Sony DIGITAL NOISE CANCELING HEADPHONES... User manual

Product Information
3-280-434-21(1)
MDR-NC500D
©2008 Sony Corporation
Noise Canceling
Headphones
CT
GB
KR
CS

2GB

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Content
1. Introduction .......................................................................................................... 4
2. Principle of Operation of MDR-NC500D and Its Configuration ......................... 5
2.1. Feedback Type and Feedforward Type .......................................................................... 6
2.2. System configuration of MDR-NC500D ....................................................................... 7
2.3. Advantages of Digitization ............................................................................................ 8
3. AI Noise Canceling Function ............................................................................... 9
3.1. Operation of AI Noise Canceling function .................................................................. 10
4. Specialized Driver Unit ...................................................................................... 10
5. High-Quality Sound Unique to Digital .............................................................. 11
6. Weight saving mechanism .................................................................................. 12
7. Other Features .................................................................................................... 13
7.1. Monitor function .......................................................................................................... 13
7.2. Swivel mechanism ....................................................................................................... 13
7.3. Detachable connecting cord ........................................................................................ 13
7.4. Power supply ...............................................................................................................13
7.5. High-quality sound BTL headphone amplifier ............................................................ 13
Appendix: Indication of Canceling Performance
for Noise Canceling Headphones ....................................................................... 14
1.1. Total Noise Suppression Ratio .................................................................................... 14

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MDR-NC500D is the Digital Noise Canceling Headphones, which Sony developed as the
first of their kind in the world.
For this development, Sony put in all of its acoustical analysis technology, digital signal
processing technology and transducer technology.
By digitizing the noise canceling function, we succeeded in improving the performance in
the following points which, were difficult to be addressed with the conventional analog signal
processing:
•High canceling performance
•AI (Artificial Intelligence) Noise Canceling function
•Excellent sound quality
•Higher Signal to Noise ratio
1.Introduction

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2. Principle of Operation of MDR-NC500D
and Its Configuration
The noise canceling headphones make a canceling signal by analyzing with their noise
canceling circuit the surrounding noise collected by the small noise detection microphone built
in their main body.
With this canceling signal superimposed on the regenerative signal from the connected
equipment, reproduction from the driver unit reduces surrounding noise and makes it possible
to listen to music more clearly.
For the noise canceling, the following two methods are mainly used:
•Feedback type
•Feedforward type
1. Waveform of noise
(original sound)
Surrounding noise is collected by
the noise detection microphone
built in the headphones and its
signal is analyzed with the noise
canceling circuit.
2. Inverted sound
waveform
The inverted sound, which can
negate the analyzed noise, is
generated.
3. Sound waveform
canceled by
superimposition
By overlaying the original sound
with the inverted sound, the
original sound is negated. This
reduces noise at the eardrum.
Continued

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2.1. Feedback Type and Feedforward
Type
Feedback type
The noise canceling function of the “feedback type” is used in MDR-NC500D.
In the feedback type, the noise detection microphone is placed close to the ear.
By collecting noise in the position closer to the ear, a noise canceling effect with high
accuracy can be obtained.
The audio signal of noise collected by the noise detection microphone is analyzed on real
time with the noise canceling circuit (NC circuit), producing a canceling signal to always
minimize the noise at the eardrum. The canceling signal is reproduced from the driver unit.
Using this method enables the cancellation effect to be increased with the changing
environmental noise addressed.
Feedforward type
In the feedforward type, the noise detection microphone is attached outside the
headphones.
The NC circuit analyzes the noise signal collected by the noise detection microphone to
estimate what kind of sound the noise will become when it comes to the eardrum. And from
this estimated result, a canceling signal to minimize the noise is made and it is reproduced
from the driver unit.
This type enables miniaturization of the headphones since it is not necessary for the noise
detection microphone to be located near the ear where space is limited.
Feedback type Feedforward type
Noise
Driver unit
Noise detection
microphone
NC circuit
Noise
Driver unit
Noise detection
microphone
NC circuit

