Analysis of the development and application of wireless audio technology

Broadly speaking, radio broadcasting is the earliest wireless audio technology, and it is also the most widely used, including FM, AM and so on. When it comes to these, you have to mention the radio.


Radio in early applications


Radio, whose full name should be radio waves, refers to electromagnetic waves in the radio frequency band that propagate in air or vacuum. It has a certain constraint on the frequency of the electromagnetic wave, wherein the upper limit is 300 GHz, and the lower limit is not limited. However, in general, there are three types of 3KHz-300GHz, 9KHz-300GHz, and 10KHz-300GHz.

As for the wavelength, the radio waves are all over 1 mm, which is much larger than the range of visible wavelengths we usually call. In addition, according to the difference in wavelength, it is further divided into long wave, medium wave, short wave, ultra short wave, microwave, and the like.

● The division of radio waves according to wavelength

Long wave: wavelength >1000m frequency 3000Hz-300kHz
Medium wave: Wavelength 100m-1000m Frequency 300kHz-3000kHz
Short wave: Wavelength 100m-10m Frequency 3MHz-30MHz
Ultrashort wave: Wavelength 1m-10m Frequency 30MHz-300MHz, also known as VHF wave, meter wave microwave: Wavelength 1m-1mm, frequency 300MHz-300GHz,

As for the application of radio waves, there are many aspects, such as communication (telephone, television), navigation, data transmission, astronomy (radio telescope), power, heating, and the like. Among them, a technique of propagating sound or other signals by radio waves is called radio technology.

The principle of radio technology is that changes in the intensity of the current in the conductor produce radio waves. Using this phenomenon, information can be loaded onto the radio waves by modulation. When the electric wave propagates through space to the receiving end, the electromagnetic field change caused by the electric wave generates a current in the conductor. By demodulating the information from the current change, the purpose of information transmission is achieved.

To say the earliest application of radio in sound, it is in navigation, the crew can use Morse telegram to communicate with the land, and use telegraph to convey various information. Subsequently, radio broadcasting was born at the end of the 19th century, and gradually became popular, becoming one of the main means for people to receive sound and receive various information.

Radio broadcasts are usually divided into two types, FM and AM. Among them, FM English name is Frequency Modulation, translated into Chinese is FM, is a modulation method. In FM radio, the audio signal is transmitted in the FM mode. The carrier of the FM wave changes on both sides of the carrier center frequency (the center frequency before modulation) as the audio modulation signal changes, and the frequency offset change and audio per second. The modulation frequency of the signal is the same. If the frequency of the audio signal is 1kHZ, the frequency offset of the carrier is also 1K times per second. The magnitude of the frequency offset is a function of the amplitude of the audio signal.

Although the original intention is FM, in daily life we ​​use FM to refer to FM radio. Generally speaking, the frequency band of FM broadcasting is between 76-108MHz, while the frequency band of FM broadcasting in China is 87.5-108MHz.

The English name of AM is Amplitude Modulation, which means amplitude modulation. It is also a modulation method and belongs to baseband modulation. The working principle is that the carrier frequency is kept constant, and the information is transmitted through the amplitude of the oscillation, which is exactly opposite to the principle of frequency modulation.

As for the advantages and disadvantages of both, we can feel from the brief features below:

FM AM

FM frequency modulation is not easily interfered, sound quality is good, sound quality is good, and it is easy to be interfered with. Two-channel stereo does not support two-channel stereo bandwidth. Wide bandwidth, narrow transmission power, low transmission power, low modulation, and complex reception are relatively simple.

It can be said that both have advantages and disadvantages. Therefore, they also have their own use. However, what we see in our daily life is more FM. Moreover, FM in the city uses FM, while international shortwave broadcasting and aeronautical navigation communication use AM.

Next, let's look at infrared technology. Before we say it, we must first understand what kind of infrared is.

Infrared is an electromagnetic wave having a wavelength between microwave and visible light, having a wavelength between 0.75 micrometers (μm) and 1 mm, and being spectrally located outside the red light. Infrared rays have a strong thermal effect and are easily absorbed by objects, and are often used as heat sources. In addition, its ability to pass clouds is stronger than visible light, and it has a wide range of uses in communications, detection, medical, military, etc., commonly known as infrared light.

