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

3GB
GB
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