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Comparison between Feedback Type and Feedforward Type
Noise canceling effect
Anti dependency of noise
canceling effect against
individual difference / fitting
difference
Miniaturization
2.2. System configuration of MDR-NC500D
The Internal Block Diagram of MDR-NC500D is shown below:
The noise detection microphone of MDR-NC500D collects noise
around the ear.
The noise signal is digitized through the microphone amplifier and
high-speed A/D converter and is inputted in Digital Signal Processor
(DSP). Then the DNC software engine inside DSP generates the canceling
signal, which is inverted to the original noise.
Meanwhile, the regenerative signal of a music source supplied from
the audio input terminal is digitized by the high-speed A/D converter and is
inputted in DSP. Then, its frequency characteristic is adjusted by the digital
equalizer inside DSP. After the canceling signal is added, the regenerative
signal is reproduced as a sound by way of the high-speed D/A converter,
the headphone amplifier and the driver unit.
Mixing of the reproduced sound and the outside noise at the ear
negates only environmental noise, making it possible to enjoy music etc.
calmly.
Feedback type
Excellent
Better
Less suitable
Feedforward type
Good
Average
More suitable
Continued
Internal Block Diagram of Noise Canceling
Headphones of MDR-NC500D
Audio In
A/D
converter
System
controller
DSP
Digital
equalizer
Digital block
DNC software
engine
D/A
converter
A/D
converter
Detection
microphone
Headphone
amplifier
Driver unit
Microphone
amplifier
High-speed A/D,
D/A converter

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2.3. Advantages of Digitization
The performance of noise canceling headphones greatly depends on the efficiency of the
filter circuit (NC filter) between the microphone to detect noise and the driver unit to
reproduce the canceling signal.
In MDR-NC500D, the filter circuit for noise canceling is realized on the DSP as the
digital signal processing of the newly developed “DNC software engine.”
In addition to general advantages such as accurate computation results, no theatrical
variation, and no electric noise, the digital signal processing has also the advantage of making
it possible to create special filter shapes, which were not able to be realized with existing
analog filters.
During the development of the DNC software engine, the architecture of internal filter
computation was thoroughly examined in order to implement a more effective noise canceling.
The know-how of Sony’s digital sound treatment was used to construct a software engine
specialized in the noise canceling treatment and the calculation accuracy was heightened.
Noise canceling with less residual noise and higher Signal to Noise ratio was made possible.
Example of the characteristic of
conventional NC filter
Response
Frequency
Example of the characteristic of
digital NC filter
Response
Frequency

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The characteristics of environmental noise vary with the scene to be used.
In an airplane, for example, low and midrange frequencies can have a large noise energy
and other frequency ranges have a smaller noise energy.
On the other hand, in the environment such as an office, the noise energy is small but
distributed over a wider range.
In MDR-NC500D, the filter circuit to control a noise canceling ratio was digitized and it
is controlled by software.
This enables the filter characteristic to be switched: AI Noise Canceling function with
which MDR-NC500D selects automatically the filter characteristic (noise canceling mode) that
is the most suitable for the user's environment.
3.AI Noise Canceling Function
NC MODE A
Noise mainly in an airplane is effectively
reduced.
Frequency
Noise canceling ratio
*Manual mode selection is also possible.
AI Noise Canceling function
Digital technology allows selection from multiple
noise canceling modes.
The headphones analyze the outside noise and
automatically select the optimal canceling mode.
NC MODE B
Noise mainly in a bus or a train is effectively
reduced.
NC MODE C
Noise mainly found in an office environment
(PC, copier, air ventilation, etc.) is effectively
reduced.
Continued

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In order that feedback type headphones obtain
a wider canceling range, it is necessary to minimize
the time delay between the output of the driver unit
and the input to the noise detection microphone.
By integrating the noise detection microphone
with the driver unit to minimize the time delay,
MDR-NC500D achieved a stable and wider range
canceling performance.
Moreover, the use of re-informed diaphragm
significantly improved the canceling performance
against environmental noise with a high sound
pressure that is generated in a very low frequency.
3.1. Operation of AI Noise Canceling function
The operation of actual AI Noise Canceling function is as follows:
1. Press the AI NC MODE button to start the analysis program. *
2. Built-in DSP analyzes the sound information of noise from the noise detection
microphone.
Its specific value is extracted from the signal and the most effective noise canceling
mode is selected.
3. The noise canceling operation is started in the selected mode.
* During analysis, reproduction of music source and noise canceling function are temporarily stopped in order to
gather exact noise information.
MDR-NC500D completes the above-mentioned processing
in a short time of about 3 seconds.
The analysis algorithm of AI Noise Canceling (AINC)
developed a proprietary calculation technique based on the
Auditory psychology emphasizing the frequencies, which make
noise more audible to the ear.
It is the very realization of “smart headphones” which can
follow man's feeling.
With the AI Noise Canceling function only made possible
by Digital, please enjoy its comfortable canceling effect.
4.Specialized Driver Unit
DSP used in
MDR-NC500D
Driver unit