Solar spectrum


● The discovery of infrared rays

In 1666, Newton discovered the spectrum and measured 3900 angstroms to 7600 angstroms (400 nm to 700 nm) as the wavelength of visible light. On April 24, 1800, William Herschel of the Royal Society of London (ROYAL SOCIETY) published that the sun has an invisible extension spectrum in addition to the red light in the visible spectrum, which has a thermal effect.

The method he used was very simple. Using a thermometer to measure the temperature of the light after splitting the prism, from purple to red, the temperature gradually increased. However, when the thermometer was placed outside the red light, the temperature continued to rise, thus determining There is the presence of infrared light.

● Division of infrared rays

Speaking of the division of infrared rays, it is currently complicated because the user's angle is different, and their division of the infrared frequency band is also different. For example, according to the infrared spectrum, the near-infrared should be 1 to 3 μm; and according to the medical use angle, the so-called near-infrared region is 0.76 to 3 μm.

The infrared division we are talking about is mainly divided into three parts, namely near-infrared, mid-infrared and far-infrared. The range of division is as follows: near-infrared rays, wavelengths between (0.75-1) and (2.5-3) μm; mid-infrared rays, wavelengths between (2.5-3) and (25-40) μm; far infrared rays, The wavelength is between (25-40) and l000 μm.

● Infrared is everywhere (unless absolute zero)

Just now, we have mentioned that infrared light has a strong thermal effect and is easily absorbed by objects, and is usually used as a heat source. In fact, there are countless far-infrared sources in nature: cosmic stars, the sun, the oceans of the earth, mountains, rocks, soil, forests, cities, villages, and various objects produced by humans.

At the moment, what we can be sure of is that all substances above absolute zero (-273.15 °C) can produce infrared rays! Among them, far infrared rays with a wavelength of 8~14μm are indispensable factors for biological survival. And this far infrared ray also has a separate name, called "life light wave.

Below, let's talk about infrared transmission. As I said earlier, infrared transmission is an existing technology that uses infrared rays as a carrier for data transmission. Here, we have to mention the two characteristics of infrared, because they directly determine the use of infrared transmission environment!

● Infrared penetration is weak

In general, the longer the wavelength, the weaker the penetration of the wave. Just now, we mentioned that infrared light has a stronger ability to penetrate clouds than visible light. But now, we are talking about penetrating thick obstacles. In this way, infrared transmission has privacy.

For example, if we carry out infrared transmission in a closed room in the room. Under normal circumstances, the next room is unable to intercept our infrared signals. This feature determines that infrared transmission is more suitable for conference rooms, classrooms, bedrooms and other places.

At the same time, infrared transmission mainly adopts a linear propagation form. Therefore, when an object is located between the transmitting end and the receiving end, the transmission is affected. Of course, it can be done by reflection from the wall. This does not seem to be a big problem for some other application scenarios, but it is unacceptable for audio, because it will cause data delay, which will cause the sound to be intermittent!

● Any object can emit infrared rays

This is easy to understand, all objects can emit infrared light. Then, for the infrared signal transmitting the data, interference can be generated. However, depending on the hot object, the interference is large or small. As a simple example, if you put a microwave between the transmitter and the receiver, or put a hot meal, it will have a major impact on the signal.

● Infrared transmission speed

Finally, let's mention the transmission speed of infrared rays. Here is a division: low-speed infrared (Slow IR) means that its transmission rate is 115.2Kbits per second, and high-speed infrared (Fast IR) means the transmission rate is per second. 1 or 4Mbits.

Among them, the former is mainly used to transmit short messages, texts or files. The most recent example from us is the various electrical remote controls in the home (when I was a child, it felt amazing, no matter what direction, click to control). The latter can support multimedia transmission, but it is still incomplete and still in the developing stage.

Summarize the characteristics of infrared transmission, advantages: good privacy, low cost, high-speed infrared development is more promising; disadvantages: not suitable for sharing, easy to interfere, delay, low-speed infrared is not enough to transmit audio.

