ACC is a technology provided by Dolby Laboratories for the music community and is a high compression ratio encoding algorithm. In actual experience, it is believed that under the same bit rate, ACC has a better listening experience than MP3, and Apple has a lot of audio on ACC.
Therefore, the audio transmission format of the current iPhone is also in the acc format, and the bit rate is equivalent to SBC, but the sense of hearing is said to be better than SBC. Because no serious comparison has been done, I think it is slightly better than SBC.
AAC claims to "can accommodate a maximum of 48 channels of audio tracks with a sampling rate of 96 KHz, and can provide 5.1 channel music programs with a quality equivalent to ITU-R broadcasting at a data rate of 320 Kbps." Compared with MP3, its sound quality is better, and it can save about 30% of storage space and bandwidth. It is a technology developed following the MPEG-2 specifications. Panasonic's mp3 products use this encoding method, of course, also compatible with mp3 format. It can be said that aac is a very easy-to-use audio format. The 128acps aac is enough to compete with the 224kbps mp3, but the space is almost half, but Spatially and structurally, the style after encoding aac and mp3 is not the same.
There are three main extensions for AAC encoding:
.AAC-Use the MPEG-2 Audio Transport Stream (ADTS, see MPEG-2) container, which is different from the MP4 / M4A format using the MPEG-4 container, which belongs to the traditional AAC encoding (FAAC default packaging, but FAAC can also output MPEG -4 packaged AAC)
.MP4-AAC encoding using 3GPP Media Release 6 Basic (3gp6, see 3GP) which is a simplified version of MPEG-4 Part 14 (Part 14) (Nero AAC encoder can only output MPEG-4 encapsulated AAC) ;
.M4A-An extension used by Apple to distinguish between audio-only MP4 files and video-containing MP4 files, Apple iTunes uses the name ".M4A" for audio-only MP4 files. The essence of M4A is the same as audio MP4, so audio MP4 files can also be directly changed to M4A.
SBC (Sub-band coding)The earliest format should be SBC, which is a mandatory encoding format specified 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. The specific parameters of the bit rate of the SBC code during transmission were not found. According to the information given on the sony official website, it is: 328Kbps, 44.1KHZ.
This code rate is actually similar to high-quality MP3. But because the Bluetooth transmission intermediate device needs transcoding, taking MP3 files as an example, the transcoding process is MP3-》 PCM-》 SBC-》 PCM, and every transcoding will lose details, resulting in SBC's hearing feeling will be better than the original MP3 To be worse.
First, the input signal is divided into several sub-band signals in different frequency bands through a set of band-pass filters, and then these signals are converted into baseband signals through frequency shift, and then they are sampled separately. The sampled signal is quantized, coded, and synthesized into a total code stream and sent to the receiving end. At the receiving end, the code stream is first divided into sub-band code streams corresponding to the original sub-band signals, and then decoded, the spectrum is moved to the original position, and finally the band-pass filtered and added signal is reconstructed.
Advantages: You can take advantage of the different sensitivity of the human ear (or human eye) to different frequency signals. Rough quantization can be used in parts that are not sensitive to human hearing (or vision), and finer quantization can be used in sensitive parts. Get better subjective hearing (visual) effects. For example, the pitch and formants of speech are mainly concentrated in the low frequency band, so more bits can be assigned to represent their samples; while the high frequency bands with friction sounds and similar friction noise can be assigned fewer bits, so that they can be fully compressed Voice data.
The quantization noise of each sub-band is bound in this sub-band, so that the signal in the frequency band with smaller energy can be prevented from being masked by the quantization noise in other frequency bands.
The specific implementation of the filter cannot be an ideal bandpass, and its amplitude effect inevitably has a limited roll-off. Therefore, when subbands are divided, there can only be overlap between subbands or a certain gap between subbands. The former will produce aliasing distortion if it is sampled at the Ness frequency, while the latter will cause the original part of the frequency band to be filtered and lost, and the reconstructed signal will be distorted. The solutions to this problem include orthogonal mirror filtering and time-domain aliasing elimination.