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MDR-NC500D digitized the NC circuit and used the digital equalizer in the playback
system.
The acoustical system of noise canceling headphones is generally based on the design,
which emphasizes low frequency in order to maximize the effect with limited electric power.
Moreover, in the case of the noise canceling headphones of feedback type, in principle
their music signal is impacted by the canceling function, so that the quality of the reproduced
sound is also impacted.
To solve these problems, an equalizer circuit is prepared in the audio input side.
The digital equalizer mounted in MDR-NC500D blocks the impact on the sound quality
and also brings about high-quality sound to maximize the intrinsic performance of the driver
unit.
By generously providing the digital equalizing technology accumulated with Sony’s AV
amplifiers and Hi-Fi audiovisual apparatus and using the newly developed computation
method optimized to the system, it was made possible to reproduce a music source with a
sense of realism from deep bass to silky highs.
5. High-Quality Sound Unique to Digital
Desired
characteristic
Characteristic of
acoustical system
Characteristic of
digital equalizer
Total
characteristic
Response
Frequency
Response
Frequency
Response
Frequency

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Magnesium and 7075 aluminum are used as the material for the housing and the
headband, respectively.
By using these unstintingly, the mass is reduced to as small as 195 g or more than 10 %
weight reduction. *
*In comparison with MDR-NC60.
6.Weight saving mechanism

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7.1. Monitor function
MDR-NC500D is equipped with the monitor function to make the surrounding sound
more audible by muting music etc. during reproduction when you are spoken to, for example.
While wearing the headphones, you can hear an announcement etc. in an airplane or in a
train only by pressing the button.
During monitoring, disturbing noise can be reduced by the noise canceling function.
7.2. Swivel mechanism
A mechanism to reduce the storage thickness by rotation of the housing is used in order to
enhance portability. (Swivel mechanism)
7.3. Detachable connecting cord
The main body side of the headphones connecting cord is detachable.
According to the equipment in combination, you can select the connecting cord of optimal
length from accessories. When using the noise canceling function without any music playback,
etc., disconnect the cord for comfortable use.
Moreover, the connecting cord with battery case also serves as power source.
MDR-NC500D can be used longer in combination with the built-in lithium ion
rechargeable battery.
7.4. Power supply
MDR-NC500D supports three kinds of power supply methods: Built-in lithium-ion
rechargeable battery, Alkaline LR03 (size AA) battery *1and AC power adaptor.
The AC power adaptor is of 100 V to 240 V multi-voltage type.
It can be used almost all over the world. *2
*1When the connecting cord with battery case is used. Two Alkaline LR03 (size AA) batteries are used.
*2Use with the outlet of a different shape needs an optional plug adapter.
7.5. High-quality sound BTL headphone
amplifier
The headphone amplifier is of BTL (Bridged Transformer-Less) type.
You can enjoy a powerful sound with a wide dynamic range.
7.Other Features

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1.1. Total Noise Suppression Ratio
Total Noise Suppression Ratio (TNSR) of noise canceling headphones is expressed with
the following formula:
TNSR = 10 log (P / P0)
•P
0= Energy of sound observed at the ear not wearing headphones
•P= Energy of sound observed at the ear wearing headphones
*The above energy of sound measurements are weighted.
TNSR is the value measured using the noise signal based on a broad spectrum.
As compared with the method of measuring the noise canceling ratio at a certain point of
frequency, TNSR enables the canceling performance in the actual usage environment to be
more objectively evaluated.
Moreover, it can evaluate the canceling performance in each noise environment by using
the signals to simulate the spectrum distribution of real-world noise such as an airplane and a
train.
Appendix: Indication of Canceling Performance
for Noise Canceling Headphones