Infrared transmission, as a wireless technology, has been applied to audio very early, but most of the transmitted audio is of poor quality. However, the Ramble IR amplifier released by the Rambler in 2008 completely broke the deadlock. Below, let's take a look at it, and also take a look at the application of infrared transmission technology in the audio field.

This is for Rambler to win the US 2008 CES Design and Engineering Innovation Award (Innovations 2008 Design and Engineering Award) and the German iF Product Design Award Industrial Forum Product Design Award - Ramble (foreign called Rainbow).

Ramble is a wireless infrared amplifier that is unique in its shape. It subverts the square shape of the traditional product and changes to a cylindrical shape. Moreover, the combination of silver and black is simple and generous, and it is very attractive. At the same time, its placement is also very random, it can be set up like this, or it can be hung on the wall, which is quite convenient. Among them, the left side is the Ramble receiver, and the right side is the Ramble transmitter.

Improved infrared wireless technology

Ramble's technical support comes from the improved infrared wireless technology. During the transmission process, it will undergo ADC conversion (analog to digital conversion), encode the signal into a digital string, and then transmit it to the power amplifier subsystem after receiving the DAC (digital to analog conversion). Its process is similar to S/PDIF fiber transmission, the transmission is no longer bound, and the sound quality is completely up to the CD level, that is, the level of 20-20 kHz. A set of fast fault-tolerant error correction audio is developed through a meticulous and efficient algorithm. The special mechanism makes this design truly real-time and ensures high sound quality.

In addition, Ramble uses three rows of 15 infrared emitters for infrared vertical emission. Then, through its diffuse reflection to complete the barrier-free connection. So, you don't have to worry about the interference of the obstacle between the transmitter and the receiver.

However, there are advantages and disadvantages. Because of the low penetration of infrared light, Ramble is currently only suitable for use in a room and not suitable for use in multiple rooms. And it's a stereo system, not a multichannel system. Therefore, it is not currently possible to build a wireless home theater. However, Mr. Zhang said that the rambler is working on audio transmission research of other wireless technologies. I believe that these two problems can be effectively solved in the near future.

In addition to infrared, Bluetooth is also a popular wireless audio technology. I believe most people are no strangers to this name, because there are many such devices around us, and the most typical ones are mobile phones and notebooks.

Bluetooth technology

Bluetooth, the English name is Bluetooth, is a radio technology that supports short-range communication of devices. Its earliest figure appeared in Ericsson's 1994 program, which was originally intended to study the method of low-power, low-cost wireless communication between mobile phones and other accessories. Moreover, they hope to develop a set of rules that provide a uniform standard protocol for communication between devices.

Multiple versions have been released so far

The Bluetooth project was launched in 1996 and the first application version was launched in 1998. Interestingly, the code for the original version was 0.7. Subsequently, Bluetooth technology continued to evolve, as of April 2009, Bluetooth has released multiple versions, the latest is Bluetooth 3.0 + HS. In the meantime, on May 20, 1999, industry leaders such as Sony Ericsson, IBM, Intel, Nokia and Toshiba established the Bluetooth Technology Alliance (SIG) to jointly develop Bluetooth technology standards.


As mentioned before, the version of Bluetooth is really too much, and the protocol of each version, we have not studied too deeply. However, as far as application is concerned, we are familiar with versions 1.1, 1.2, 2.0 and 2.1. Therefore, the working principle and features of Bluetooth described below are all based on the protocols of these versions.

Bluetooth protocol stack architecture diagram

The first thing to be determined here is that the Bluetooth application is on the global 2.4GHz band, and the WiFi and 2.4GHz that we will talk about later are all working in this band. Bluetooth is divided into 79 sub-bands in the 2.4 GHz band. During operation, Bluetooth will select the frequency hopping between the 79 1 MHz channels, and rely on short packet technology for communication.

While Bluetooth technology works, it uses a decentralized network structure, namely, high-speed frequency hopping (FH, Frequency Hopping) and time division multiple access (TDMA, Time Divesion Muli-access) technology, which will be the cheapest at a short distance. Several digital devices (various mobile devices, fixed communication devices, computers and their terminal devices, various digital data systems, such as digital cameras, digital cameras, etc., and even various household appliances and automation devices) are linked in a mesh.

