Voice Communication Package (VCP) combines a set of front-end digital speech enhancement technologies enabling high quality voice communication in mobile and stationary environments:
- Echo Cancellation (Acoustic and Line)
- Stationary and Transient Noise Suppression
- Automatic Gain Control
- Dynamic Range Compressor/Limiter
- Automatic Volume and Equalization control (amplifies and equalizes speaker signal according to ambient noise)
- Voice Activity Detector
- 32 band static and dynamic equalizer
- Optional Adaptive Dual Microphone
All technologies are built for low power, low resources applications sharing the same, 32 bands frequency decomposition scheme allowing very efficient implementations on both DSP and RISK platforms. VCP speakerphone acoustic echo cancellation (64ms echo tail), noise suppression, automatic gain control and all other components altogether take about 28MHz of processor clock on ARM9 and about 32MHz on ARM7. These numbers can be further reduced for specific applications.
VCP technologies are scalable for different applications ranging from low cost voice terminals and mobile phones to high-end audio conferencing systems. Alango proprietary subband adaptive filters converge in single and double talk following possible fast changes in acoustic conditions (e.g. when the microphone or speaker positions are changed). Alango subband residual echo suppressor continuously estimates current acoustic conditions in each frequency subband automatically adapting its parameters to provide the best performance. The technology directly takes into account loudspeaker distortions achieving optimal duplex communication with each acoustic design. Alango acoustic echo cancellation technology is compliant with VDA specifications for hands-free in-vehicle voice terminals (class 1-2a).
Alango Noise Suppression technology is characterized by very fast adaptation time to variations in noise level and spectrum allowing suppression of fast changing, transient noises (e.g. passing cars). The algorithm is also characterized by low voice distortions and lack of other artifacts such as musical noise.
Automatic Volume & eQualization control (AVQ) technology monitors ambient noise level and spectrum on the microphone used in a voice communication system and automatically amplifies/equalizes the loudspeaker signal accordingly providing equal perceptual loudness in varying conditions.
32-band equalizer allows straightforward shaping/correction of microphone and speaker frequency responses for clear, intelligible sound and compliance with telecommunication standards.
VCP has a convenient API easily configurable for different applications and modes of device operation. The mechanism of "profiles" allows easy change of processing parameters for cases when acoustic conditions are changed (e.g. switching between handset and hands-free profile in a mobile phone).