Nowadays, there are a variety of wireless audio connection solutions for us to choose. Since Bluetooth 1.0, the industry has tried to use this wireless standard to solve the connection between music and players. The earliest Bluetooth 1.0 era was limited by bandwidth. It can transmit single-channel audio signals, and the encoding rate is very low. It is only slightly better than the sound quality of the phone. The power of the Bluetooth 1.0 standard is very small. If the distance between the audio source and the player is slightly longer, the connection will be lost, so Bluetooth wireless only As an auxiliary device for the phone, listening to music still requires the use of wired headphones to enjoy high-quality sound effects, which is why Apple still provided a pair of headphones with average sound quality long ago.
With the development of the Bluetooth standard, both bandwidth and power have been greatly improved. With the support of the new standard, the industry has begun to fiddle with Bluetooth headsets. In order to improve the sound quality of Bluetooth headsets, each major manufacturer will launch its own Bluetooth audio protocol, although the Bluetooth Standard Association originally considered audio applications when it formulated the Bluetooth standard, it is the Bluetooth audio transmission protocol developed by these major manufacturers that brings better sound effects. The mainstream audio There are four audio transmission protocols SBC (Sub-band coding, sub-band coding) ACC (Advanced Audio Coding) APTX LDAC.
SBC (Sub-band coding, sub-band coding)
The earliest format should be SBC, and SBC is a coding format mandated by the A2DP (Advanced Audio Distribution Profile, Bluetooth Audio Transmission Protocol) protocol. All Bluetooth will support this protocol, so all Bluetooth audio chips will also support this protocol.
ACC (Advanced Audio Coding, Advanced Audio Coding)
ACC is a technology provided by Dolby Laboratories for the music community. It is a coding algorithm with a high compression ratio. In actual experience, it is believed that at the same bit rate, ACC has a better listening experience than MP3, and there are many ACC audio on Apple. Therefore, the current iPhone audio transmission format is also acc format, the bit rate is equivalent to SBC, but the listening experience is said to be better than SBC. When Bluetooth supports files in AAC format and mobile phones also support AAC transmission, the sound quality is much better than SBC.
APTX
APTX is a patented coding algorithm of CSR. After being acquired by Qualcomm, APTX has been widely promoted in Android phones.
There are three types of aptX: aptX, aptX HD and aptX Low Latency
According to the name, they are traditional aptX, high-quality aptX and low-latency aptX. Therefore, the transmission rate of aptX is actually not high. It may be similar to the previous two. However, thanks to the efficient encoding, the sound retains more details. The actual listening experience is better than the previous two. A sense of hearing that reaches the CD level.
To support APTX, you must purchase this software fee, and aptx is not supported by most mobile phones. Generally, the supported mobile phones have the aptx logo on the back, so although the effect is good, there are actually not many devices that can be supported.
LDAC
LDAC is an exclusive agreement of SONY Dafa (except for SBC are exclusive agreements), SONY has increased the channel simply and rudely. On devices that support LDAC, the Bluetooth communication bit rate is close to 1M.
LDAC can transmit about 3 times the data of ordinary Bluetooth (at a transmission speed of up to 990kbps), allowing you to listen to Hi-Res Audio music wirelessly, and you can hear close to *Hi-Res Audio * The sound quality.
With such a high transmission speed, it is possible to transmit lossless music. Of course, the transmission format of this kind of almost proprietary protocol also causes only a small number of devices to be compatible now. But there is no doubt that LDAC has been greatly improved in transmission rate, which makes the transmitted audio quality higher and the listening experience is naturally the best
So do we still need wire connection equipment?
The agreements mentioned above are almost all exclusive agreements of major manufacturers. To use these agreements, you need to spend money to buy licenses. Among them, APTX is supported by Qualcomm. At the same time, Qualcomm is also a member of the Android Alliance. The level of promotion of the APTX standard is almost free to use on the Android platform. Of course, the premise is that you have to have a pair of headphones or playback devices that support the APTX protocol. This part of Qualcomm You can charge a fee. The LDAC standard launched by SONY can only be used on SONY's own equipment.