As for the transmission distance, Bluetooth is a short-distance transmission technology, and its transmission distance is generally within 10 meters. However, Bluetooth has a little advantage, that is, the power is low, so the Bluetooth adapter we are currently seeing is generally not big.

Next, we will briefly introduce you to the 1.1, 1.2 and other versions of the agreement just mentioned.

Bluetooth hands-free hardware circuit diagram

1.1 The specification is mainly for some shortcomings of the 1.0 specification. One of the points is to determine the master/slave relationship of the device in the callback, which can improve the accuracy of communication. In addition, the 1.1 specification clarifies that Bluetooth technology communicates on 79 sub-bands, while previously there were two divisions, 79 and 23.

The biggest improvement in version 1.2 is the addition of AFH's Adaptive Frequency Hopping technology, which is a comprehensive improvement to the mutual interference between the existing Bluetooth protocol and 802.11b/g, preventing users from Mutual interference occurs when using both devices that support Bluetooth and Wireless Local Area Network (WLAN).

In contrast, the 2.0 version has a bigger improvement. It not only improves the multitasking capabilities of the device, but also improves the ability of multiple Bluetooth devices to run simultaneously. In addition, the bandwidth has also been greatly improved, and its theoretical value has been increased from the original 1Mbps to 3Mbps.

But now we are common to the 2.0+EDR standard, which improves the data transfer rate and reduces power consumption based on the original 2.0 version. Moreover, the problem of concatenation of multiple Bluetooth devices is also specified. In this way, the transmission distance is theoretically expected to hit 100m, and the rate can reach 10Mbps.

Bluetooth 3.0 protocol

Subsequently, the 2.1 agreement was released. For it, we know less, and the difference between it and 2.0 is not very clear, but we can know that the 2.1 version of the protocol reduces power consumption again.

Finally, let's talk briefly about the 3.0 version of the Bluetooth protocol: it uses the new alternate RF technology of the Generic AMP (Gener ic Alternate MAC/PHY), allowing its protocol stack to dynamically select the correct RF for the task. In addition, the 3.0 new standard's short-distance transmission rate will reach 24Mbps (theoretical value). Moreover, this value can be increased to 480 Mbps through ultra-wideband technology, and the transmission rate can be increased to 100 Mbps when the distance is 10 meters.

Having said that, we have to rely on the topic: wireless audio. Bluetooth is a wireless technology, but we are talking about its application in audio transmission.

First look at the bandwidth, the theoretical value of the bandwidth in the Bluetooth 1.1 and 1.2 protocols is 1Mbps, but in practical applications, it is generally 748-810kbps. By the 2.0 protocol, the theoretical value of the bandwidth has reached 3 Mbps, and in practical applications it is about 1.8 Mbps to 2.1 Mbps. The current highest is the 3.0 protocol. As we said before, the theoretical bandwidth can reach 24Mbps.

I have to mention the A2DP protocol here, because the earlier version of the Bluetooth protocol, although it can be used for wireless data transmission, has little support for audio - only supports mono audio transmission, and sampling Only 8bit/8KHz is supported. This situation was not changed until A2DP was added.

The full name of A2DP is Advanced Audio Distribution Profile, translated into Chinese: Bluetooth Audio Transmission Model Agreement! Its main contribution is the addition of support for high-quality sampling, which enables Bluetooth technology to support 16bit/44.1kHz.

In addition, A2DP also provides detailed definitions from the encoding and decoding of audio signals, to the interactive interface, to video encoding. Among them, it allows Codec to support MP3, MPEG2, MPEG4 AAC, ATRAC and other video and audio encoding.


Currently, the theoretical bandwidth required to transmit CD-level signals is 1.4112 Mbps, so Bluetooth devices after the 2.0 protocol are capable. However, there are very few Bluetooth audio devices with good sound quality. We think this is mainly because manufacturers and chip providers do not work hard.

Well-known Jabra Bluetooth headset



In addition, Bluetooth's anti-interference ability is weak. As we said earlier, Bluetooth is operating on the 79 average spaced sub-bands in the 2.4 GHz band. At present, there are many Bluetooth devices around us, so it is easy to cause interference.

