How HD Voice Technology is Implemented in Blueto
HD Voice, also known as wideband voice, is an audio technology that transmits high definition, natural voice quality to cellular networks, cell phones and wireless headsets. Compared to traditional narrowband telephony, HD Voice largely improves voice quality and reduces the listening burden.Even though your china headphone will come with some battery charge, it’s advisable to fully charge them before first use. Connect them to a suitable USB power source using the USB lead provided and leave charging for around 2.5 hours or until the red charging LED goes out.All networks and devices in the communications chain need to support HD Voice in order to realize the benefits of this technology. As of June 2011, 20 cellular networks operating in 18 countries, as well as 33 leading handset brands, support HD Voice. HD Voice has been introduced into GSM, WCDMA (UMTS) and LTE cellular networks through the deployment of Adaptive Multi-Rate Wideband (AMR-WB) voice coding. In addition, wireless Bluetooth headsets are beginning to support HD voice through the use of improved subband coding (mSBC) voice codecs that combine hands-free calling with high voice quality.The benefits of HD voice can also be seen in existing networks. As narrowband networks and devices transition to HD voice, a voice processing technique called bandwidth extension (BWE) can be used to emulate HD-like call quality on the receiving end of the device, providing a compromise solution for devices that do not support HD voice.From narrowband to HD voice: The bandwidth of traditional telephone systems is limited to an audio frequency range of approximately 300 Hz to 3.4 kHz (Figure 1), a range commonly referred to as narrowband voice. Even though today's telephone systems are digital, they still inherit the same bandwidth as traditional analog systems. From a speech quality perspective, narrowband speech lacks natural speech fidelity and is often described as thin and muffled. Nevertheless, the speech recognition rate of the complete corpus is about 99% in the narrowband frequency range.HD speech has an audio bandwidth of about 50 to 7 kHz and a sampling frequency of 16 kHz, resulting in a clearer speech signal compared to narrowband speech. While wideband speech does not significantly improve speech intelligibility, the 3.4 kHz to 7 kHz outside the narrowband range improves the recognition of fricatives in words such as f, s and th. Wideband speech provides more natural and realistic speech, with a significant improvement in subjective audio quality over narrowband speech. The extended low frequencies of 50 Hz to 300 Hz in HD speech reduce the sharp and thin characteristics of narrowband speech, while the extended high frequencies improve articulation clarity.The use of HD voice requires that all links in the voice communications system support a broadband voice frequency range. The key to adopting HD voice technology is the cooperative deployment of AMR-WB codecs in cellular networks and handheld phones. As a wideband voice codec, AMR-WB has twice the effective audio bandwidth of the narrowband codec AMR-NB. To complete an HD voice call, voice encoded with AMR-WB is transmitted collaboratively between the base station and the handheld phone, with no voice modification or conversion coding from terminal to terminal in the process. If an HD voice connection is not possible, the system will use narrowband AMR-NB encoding instead.
