High-definition voice, also known as wideband voice, is an audio technology that delivers high-definition, natural voice quality for cellular networks, mobile phones, and wireless headsets. Compared to traditional narrowband phones, HD voice greatly improves voice quality and reduces the hearing burden. This article refers to the address: http:// All networks and devices in the communications industry chain need to support high-definition voice to reflect the advantages of this technology. As of June 2011, 20 cellular networks operated in 18 countries, as well as 33 leading mobile phone brands, have supported HD voice. High-definition voice has been introduced in GSM, WCDMA (UMTS) and LTE cellular networks by deploying adaptive multi-rate broadband (AMR-WB) speech coding. In addition, by using improved sub-band coding (mSBC) voice codec technology, wireless Bluetooth headsets are also beginning to support high-definition voice, combining hands-free calling with high voice quality. The advantages of HD voice can also be reflected in existing networks. As narrowband networks and devices transition to high-definition voice, a voice processing technology called Bandwidth Extension (BWE) can be used to simulate call quality similar to HD voice on the receiving terminal device, providing a device that does not support HD voice. A compromise solution. From narrowband to high definition voice The bandwidth of conventional telephone systems is limited to an audio frequency range of approximately 300 Hz to 3.4 kHz (Figure 1), which is commonly referred to as narrowband speech. Although the current telephone system is digital, it still inherits the same bandwidth as a traditional analog system. From a voice quality perspective, narrowband speech lacks natural speech fidelity and is often described as thin and ambiguous. Despite this, the speech discrimination of a complete sentence in the narrowband frequency range is approximately 99%. HD audio has an audio bandwidth of approximately 50 Hz to 7 kHz at a sampling frequency of 16 kHz, resulting in a clearer speech signal than narrowband speech. Although wideband speech does not significantly improve speech intelligibility, 3.4 kHz to 7 kHz outside the narrowband range increases the recognition of fricatives (eg, f, s, and th) in words. Wideband speech provides more natural and realistic speech, and has a significant improvement in subjective audio quality over narrowband speech. The low frequency of 50Hz to 300Hz extended by high-definition speech reduces the narrow-band speech sharpness, while the extended high-frequency improves the articulation. In subjective speech quality listening tests, wideband speech scored 4.5 points in the average opinion score (MOS), while narrowband speech scored 3.2 points (1 is poor quality and 5 is excellent). The improvement in broadband voice quality reduces the hearing burden and listener fatigue, especially when the listener is in a noisy environment. Mobile network operator Orange provides an audio sample on its website as an illustration of the benefits of HD voice. Another survey conducted by Orange in June 2010 further demonstrated the value of HD voice to end users: * 96% of customers are satisfied with HD voice calls; In addition, the user trial survey conducted by Ericsson and T-Mobile in 2006 also confirmed the advantages of HD voice. Among the 150 sample users, more than 70% believe that the quality of the call is better after using the high-definition voice phone, and the quality of the conversation is improved in a noisy environment. The use of high-definition voice requires a wide range of voice frequencies in all aspects of the voice communication system. The key to adopting high-definition voice technology is to cooperatively deploy AMR-WB codec in cellular networks and handheld phones. As a wideband speech coding, the effective audio bandwidth of AMR-WB is twice that of narrowband coded AMR-NB. To complete a high-definition voice call, the AMR-WB-encoded voice is cooperatively transmitted between the base station and the handset, and no voice modification or transcoding from the terminal to the terminal is performed in the process. If a high-definition voice connection is not possible, the system will instead use narrowband AMR-NB encoding. Extended voice bandwidth It can be expected that in the process of introducing high-definition voice, some links in the communication system will convert the voice into a narrowband frequency because it cannot be supported, which actually reduces the voice quality and increases the hearing burden. Artificial Bandwidth Extension (BWE) compensates for high frequency and low frequency speech content lost during transmission by adding artificially generated speech content to the narrowband speech signal at the terminal of the communication system. In this way, BWE extends the benefits of HD voice to a narrowband and transitional mixed-bandwidth voice communication system. The BWE algorithm uses a sound source filtering model that produces speech to estimate and generate speech content over a range of extended frequencies. According to the model, speech is produced by a sound source (such as a vocal cord) plus a model of the analog channel. The BWE algorithm estimates a wideband sound source model based on narrowband speech and then uses the parameters of the model to estimate its lost broadband frequency content. In practical applications, BWE is independent of source encoding and transmission path processing, so it can coexist with traditional narrowband and mixed bandwidth telephone networks. BWE is mainly used in Bluetooth headsets and hands-free devices. At the receiving terminals of these devices, the narrowband CVSD encoded speech signal is first decoded and then processed by the BWE to produce an extended bandwidth speech signal to the recipient. BWE can also be used on high-definition voice telephony networks to extend voice signals to the ultra-wideband (SWB) frequency range of 14 kHz. HD voice and sound enhancement Combining high-definition voice and sound enhancement processing methods such as Noise Suppression (NS) and Echo Cancellation (AEC) improves speech intelligibility in noisy environments and improves overall call quality. Noise suppression technology analyzes speech-doped dialogues, clears noise, and increases speech discrimination. The noise suppression algorithm estimates the noise power spectral density from a large number of frequency points and then extracts the noise from the dialogue. Compared to narrowband processing, wideband noise suppression contains more frequency point data to compress noise in the extended frequency range when calculating the noise spectrum. In addition to noise suppression, the echo cancellation processing method can eliminate the echo signal generated by the acoustic coupling between the talker and the microphone. Echo cancellation works by separating a filtered and delayed copy from the signal received by the microphone. Echo cancellation techniques are able to calculate adaptive filter coefficients in wideband speech.
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Figure 1: Bandwidth characteristics of narrowband and wideband voice
* 86% of testers said that compatible HD voice will be a selection criterion when they purchase mobile phones in the future;
* 76% of testers are willing to change their phones to get HD voice capabilities.