However, Bluetooth also has an advantage, that is, after so many years of development, the technology maturity is still very high. But as I said just now, I don’t have to worry about what I’m doing. Therefore, the Bluetooth audio devices we are currently seeing are mostly cheap. And there is still a part, which is a high-end product, very high-end, very expensive.

Typical Bluetooth and low power Bluetooth



Finally, when we collected and organized the data, we also found that Bluetooth also has some settings for low power consumption. The above table is some of the differences between typical Bluetooth and low-power Bluetooth technology. Among them, the most obvious one is in use: low-power Bluetooth is less used on stereo audio streams.

● Conclusion

Bluetooth is still the most widely used technology in wireless audio, and it is also the most common technology around us. Its advantages are cost and technical maturity, but there are fewer good products, mainly because of the need to do it. Nowadays, 2.4G technology has begun to rise and is gradually being applied by ordinary products. Therefore, the status of Bluetooth in wireless audio will be a strong challenge of 2.4G technology. The result is naturally good, that is, we will definitely get the best product!

Say WiFi! The full name of WiFi is: Wireless Fidelity. At present, the popular saying is: WiFi is a wireless technology, mainly used for network connection. This statement is not wrong, because we usually contact the most wireless routers, which is characterized by the use of WiFi technology to form a network.

However, this statement is not rigorous. First of all, WiFi is a technology that can connect terminals such as personal computers and handheld devices (such as PDAs and mobile phones) wirelessly, rather than simply building a wireless network.

Second, WiFi is a brand of wireless network communication technology, hosted by the Wi-Fi Alliance, to improve interoperability between wireless network products based on the IEEE 802.11 standard. Therefore, the WiFi and IEEE 802.11 standards are not completely equated.

Having said that, we have to add something about the IEEE 802.11 standard - the first version of IEEE 802.11 was published in 1997, which defines the medium access control layer (MAC layer) and the physical layer. The physical layer defines two wireless frequency modulation methods and one infrared transmission method working in the 2.4 GHz ISM band, and the total data transmission rate is designed to be 2 Mbit/s. The communication between the two devices can be performed in an ad hoc manner, or in coordination with a base station (BS) or an access point (AP).

Mainly used for wireless networks

In 1999, the IEEE 802.11 standard added two additional versions: 802.11a defined a physical layer with a data rate of 54 Mbit/s on the 5 GHz ISM band, and 802.11b defined a 2.4 GHz ISM band. A physical layer with a data transfer rate of up to 11 Mbit/s.

The 2.4 GHz ISM band is common to most countries in the world, so 802.11b is the most widely used. Apple named the 802.11 standard it developed as AirPort. In 1999, the industry established the WiFi Alliance to address the production and device compatibility issues of products that comply with the 802.11 standard. WiFi is an organization that develops 802.11 wireless networks and does not represent wireless networks.

Like other technologies, the IEEE 802.11 standard has undergone continuous improvement and supplementation to form the scale of this technology application.

● 802.11 standards and supplements

802.11 In 1997, the original standard (2Mbit/s, 2.4GHz channel).
802.11a In 1999, the physical layer was supplemented (54 Mbit/s, 5 GHz channel).
802.11b In 1999, the physical layer was supplemented (11 Mbit/s, 2.4 GHz channel).
802.11c is 802.1D compliant Media Layer Control (MAC) Bridging.
802.11d Adjustments made in accordance with national radio regulations.
802.11e support for Quality of Service (QoS).
Interoperability of 802.11f base stations.
802.11g physical layer supplement (54Mbit/s, 2.4GHz channel).
802.11h wireless coverage radius adjustment, indoor (door) and outdoor (outdoor) channel (5GHz band).
A supplement to 802.11i security and authentication (Authentification).
802.11n introduces multiple input and output (MIMO) and 40Mbit channel width (HT40) technology, which is basically an extended version of 802.11a/g.

In addition to the above IEEE standard, there is another technology called IEEE 802.11b+, which provides a data transmission rate of 22 Mbit/s on the basis of IEEE 802.11b (2.4 GHz band) by the Packet Binary Convolutional Code. But this is not actually an open standard of the IEEE, but a proprietary technology (ownership belongs to Texas Instruments, Texas Instruments).