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[Example of notation]
TNSR: 20 dB
[ Sony’s conventional method ]Noise canceling ratio = Difference between ON and OFF
Largest value (one point)
Sound pressure
Frequency
Wearing (OFF)
Wearing (ON)
Noise before
wearing
[ Total Noise Suppression Ratio (TNSR) ]
Sound pressure
Total Noise Suppression Ratio = Difference in noise energy
when not wearing the
headphones and when the
Noise Canceling function is
active.
Frequency
Total Noise Suppression Ratio (typical values)
Unit: dB
NC MODE A
NC MODE B
NC MODE C
Train/Bus
18.0
20.3
15.0
Office
17.1
18.3
18.9
Airplane
20.0
17.0
14.9
• Based on Sony's one noise source simulations.
•Note: Noise canceling ratio (Sony’s conventional method) more than 25 dB (at MODE A)

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目錄
1. 前言 ........................................................... 4
2. MDR-NC500D 工作原理及其組態 .................................. 5
2.1. 反饋型和前饋型 ..................................................... 6
2.2. MDR-NC500D 系統組態 .............................................. 7
2.3. 數位化的優點 ....................................................... 8
3. AI 防噪功能 .................................................... 9
3.1. AI 防噪功能操作 .................................................... 10
4. 專用驅動單元 .................................................. 10
5. 獨特的數位化高品質聲音 ........................................ 11
6. 減重結構 ...................................................... 12
7. 其他特點 ...................................................... 13
7.1. 監聽功能 .......................................................... 13
7.2. 旋轉結構 .......................................................... 13
7.3. 拆卸式連接線 ...................................................... 13
7.4. 電源 .............................................................. 13
7.5. 高音質 BTL 耳機放大器 ............................................. 13
附錄：防噪耳機防噪性能指標 ...................................... 14
1.1. 總噪音抑制率 ...................................................... 14

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MDR-NC500D 是由 Sony 研發的全球第一款數位防噪耳機。
對於此項研發，Sony 投入了其所有聲學分析技術、數位訊號處理技術和傳感器技
術。
通過數位化防噪功能，我們成功改善了以下性能，這些性能很難用傳統的類比訊號
達到：
•高防噪性能
•AI（人工智慧）防噪功能
•卓越的音質
•更高訊噪比
1. 前言

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2. MDR-NC500D 工作原理及其組態
防噪耳機由耳機內建的微型噪音檢測麥克風收集周圍噪音，並通過防噪電路進行分
析，從而生成防噪訊號。
將此防噪訊號疊加在所連接裝置產生的訊號上，從驅動單元再現的聲音將降低周圍
的噪音，從而使聽到的音樂更為清晰。
對於防噪，主要使用了以下兩種方法：
•反饋型
•前饋型
1. 噪音波形（原始聲音）
由耳機內建的噪音檢測麥克風收集
周圍噪音，並通過防噪電路對其訊
號進行分析。
2. 反向聲波
產生能消除被分析噪音的反向聲
音。
3. 重疊防噪後的聲波
通過用反向聲音覆蓋原始聲音，原
始聲音即被消除。這樣即降低了耳
膜中的噪音。
續下頁

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2.1. 反饋型和前饋型
反饋型
MDR-NC500D 中採用“反饋型”防噪功能。
在反饋型中，噪音檢測麥克風的位置靠近耳朵。
通過收集耳朵旁的噪音，即可獲得高精度的防噪效果。
由噪音檢測麥克風收集的噪音音頻訊號經防噪電路（NC 電路）即時分析，產生的
消噪訊號始終能減小耳膜中的噪音。消噪訊號由驅動單元產生。
使用此方法可使消噪效果隨環境噪音位置改變而增強。
前饋型
在前饋型中，噪音檢測麥克風安裝在耳機的外部。
NC 電路通過分析噪音檢測麥克風收集的噪音訊號，來推測噪音進入耳膜時將要變
成的聲音類型。根據推測出的結果生成減小噪音的防噪訊號，此訊號從驅動單元送出。
由於此類型不需要將噪音檢測麥克風裝在空間有限的耳朵旁，因此可以使耳機小型
化。
反饋型 前饋型
噪音
驅動單元
噪音檢測麥克風
NC 電路
噪音
驅動單元
噪音檢測麥克風
NC 電路