Although the agreement is chargeable, it is not too expensive and is usually acceptable to consumers. So can we abandon the wire and embrace wireless? If you just listen to the sound, then you can definitely abandon the wire, Bluetooth wireless is enough to meet your needs. But if you have requirements for sound quality, don't throw away your expensive cables, because the sound quality of wireless transmission can never be compared with wired in theory.
Encoding format, bit rate and transmission rate restrict the sound quality
So why can wireless encoding never catch up with wired connections? This is about encoding, bit rate and transmission rate.
Encoding
The SBC APTX LDAC AAC mentioned above are all encoding formats. These are actually irrelevant to the use of wired or wireless. These encoding protocols can still be used even for wired connections. .
The encoding is also divided into two formats, lossy encoding and lossless encoding. Usually lossy encoding can provide a larger compression ratio, just like the MP3 encoding format is lossy encoding, compression The rate can reach 1:100, which is why MP3 once dominated the Internet music format, because its size is too small. However, lossy coding comes at the expense of sound quality, because although the sound that human ears can discern is theoretically 20~20KHz, usually sounds below 100Hz and above 15KHz are almost inaudible to human ears, so there is Loss coding filters out this part of the frequency through an algorithm. After removing this part of the frequency, the size of the sound file will be reduced a lot, but after losing this part of the frequency, the music atmosphere we feel will be very different. Lossless compression is necessary for the transmission of sound signals in a wireless system, otherwise the bandwidth of wireless transmission cannot be tolerated at all.
Bit rate
What I mentioned above is the encoding format, and then the bit rate. Even if the bit rate is different, the sound effect of the same encoding method will vary a lot. For example, the commonly used MP3 format used a bit rate of 64kb/s in order to obtain a smaller file in the early days. Basically, this bit rate is just to hear a sound. If it is better, the bit rate will be set to 128kb/s, At that time, it was considered high-fidelity music, and the current bit rate must be at least 256kb/s or 512kb/s to be considered high-fidelity music, and some lossless encodings even have a bit rate of 1Mb/s. It is conceivable that the transmission protocol of Bluetooth 5 is currently only 2Mb/s, but it is still impossible to squeeze the bandwidth of Bluetooth. This reason will be explained in the following Transmission rate.
The original uncompressed WAV music code rate can reach 10Mb/s or even higher, which can only be achieved on Blu-ray players.
Transmission rate
Now let’s talk about the transmission rate of Bluetooth. The currently announced Bluetooth 5 standard has a transmission rate of up to 2MB/s. Don’t think that this rate is very low, because the Bluetooth standard is targeted for IOT devices, and their own needs are occasional transmission. Some data, but it must be able to achieve long-term standby. Under such requirements, the goal of saving electricity can only be achieved by reducing the transmission rate. It is also because of the advancement in battery technology that the Bluetooth transmission rate can be adjusted to the height of 2MB/s.
But this transmission rate is actually derived from the theoretical situation. To achieve a transmission rate of 2MB/s, you must maintain a distance of 1 meter from the device, and at the same time, there must be no interference from other radio signals, and there must be no space where you are. The material that reflects the radio. Only laboratories or specially built audio-visual rooms can meet such conditions.
But now our living environment is full of radio signals, especially the frequency bands used by WiFi and Bluetooth are the same, both 2.4GHz and 5GHz (because these two frequency bands do not require government review in the world ), so the actual transmission rate will not reach the highest rate. At the same time, in order to achieve signal error correction, filter the interference of reflected waves and increase the use distance, the actual transmission rate we can use is much lower than the theoretical nominal value. So even if you use a better encoding format and a higher encoding rate, but the final wireless transmission rate cannot meet the requirements, high-fidelity sound cannot be transmitted.
Final conclusion
Because wireless transmission inherently has such shortcomings, if your requirement for sound is to listen to a sound, then you can choose wireless connection steadily. If your requirements are relatively high or professional high music, then it is still Continue to use the wired connection, because the transmission rate and coding rate of the wired connection have reached infinity.