testing device to 1%
using pure sine wave (275 Hz). After that we changed sine
wave to Natural Test Signal (Mother Signal and different kinds
of Daughter Signals) having same amplitude and carried out
distortion measurements. We took screenshots from scope and
spectrum analyser in each measurements.
In the pictures distortion products have been marked with red
arrows and Daughter Signals with blue arrows.
23
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
In distortion measurement pictures testing signals have been presented
as follows:
sine275
275 Hz fundamental frequency sine wave
natural
Mother Signal of Natural Test Signal
natural_13_15
Natural Test Signal including Daughter Signals at
frequencies 13 and 15 times fundamental frequency
natural_14_16
Natural Test Signal including Daughter Signals at
frequencies 14 and 16 times fundamental frequency
24
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Quadradic distortion 1 %
Signal: Sine275
At the scope screen we cannot notice any
distortion
We can see that second harmonic (550
Hz) is over 20 dB stronger than third
harmonic (825 Hz)
Span = 6.4 KHz
Y = 10 dB/div
25
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Quadradic distortion 1%
Signal: Natural
At the scope screen we cannot notice any
distortion
Fundamental frequency distortion
component is quite low but even
harmonics components (550 , 1100, 1650
Hz…) are much higher
Span = 6.4 KHz
Y = 10 dB/div
26
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Quadradic distortion 1%
Signal: Natural_13_15
At the scope screen we cannot notice any
distortion
Around Daughter Signals there are
generated quite high level distortion
components
Span = 6.4 KHz
Y = 10 dB/div
27
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Quadradic distortion 1%
Signal: Natural_14_16
At the scope screen we cannot notice
any distortion
Highest distortion component is at the
frequency of 1100 Hz
Span = 6.4 KHz
Y = 10 dB/div
28
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Clipping distortion 1%
( positive / negative peaks )
Signal: Sine275
At the scope screen clipping both
positive and negative peaks is very
clearly seen.
Spectrum shows that odd harmonics are
stronger than even harmonics.
Span = 6.4 KHz
Y = 10 dB/div
29
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Clipping distortion 1%
( positive / negative peaks )
Signal: Natural
At the scope screen clipping both
positive and negative peaks is very
clearly seen.
Spectrum shows that clipping generates
very many low level distortion
components. Strongest distortion
component is at fundamental frequency
(275 Hz).
Span = 6.4 KHz
Y = 10 dB/div
30
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Clipping distortion 1%
( positive / negative peaks )
Signal: Natural_13_15
At the scope screen clipping both
positive and negative peaks is very
clearly seen.
Strongest distortion component is at
fundamental frequency (275 Hz).
Span = 6.4 KHz Y = 10 dB/div
31
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Clipping distortion 1%
( positive / negative peaks )
Signal: Natural_14_16
At the scope screen clipping both
positive and negative peaks is very
clearly seen.
Clipping generates many distortion
components. Strongest distortion
component is at the frequency of two
times fundamental frequency (550 Hz).
Span = 6.4 KHz Y = 10 dB/div
32
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Clipping distortion 1%
( negative peaks only )
Signal: Sine275
At the scope screen clipping negative
peaks is very clearly seen.
Clipping generates a great amount of
even and odd distortion components.
Span = 6.4 KHz Y = 10 dB/div
33
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Clipping distortion 1%
( negative peaks only )
Signal: Natural
At the scope screen clipping negative
peaks is very clearly seen.
In spectrum view we can see distortion
products to spread to wide bandwidth
Span = 6.4 KHz Y = 10 dB/div
34
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Clipping distortion 1%
( negative peaks only )
Signal: Natural_13_15
At the scope screen clipping negative
peaks is very clearly seen.
In spectrum view we can see that
summing Daughter Signals into Mother
Signal increases distortion products
clearly.
Span = 6.4 KHz Y = 10 dB/div
35
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Clipping distortion 1%
( negative peaks only )
Signal: Natural_14_16
At the scope screen clipping negative
peaks is very clearly seen.
