PCM encoding (original Digital Audio Signal Stream)
Type: Audio
Maker: ITU-T
Required bandwidth: 1411.2 kbps
Feature: sound source information is complete, but redundant
Advantages: sound source information is fully saved and sound quality is good
Disadvantages: Large Information volume, large Redundancy
Application: VoIP
Royalty: free
Note: in computer applications, PCM encoding can reach the highest fidelity level, which is widely used for material storage and music appreciation. CD, DVD, and common wav files are all used. Therefore, PCM is about lossless encoding, because PCM represents the best fidelity level in digital audio, does not mean that PCM can ensure absolute fidelity of the signal, PCM can only achieve the maximum infinite proximity. It is easy to calculate the bit rate of a pcm audio stream. The sampling rate value × the sample size Value × the number of audio channels bps. A pcm-encoded WAV file with a sampling rate of 44.1 kHz and a sampling size of 16 bit. The data rate is 44.1k × 16 × 2 = 1411.2.
Kbps. Our common audio CD adopts PCM encoding. The capacity of a CD can only accommodate 72 minutes of music information.
WMA (Windows Media Audio)
Type: Audio
Developer: Microsoft
Required bandwidth: 320 ~ 112 kbps (compressed 10 ~ 12 times)
Feature: When the bitrate is less than K, WMA performs the most well in almost all lossy encoding formats at the same level, but it seems that the K is a watermark of WMA. When the bitrate is increased, there won't be too many changes in sound quality.
Advantage: When the bitrate is less than K, the WMA is the best and the encoded audio file is very small.
Disadvantage: When the bitrate is greater than K, the loss of WMA sound quality is too high. The WMA standard is not open to Microsoft.
Application: VoIP
Royalty: charged by instance
Note: The full name of WMA is Windows Media Audio, which is a new audio format launched by Microsoft in the same name as the MP3 format. Since WMA outperforms MP3 in terms of compression ratio and sound quality, it is far better than RA (Real Audio) in that it can produce better sound quality even at a low sampling frequency, in addition, WMA has the powerful backing of Microsoft's Windows Media Player, So it won a review once it was launched.
PCMU (g.711u)
Type: Audio
Maker: ITU-T
Required bandwidth: 64 Kbps (90.4)
Features: Both PCMU and PCMA provide better speech quality, but they occupy a high bandwidth and require 64 Kbps.
Advantage: Excellent speech quality
Disadvantage: the occupied bandwidth is high.
Application: VoIP
Royalty: free
Note: Both PCMU and PCMA can achieve CD sound quality, but they consume the most bandwidth (64 Kbps ). If the network bandwidth is relatively low, you can use low bit rate encoding methods, such as g.723 or g.729.
The code method can also achieve the sound quality of traditional long-distance calls, but requires a small amount of bandwidth (g723 requires 5.3/6.3 kbps, g729 requires 8 kbps ). If the bandwidth is sufficient and the voice quality needs to be better, PCMU and PCMA can be used, and even the broadband encoding method g722 (64 Kbps) can be used, which can provide high-fidelity sound quality.
PCMA (g.711a)
Type: Audio
Maker: ITU-T
Required bandwidth: 64 Kbps (90.4)
Features: Both PCMU and PCMA provide better speech quality, but they occupy a high bandwidth and require 64 Kbps.
Advantage: Excellent speech quality
Disadvantage: the occupied bandwidth is high.
Application: VoIP
Royalty: free
