Apple issued a news last week that Apple Music started to support Dolby Atmos and lossless music in June. Dolby Atmos supports all Beats headsets with AirPods and H1 and W1 chips. Because of the special lossless sound quality, they issued a separate long announcement the day before yesterday, about the following points: 1. All AirPods, AirPods Pro, AirPods Max, Beats headsets do not support the lossless sound quality of Apple Music. 2. Even if the adapter is plugged in, AirPods Max cannot hear losslessly, because data signal conversion will occur and there will be data loss. 3. HomePod and HomePod Mini will support lossless sound quality through software updates later. Netizens were anxious as soon as this announcement came out. They couldn’t hear their own lossless music with their own headphones. Funny words? Don’t get excited, when Apple didn’t produce lossless music before, don’t you also think AirPods are very fragrant. . In fact, Apple cannot be blamed for this. Most Bluetooth headsets on the market cannot support lossless music with current technology. Why do you say that, let’s first understand a few concepts. After the singer has finished recording the song, he must make the music analog signal into a music file through PCM encoding, which is digitized. The encoded file is called a PCM file, which is the most basic audio encoding, and all encoding operations need to be based on the PCM format. But this kind of file often cannot be played directly. It needs to be re-encoded in order to be heard by the public. There are three ways: Uncompressed encoding (common formats are AIFF, WAV) Lossless compression coding (common formats are WMA, FLAC, ALAC) Lossy compression coding (common formats are MP3, AAC) Due to the large volume of uncompressed encoded files, a few songs can be used as a small movie. In order to facilitate storage, everyone usually comes into contact with compressed music files, which is often referred to as lossless and lossy music. If a song “Hotel California” uses uncompressed encoding Its file size is 264 MB I don’t know if you will notice 128K and 320K when you download MP3 before. These numbers are the audio bitrate. The bit rate represents the data transmitted per second by the audio. The higher the bit rate, the better the sound quality. The code rate is determined by the sampling rate, bit depth, and the number of channels. Without compression, the code rate = sampling rate * bit depth * number of channels. Sampling rate indicates the number of sound samples collected in 1 second, and the unit is Hz. The sampling bit depth indicates the accuracy of each collected sound sample, and the unit is bit. Sound channels, for example, the number of channels for dual channels is 2. According to the international definition, the sound quality must reach the CD level to be considered lossless, that is, the sampling frequency is 44.1 kHz and the sampling bit depth is 16 bits. But in fact, a large part of Bluetooth headsets can’t handle even this most basic lossless music. According to the code rate formula just now, the code rate of the dual-channel 44.1kHz/16-bit music without compression is: 44.1kHz * 16 * 2 =1411.2 kb/s (note here b is a bit, not a B Byte, 1B = 8b) Usually the compression rate of lossless music is 70%, and the bit rate of lossless music is about 1411kb/s * 70% = 987 kb/s. In other words, to transmit lossless music, the transmission bandwidth is 987 kb/s. The reason why it is difficult for Bluetooth to support lossless music is because the bit rate of common Bluetooth encoding format (SBCAAC) is not enough, basically at 328 kb/s. So even if you listen to lossless music with a bitrate of 987 kb/s, it will be compressed to 320 kb/s when you encounter these Bluetooth encoding formats, and when it is converted back, it is no longer lossless music, let alone Let’s talk about the loss that occurs in the analog-to-digital conversion. At present, only Sony’s LDAC and Shengwei LHDC are the only Bluetooth codecs that can achieve lossless music bit rates, which can reach a maximum of 990 kb/s. Without considering the audio loss in the analog-to-digital conversion, they can barely transmit lossless music. However, these two encodings are not yet popular, and to use these two encodings, the sender and receiver chips must support it at the same time. To sum up, regardless of various losses, at present, both ends need to support LDAC/LHDC at the same time to listen to lossless music with Bluetooth headsets, so if you don’t have the corresponding equipment on hand, forget about lossless music. Let me talk about a more realistic question. Even if you don’t use a Bluetooth device, for most people, lossless music is no different from lossy except that it takes up more space. Compared with lossless sound quality, lossy sound quality deletes a part of unimportant data during the compression process, and this part of the data is mainly concentrated in the high frequency part. Let’s look at the spectrogram of Hotel California at different bit rates. The horizontal axis is time and the vertical axis is frequency. Lossless sound quality, format flac, volume 37.5 MB Loss sound quality, MP3 with a bit rate of 320kbps, and a volume of 14.9 MB Loss sound quality, MP3 with 128 kbps bit rate, 6.06 MB You should be able to see that the lossy sound quality is mainly due to the lack of high-frequency data (above 17kHZ) compared to the lossless sound quality. And the lower the bit rate, the less high-frequency parts will be. However, these high frequency parts are not easy for us to hear. The reason is related to ears and equipment. Let me talk about ears first. According to the physical knowledge learned in the second grade of junior high school, the human ear can hear the range of 20 Hz-20 kHz, but in reality, few people can reach such a wide frequency band, and people can hear frequencies as they grow older. Will gradually decline. Let’s talk about equipment. When most speakers or headphones introduce parameters, they will indicate that the frequency response range is 20-20kHz, and some even exceed this range. However, it is often affected by many factors, and most devices basically can’t make sound when it is close to 20 kHz.
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