In spectrum view we can see high
distortion products to spread to wide
bandwidth.
Span = 6.4 KHz
Y = 10 dB/div
36
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Cross over distortion 1%
Signal: Sine275
At the scope screen cross over distortion
of sine wave is just observable.
In spectrum view we can see that odd
harmonics are higher than even
harmonics.
Span = 6.4 KHz Y = 10dB/div
37
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Cross over distortion 1%
Signal: Natural
At the scope screen cross over distortion
is not observable.
In spectrum view we can see that highest
distortion component has been generated
to the fundamental frequency (275 Hz).
Span = 6.4 KHz Y = 10 dB/div
38
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Cross over distortion 1%
Signal: Natural_13_15
At the scope screen cross over distortion
is not observable.
In spectrum view we can see that highest
distortion component has been generated
to the fundamental frequency (275 Hz).
Span = 6.4 KHz Y = 10 dB/div
39
Measuring distortion
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Cross over distortion 1%
Signal: Natural_14_16
At the scope screen cross over distortion
is not observable.
In spectrum view we can see that highest
distortion component has been generated
to the fundamental frequency (275 Hz).
Span = 6.4 KHz Y = 10 dB/div
40
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Natural Test Signal in digital recording and MP3 compressing
Tests were carried out by recording test signals sine275, natural
and natural_13_15 at sampling frequency 44.1 KHz and saving
recordings to the hard disk of the computer as uncompressed WAV
files. WAV audio files were then compressed 192 Kbps, 128 Kbps
and 96 Kbps MP3 files and they also were saved to the hard disk.
When playing all recorded audio files we measured response errors
of Natural Test Signal in digital recording and MP3 compressing.
Testing point was output of audio card of the computer.
41
Digital recording and
MP3 compressing
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Uncompressed WAV file. Sampling
frequency is 44.1 KHz .
Signal: Sine275
Fundamental frequency sine wave is
error free.
Spectrum of sine wave is as clean as at
the output of signal generator
Span = 6.4 KHz Y = 10 dB/div
42
Digital recording and
MP3 compressing
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Uncompressed WAV file. Sampling
frequency is 44.1 KHz
Signal: Natural
Mother Signal is error free. Due to
limited sampling frequency some peaks
have been formed.
Spectrum of Mother Signal is as clean as
at the output of signal generator. Digital
recording causes no dirtortion.
Span = 6.4 KHz Y = 10 dB/div
43
Digital recording and
MP3 compressing
NATURAL TEST SIGNAL
В© K.Kuikka 2007
Uncompressed WAV file. Sampling
frequency is 44.1 KHz .
Signal: Natural_13_15
Due to limited bandwidth Natural Test
signal has been formed spiky but other
response errors does not occur.
Spectrum of Natural Test Signal is error
free.
Span = 6.4 KHz Y = 10 dB/div
44
Digital recording and
MP3 compressing
NATURAL TEST SIGNAL
В© K.Kuikka 2007
To bit rate 192 Kbps converted MP3 file.
Signal: Sine275
Compression does not cause any response
errors to sine wave.
Spectrum of fundamental frequency sine
wave is distortion free.
Span = 6.4 KHz Y = 10 dB/div
45
Digital recording and
MP3 compressing
NATURAL TEST SIGNAL
В© K.Kuikka 2007
To bit rate 192 Kbps converted MP3 file
Signal: Natural
At the scope screen Mother Signal has
become a little bit noisy.
Spectrum of Mother Signal has become
quite noisy. In the picture there is average
test result of 30 measurements.
Span = 6.4 KHz Y = 10 dB/div
46
Digital recording and
MP3 compressing
NATURAL TEST SIGNAL
В© K.Kuikka 2007
To bit rate 192 Kbps converted MP3 file
Signal: Natural_13_15
Natural Test Signal has become quite
noisy.
Spectrum of Natural Test Signal has
become quite noisy. In the picture there is
average test result of 30 measurements.