In addition, there are some technologies called 802.11g+, which provide 108Mbit/s transmission rate based on IEEE 802.11g. Like 802.11b+, it is also a non-standard technology. SuperG is promoted by wireless network chip manufacturer Atheros. .


Ok, let's take a look at the application of WiFi technology in wireless audio. First of all, bandwidth is absolutely absolutely no problem: what we see today is mostly 802.11g and 802.11n devices, while the former has a theoretical bandwidth of 54 Mbps and the latter has a theoretical bandwidth of 300 Mbps, which is much higher than transmitting CD-level signals. The required 1.4112Mbps.

In addition, WiFi also has a clear advantage in the transmission distance. In the front, we have introduced that the transmission distance of Bluetooth is about 10m. However, WiFi is 10 times its size, which is about 100m. Therefore, WiFi can be applied to some large scenes, such as large conference rooms.

Linksys Wireless Music Bridge

But WiFi also has its own drawbacks, mainly here is the problem of interference. Because WiFi is also working on the 2.4GHz-2.48 GHz ISM RF band. Among them, it is used in one of 12 overlapping channels in the 22MHz bandwidth. In this way, conflicts with other WiFi devices, even Bluetooth and 2.4G devices, cannot be avoided.

There is another point, but we haven't verified it carefully. It is rumored that the wireless communication quality transmitted by WiFi technology is not very good, and the data security performance is worse than Bluetooth. At the same time, WiFi seems to be slightly more delayed.

Therefore, the prospect of WiFi for wireless wireless transmission is good. In particular, the advantages of bandwidth and distance add a competitive edge to WiFi. However, there are still very few devices that use WiFi at present, and manufacturers need to pay more attention!


Among the many wireless audio technologies, it is currently optimistic, and it is most likely that 2.4G technology is used in large areas in ordinary audio equipment.

Pennefather H8000 Wireless Headset

The 2.4G technology is exactly the same, it should be called "2.4GHz non-networking solution." The reason for this is very simple, because it works like the Bluetooth and WiFi, and works on the 2.4-2.485GHz ISM radio band. This band is almost exclusively licensed for free worldwide. Therefore, there are some advantages in product cost, which will help the large-scale popularization of products.

However, the product receiving end and the transmitting end using the 2.4G technology are built with a pairing ID code to form a one-to-one mode. Therefore, the receiving end and the transmitting end between different brands and different products cannot be mixed, which greatly limits the use and popularity of the technology in other fields. At this point, 2.4G technology is not as flexible as Bluetooth.

In fact, friends who have been paying attention to our series of articles will find that more than 2.4G technology works in the 2.4-2.485GHz ISM wireless band - Bluetooth and WiFi, which we have just explained, also work in this frequency band. So, what are the differences between 2.4G technology and theirs?

The first is bandwidth. The 2.4G technology has a bandwidth of 2 Mbps and is capable of transmitting CD-level wireless audio signals. In contrast, versions after Bluetooth 2.0 can reach and far exceed this number. As for WiFi, let alone, its bandwidth is higher.

In addition, the transmission distance of 2.4G technology is 10m, which is similar to Bluetooth, but close to WiFi. However, a distance of 10m is enough for ordinary consumers to use at home. Moreover, the transmitter and receiver of a 2.4G device do not require continuous operation. So, relatively speaking, it is more energy efficient.

But among many differences, 2.4G technology has a very advantageous advantage - that is, the anti-interference ability is better than Bluetooth and WiFi. This is mainly due to the working principle and the reasons for the frequency modulation method adopted.

2.4G technology uses automatic frequency modulation technology, which is easy to understand - it means that when the 2.4G device is working, if it is found that the frequency band is often occupied, it will automatically jump to an unused frequency band. The method of frequency hopping is very random.

SE8 High Fidelity Wireless Speaker Adapter

Bluetooth is an adaptive 2.4G wireless technology that adds adaptive frequency hopping (AFM) to achieve full-duplex transmission mode and achieve automatic frequency modulation of 1600 times/second. However, we have also said that Bluetooth divides the 2.4-2.485 GHz ISM into 79 sub-bands equally, so its frequency hopping is also performed in these 79 frequency bands. Therefore, it is still prone to mutual interference.