APTXAPTX is CSR's patented coding algorithm. After being acquired by Qualcomm, APTX has been widely promoted in Android phones.
According to the official website, aptX is divided into three types: aptX, aptX HD and aptX Low Latency. According to the name, it can be considered as traditional aptX, high-quality aptX (estimated to increase the code rate) and low time delay aptX (when watching video and playing Time delay is very important in CS).
The Qualcomm® aptX ™ audio coding algorithm originated in the late 1980s at Queen's University Belfast. This innovaTIve work was focused on bit rate reducTIon and achieved significant bit rate efficiencies while preserving audio quality.
aptX has been the best kept secret of the professional audio industry, used by major public broadcasters and film studios around the world. Now available on leading consumer devices, aptX enables music lovers to enjoy the rich listening experience that aptX delivers.
Qualcomm probably means that aptX belongs to my family, and then the audio coding algorithm developed by Queen's University in the 1980s. This algorithm has high bit rate efficiency while maintaining high audio quality. As a professional wireless audio transmission solution, aptX is used in public broadcasting and movie sound, and now it is finally going to be placed in consumer products.
Therefore, the transmission rate of aptX is actually not high. It may be similar to the previous two, but thanks to efficient coding, the details of sound retention are more. Achieve CD-level listening experience.
Apt-X is a digital audio compression algorithm based on sub-band ADPCM (SB-ADPCM) technology. The original algorithm was proposed by Dr. Stephen Smyth in the 1980s. Developed by Audio Processing Technology (now merged with CSR) and named apt-X. Originally used in the field of professional audio and broadcasting. In recent years, in the field of Bluetooth wireless audio transmission, apt-x has a tendency to replace SBC (Sub-band Coding) due to its advantages of low latency, good fault tolerance, and high sound quality. At present, the apt-x family has aptX Bluetooth, aptX Enhanced, aptX Live (launched in 2007), aptX Lossless (launched in 2009). apt-X has the following characteristics:
Desired bandwidth: 10Hz to 22.5 kHz, 56kbit / s to 576 kbit / s (16 bit 7.5 kHz mono to 24-bit, 22.5kHz stereo)
The use of Apt-X is mainly focused on Bluetooth headsets and Bluetooth speakers. Both its terminal and Bluetooth headset speakers must support Apt-X to play its functions. There is a certain delay in Bluetooth audio transmission. The biggest feeling is that the audio and video delay can be minimized.
LDACNow it ’s Dafa ’s turn. Dafa has simply and rudely improved the channel. On devices that support LDAC, the communication bit rate of Bluetooth is close to 1M.
LDAC can transmit about 3 times the data of ordinary Bluetooth * 1 (at a transmission speed of up to 990kbps * 2), allowing you to listen to Hi-Res Audio * 3 music wirelessly, you can listen to Hi-Res Audio Sound quality.
With such a high transmission speed, it is possible to transmit lossless music. Of course, the transmission format of this near-private protocol also leads to only a small number of compatible devices. But there is no doubt that LDAC has greatly improved the transmission rate, making the transmitted audio quality higher, and the listening sense is naturally the best.
The next issue will cover the current situation of various Bluetooth audio SOC manufacturers and support for various formats. Then the live development and actual development of CSR8670 and CSRA64215 will be broadcast live.
LDAC is a wireless audio coding technology developed by Sony. It was first unveiled at the CES Consumer Electronics Show in 2015. At the time, Sony stated that LDAC technology was three times more efficient than standard Bluetooth encoding and compression systems. In this way, those high-resolution audio files will not be excessively compressed when wirelessly transmitted, so that the sound quality will be greatly lost.
The reason why Sony's decision is quite concerned is that LDAC technology was almost "Sony only" in the past, only applied to its own mobile phones, players, headphones, Bluetooth speakers. Because LDAC technology relies on the simultaneous support of audio sources and speaker systems, this makes the technology an exclusive highlight of Sony equipment. Now, as long as it is a mobile phone with Android O installed, it can use LDAC to allow users to enjoy wireless high-definition music on a playback system that supports the technology.
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