Span = 6.4 KHz Y = 10 dB/div
47
Digital recording and
MP3 compressing
NATURAL TEST SIGNAL
В© K.Kuikka 2007
To bit rate 128 Kbps converted MP3 file.
Signal: Sine275
Compression has not caused any response
errors to fundamental frequency sine
wave.
Compression has not caused any errors to
the spectrum view.
Span = 6.4 KHz
Y = 10 dB/div
48
Digital recording and
MP3 compressing
NATURAL TEST SIGNAL
В© K.Kuikka 2007
To bit rate 128 Kbps converted MP3 file
Signal: Natural
Mother Signal has become very noisy at
the scope screen.
Spectrum of Mother Signal has become
very noisy. In the picture there is average
test result of 30 measurements.
Span = 6.4 KHz Y = 10 dB/div
49
Digital recording and
MP3 compressing
NATURAL TEST SIGNAL
В© K.Kuikka 2007
To bit rate 128 Kbps converted MP3 file
Signal: Natural_13_15
Natural Test Signal has become very
noisy at the scope screen.
Spectrum of Natural Test Signal has
become very noisy. In the picture there is
average test result of 30 measurements.
Span = 6.4 KHz Y = 10 dB/div
50
Digital recording and
MP3 compressing
NATURAL TEST SIGNAL
В© K.Kuikka 2007
To bit rate 96 Kbps converted MP3 file
Signal: Sine275
At the scope screen fundamental
frequency sine wave is error free.
A little bit noise has been produced near
the fundamental frequency. In the picture
there is average test result of 30
measurements.
Span = 6.4 KHz Y = 10 dB/div
51
Digital recording and
MP3 compressing
NATURAL TEST SIGNAL
В© K.Kuikka 2007
To bit rate 96 Kbps converted MP3 file
Signal: Natural
At the scope screen Mother Signal is
extremely noisy.
Spectrum of Mother Signal has become
extremely noisy. In the picture there is
average test result of 30 measurements.
Span = 6.4 KHz Y = 10 dB/div
52
Digital recording and
MP3 compressing
NATURAL TEST SIGNAL
В© K.Kuikka 2007
To bit rate 96 Kbps converted MP3 file
Signal: Natural_13_15
At the scope screen Natural Test Signal
has became extremely noisy.
Noise level is about 20 – 30 dB below the
level of Daughter Signals. In the picture
there is average test result of 30
measurements.
Span = 6.4 KHz Y = 10 dB/div
53
Conclusions
NATURAL TEST SIGNAL
В© K.Kuikka 2007
During testing measurements we noticed that Natural Test Signal is very easy to
use and effective test signal to carry out response error measurements.
Disadvantage of Natural Test Signal is that we must use expensive spectrum
analyser as an indicator.
In the future we ought to examine if it is necessary to measure only distortion
levels of fundamental frequency (275 Hz) and two times fundamental (550 Hz)
to find out the quality of a testing device.
If these two measurements are enough to find out the quality of a test device we
need only normal level meter and two narrow band pass filters (275 Hz and
550 Hz) to carry out distortion test. Indicator costs will then be very low.
Nowadays suitable indicator in not a problem any more. There are many
analyser software on the market so we can use normal personal computer as an
indicator when carrying out distortion tests with Natural Test Signal.
54
Testing equipments:
NATURAL TEST SIGNAL
В© K.Kuikka 2007
NATURAL TEST SIGNAL GENERATOR Model: ”Kuikka 2006”
TEKTRONIX TYPE 545B OSCILLOSCOPE
HEWLETT PACKARD 35660A DYNAMIC SIGNAL ANALYZER
FLUKE 8520A DIGITAL MULTIMETER
PHILIPS FA141 integrated stereo amplifier
CANON PowerShot A75 digital camera
Tests and measurements have been carried out by:
Kalervo Kuikka
OH6AWN
gsm: +358400 476231
55
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