As for WiFi, it is used in one of 12 overlapping channels in the 22 MHz bandwidth in the 2.4-2.485 GHz ISM band. Therefore, its optional surface is narrower and relatively prone to interference.

At present, in terms of technology maturity, Bluetooth is undoubtedly the most advantageous position in wireless audio. However, 2.4G technology is not to be outdone, and is gradually entering a period of stability and maturity. There are already a variety of wireless audio solutions using 2.4G technology. Moreover, the products are gradually enriched.

Among them, there are more earphone products, and there are representative Leibo and charm in China. In particular, Leibai, its 99 yuan 2.4G headset H1000 has been on sale recently, with a large sales volume.

In addition to these, Leibai also introduced a 2.4G wireless adapter for speaker use. Although, we have not seen its real products yet, but with the emergence of these 99 yuan wireless headsets and speaker-specific wireless adapters, the era of widespread wireless audio is coming soon!

Above we talk about FM, AM or 2.4G technology, but also some of the wireless audio technology we are familiar with. Then, let's introduce some new technologies that are not common and future-oriented!

First look at RF radio technology, the full name of the radio frequency in English is: Radio Frequency, which represents the electromagnetic frequency that can be radiated into space, the frequency range from 300KHz-30GHz. The RF radio we usually call is actually the RF current, which is an abbreviation for high-frequency AC-changing electromagnetic waves.

In practical applications, AC power that changes less than 1000 times per second is called low-frequency current, more than 10,000 times is called high-frequency current, and radio frequency is such a high-frequency current. Our familiar cable TV system uses RF transmission. .

Wireless magic box that is about to stand out

In fact, RF technology is not new, but a very non-old technology. RF technology has a lot to do with what we call wireless transmission: the source of electrical information (analog or digital) is modulated with high-frequency current (amplitude or frequency modulation) to form a radio frequency signal that is transmitted through the antenna into the air; After the RF signal is received, the RF signal is inversely modulated and restored to an electrical information source. This process is called wireless transmission, where RF RF technology is applied.

However, at present, we have very little information on RF technology, but it is known that its transmission distance is far away. Recently, the RF wireless box has been developed for audio transmission, and its transmission distance. It is 50m, far more than Bluetooth, 2.4G, etc. As for its bandwidth and interference issues, we have not studied it.

DAB digital broadcasting is also currently being applied to wireless audio transmission technology, but it is currently mainly popular in Europe, while domestic use is relatively small, but in Beijing, Guangdong and other places have already adopted DAB broadcast.

DAB is the abbreviation of Digital Audio Broadcasting. Its DAB is the third generation of broadcasting after the traditional analog broadcasting of AM and FM - digital signal broadcasting. Its emergence is a revolution in broadcasting technology. Digital broadcasting has the advantages of anti-noise, anti-interference, anti-wave propagation fading, suitable for high-speed mobile reception and so on. It provides CD-level stereo sound quality with almost zero distortion of the signal, which can achieve "crystal clear" audio-grade sound quality, especially suitable for broadcasting "classical music", "symphonic music", "pop music", etc. Professional musicians, music enthusiasts and audiophiles are sought after! Moreover, it is not affected by multiple path interference within a certain range to ensure high quality of fixed, portable and mobile reception.

Compared to analog broadcasting, DAB has two of the biggest features of digital broadcasting. One is bandwidth, and DAB can transmit any text or even image signals. Therefore, you don't have to worry about its quality. It is reported that the signal-to-noise ratio of DAB broadcast is at least 95db, and the coding rate is 192Kbps, far exceeding the average MP3, which is close to the sound quality of CD.

The second is the digital signal transmission anti-jamming and anti-radiation attenuation characteristics, DAB broadcast is very suitable for use in a fierce mobile environment, such as car.

In this regard, if 2.4G technology is most suitable for ordinary civilian-grade equipment and is suitable for small-scale use, then DAB digital broadcasting is suitable for high-quality audio transmission in a wide area. However, this requires a comprehensive change to the current broadcasting system. This is a big project and it is very difficult and troublesome.


