The key index of Public Network Intercom: Speech Quality the index of speech quality measuring the speech quality of communication system mainly has two indexes: one is the MOS score of the receiving end speech; the other is the end-to-end speech delay. Time. Mos Score (Mean Opinion Score) is used to measure the "degree of restoration" of speech, including intelligibility, articulation and naturalness, after transmission through a communication system's compression coding, use A 5-point scale (5 excellent, 4 good, 3 ok, 2 bad, 1 bad) . The speech quality of the traditional PSTN telephone is generally defined as MOS 4.0 points, and the speech quality of the 2G wireless telephone is between Mos 2.5-4 points. The speech codec algorithm used in the 3G mobile telephone system can reach more than 4 points. End-to-end speech extension. Time, used to measure the real-time communication system, delay. Too much time can greatly affect the user experience of Interactive Communication. The end-to-end voice extension of a traditional PSTN telephone. Less than 16 MS; Ip Telephony Systems generally require end-to-end voice delay. Less than 300 MS; satellite phone end-to-end Voice Delay. Time greater than 500 MS. Usually when we make an IP call or a satellite call, we feel the other party is unresponsive, resulting in poor communication. Due to overage. Ip Network protocol-based Public Network Intercom System, its end-to-end delay. Time is often greater than a few hundred milliseconds, which is also an important indicator of user experience. The main factors that affect the quality of public network intercom are divided into two parts, one is the terminal hardware, including microphone, speaker, Cavity Structure and audio circuit The other part is the platform system design factors, including speech codec Algorithm, audio enhancement Algorithm, transmission strategy and server processing mechanism. This article mainly introduces several factors of the public network intercom platform to the user's sound quality experience. Speech codec Algorithm (also known as Vocoder) : is the public network to determine the radio platform can provide the basic factor of speech quality. In other words, if the platform used by the speech codec Algorithm can provide poor speech quality, terminal hardware audio design can not fundamentally improve the quality of speech. The existing public network intercom platform mainly uses three types of speech codec, one is the early platform supporting 2g CDMA network, using EVRC variable-rate vocoder half-rate (4Kbps) coding, its sound quality is poor, Mos score only about 3.0 points; The second class is based on supporting 3G mobile network, using 3GPP avariable-rate vocoder (4.75 kbps-12.2 kbps) , its full-rate encoding and decoding sound quality can reach above Mos 4.0 points, the third class is derived from VoIP system, using ITU G. 72X speech coding standard, the encoding and decoding algorithm can be selected according to terminal capability matching. ★ speech enhancement: mainly including environmental noise suppression, adaptive Acoustic Echo cancellation, automatic gain control, adaptive equalization and other algorithms. The application of speech enhancement technology has a great impact on the user's experience of sound quality. Transmission Strategy: The Public Network Intercom System based on wireless IP network transmission must face the influence of network transmission factors such as packet loss, jitter and disorder on the sound quality, therefore, it is necessary to design an effective transmission strategy to counter the adverse effects of these network features on speech quality. Therefore, for the Public Intercom Platform under the OTT system, it is not difficult to realize the basic functions of the Public Intercom Service. In a good network environment, the "demonstration" effect may also perform well, but there are all kinds of sound quality problems when users actually use it. Therefore, to the Public Network Intercom Platform, it is difficult to provide a good user experience in different network environments. Can the voice quality of 4G Public Network Intercom be greatly improved? Using 2 G Network Public Intercom users already familiar with 2 g public intercom sound quality, voice delay. When the big problem, in the 2G public network interphone to 4G public network interphone transition process, users will inevitably ask, 4g network bandwidth, transmission speed, voice quality can also be greatly improved? The answer is "not sure" , 4g public network intercom can greatly improve the voice quality, but it is not 4g terminal can improve the voice quality, but depends on the platform system design can effectively use the bandwidth advantage of 4G network. As mentioned above, the fundamental factor in the sound quality of public network interphone systems is what kind of speech CODEC is used, if the platform can only support low bit rate and low quality speech CODEC, it doesn't adjust the transmission control strategy according to the advantage of 4G network, and can't make full use of the bandwidth advantage of 4G network. 4G Public Network interphone has no name in vain, and can not improve the sound quality experience for users. 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