Introduction —
Acoustic echo cancellation —
Noise reduction and speech reconstruction —
Multi-channel support —
Automatic gain control —
Equalization —
Wind buffet suppression —
Intelligibility enhancement —
Noise dependent receive gain —
Bandwidth extension —
Wideband support —
Appendix: Decision checklists
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Introduction
As mobile phones evolve to take advantage of emerging LTE, 4G networks, the performance demands on in-vehicle hands-free systems will only increase. Where yesterday almost any more or less comprehensible hands-free communication was ...
Acoustic echo cancellation
Acoustic echo cancellation should handle double-talk and be stable, even under the harsh acoustic environment of the vehicle cabin and with the less than ideal transmission of mobile networks. In an in-vehicle hands-free call ...
Noise reduction and speech reconstruction
Noise reduction must not impact the quality of speech, but improve the signal-to-noise ratio and attenuate the effects of mobile network gating.
Automobiles are subject ...
Multi-channel support
Multiple input channels must be available so that the vehicle manufacturer can offer different microphone arrays and configurations, as well as block some inputs during speech recognition activities.
In-vehicle hands-free systems are often required ...
Automatic gain control
Gain control should accurately differentiate between voice and other sounds, such as wind buffeting, and it should use a soft look-ahead limiter to maintain a consistent voice level both when sending and receiving.
A hands-free system mus ...
Equalization
Equalization should be simple and handle both high- and low-noise conditions.
An in-vehicle hands-free system must accommodate significant differences in send and receive frequency response in order to accommodate differences i ...
Wind buffet suppression
An efficient algorithm for handling wind buffeting is a key component of any hands-free system.
Automobile interiors are filled with constantly changing winds and turbulence: HVACIntelligibility enhancement ...
Intelligibility enhancement
Intelligibility enhancement techniques must complement noise reduction.
In hands-free communication, lower frequency consonants (e.g. /p/, /t/ /k/, etc.) are often masked by the noise in the vehicle. Fortunately, because noise is predominantly ...
Noise dependent receive gain
Noise dependent receive gain should be smooth, with parametric control of change rates, and it should use algorithms that make minimal assumptions about the acoustic environment.
To help compensate for loudness masking ...
Bandwidth extension
Improvements to speech through bandwidth extension is difficult to accomplish, but is important for today’s dominant narrowband communications.
Improving the intelligibility of far-end speech is especially valuable in a noisy ...
Wideband support
Mobile networks are beginning to adopt wideband communications, which will soon render obsolete any hands-free system that does not support this technology.
Cellular networks in Europe and North America are beginning to support bandwidths ...
Appendix: Decision checklists
The checklist below follows the same general organization as the whitepaper, plus other items that will affect the success of a project. It may be