Next, let's look at three emerging wireless technologies: UWB, WiHD, and WDHI.

UWB, its full name is UltraWideband, Chinese translation: super too wide. It is a carrierless communication technology that uses a non-sinusoidal narrow pulse of nanoseconds to picoseconds to transmit data. Moreover, it can transmit very low power signals over a wide spectrum - UWB can achieve data transmission rates of hundreds of Mbps to several Gbps in the range of about 10 meters.

It is reported that UWB has many advantages such as strong anti-interference performance, high transmission rate, wide bandwidth, low power consumption, and small transmission power. Moreover, UWB can use frequencies above 1 GHz to multiple GHz. It is not difficult to see that UWB technology has a very eye-catching performance in all aspects, so some people call it a revolutionary development in the field of radio, which it believes will become the mainstream technology for short-range wireless communication in the future.

In addition, UWB technology can be used in conjunction with other wireless technologies to increase the bandwidth of the transmission. For example, Bluetooth 3.0 can be extended by UWB technology - the theoretical value of the original 24Mbps bandwidth is raised to 480Mbps, and the transmission rate can be increased to 100Mbps when the distance is 10 meters.

As for the WiHD and WDHI technologies, they are different from the wireless audio technology we mentioned above - they are no longer transmitting audio signals, but transmitting "audio/video" signals.

WiHD, English full name WirelessHD (Wireless HD, abbreviated as WiHD) technology is a high-speed wireless technology that users expect, mainly because it uses the spectrum of 60GHz band (millimeter wave) to achieve greater data transmission rate. Its initial transmission rate is as high as 4Gbps, which makes it more reliable to provide the bandwidth necessary to transmit high-quality, high-definition uncompressed video.

The leading manufacturers of WiHD standards include Intel, LG, Panasonic, NEC, Samsung, SiBEAM, Sony, Toshiba and other industry leaders. The standard is aimed at HDTV sets, set-top boxes, DVD players, digital cameras and game consoles. HTPC, etc., allows consumers to transfer, play and carry high-definition content between multiple electronic devices.

目前,WiHD 1.0 Specification技术规范已经发布,其确立了无线高清的基本标准,通过智能天线技术的运用可克服60GHz下的视线限制问题,并加强了数字传输内容保护(DTCP),得到了众多国际性消费电子制造商的支持,支持真正的无压缩视频流传输,强制性的使用了通用控制技术,用户可以容易的构建和管理自己的无线视频局域网(WVAN),传输距离10米内。

WHDI,意为Wireless HDMI,中文意为无线高分辨率数字多媒体接口。它也是一种针对于高清的无线技术,而其主要的做法,就是将超宽带技术与HDMI技术相融合。另外,WHDI主要利用的是5GHz的频带,数据传输速度最快可达1.5Gbps。充足的带宽,可以使WHDI可以传输720P/1080i的非压缩HDTV影像。

支持WHDI的微处理芯片

另外,WHDI的传输距离较远,且穿透力很强。其支持采用Deep Color(深色)技术的1080p/60Hz全高清显示,有效传输距离为30m。而且,其在30米之内可穿透墙壁,影响极小——延迟小于1毫秒。

而且,WHDI指定了高清视频传输,以及音频和控制。全面WHDI控制协议将使用户能够集中控制从家庭中的所有A/V设备,传输几乎没有延迟,用户不会遇到声音和视频异步的问题,也可以利用WHDI连接网络娱乐音频视频游戏。



"Lithium battery" refers to a battery made of lithium metal or lithium alloy as a negative electrode material, using a non-aqueous electrolyte solution.It has a high energy density.Compared with high-capacity nickel-cadmium batteries, the energy density is twice as high.High voltage. The average service voltage is 3.6v, which is three times higher than nickel-cadmium and nickel-hydride batteries.The use voltage is even and the high capacity, the widespread use temperature -20 degrees -60 degrees, the charge and discharge life is long, after 500 discharges its capacity at least has more than 70%.Due to the characteristics of high energy density, high voltage and stable operation, lithium battery is widely used.

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