DRC - Dynamic Range Compression
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About Dynamic Range Compression and Automatic Gain Control
Mobile voice communication is often conducted in noisy environments. The simplest way to improve speech intelligibility in a noisy environment is to increase the sound volume. Unfortunately, in many practical situations, the output sound level produced by a communication device is limited due to the amplifier, loudspeaker or power consumptions reasons.
The question arises: Can we modify the sound being reproduced by the speaker so that it becomes more understandable in noise, while preserving its level?
The answer is: Yes
The simplest way of doing that is to compress the signal. Compression reduces the dynamic range of a signal by lowering (compressing) amplitudes of strong speech segments while preserving amplitudes of weaker segments. As a result, weak signals are better heard in noisy situations while strong signals do not overload the power amplifier, loudspeaker or user’s ears. In a paper (link to scientific paper below) published in the Journal of Audio Engineering Society was shown that compression is a hidden weapon of commercial advertising, allowing increase in perceptual loudness while preserving all "objective" measured sound levels.
Dynamic Range Compression (DRC) is a standard part of Alango Voice Communication Package (VCP). It is performed on the microphone channel in the basic VCP version and on both microphone and speaker channels in the advanced VCP version.
Alango offers alternative solution by exploiting its fast and reliable AGC algorithm. Instead of compressing user’s voice when it is strong, Alango AGC technology digitally increases microphone channel gain when user’s voice is weak. When no user’s voice is detected by the Alango robust voice activity detector, no gain change is performed. In noisy places people tend to speak loudly which automatically sets the microphone channel gain to a small value thus reducing ambient noises while keeping user’s voice at the optimal level. Alternatively, in quiet environment people speak softly so their voice are amplified by the algorithm but, no ambient noise present anyway. In practice, a combination of AGC algorithm with a mild DRC algorithm (both from Alango) gives the best results.
In the speakerphone mode the problem is slightly different. The relative noise level in the input signal may be large but the speed of voice level variations is generally lower. Again a combination of AGC and DRC algorithms gives excellent results with all people being heard well irrespective of the distance to the mobile phone (speakerphone).
DRC and other technologies
Although it can be used standalone, Dynamic Range Compression technology is also integrated with other Alango technologies into one Voice Communication Package (VCP). The package also includes acoustic echo cancellation, stationary and transient noise suppression, speech enhancement, (optional) adaptive dual microphone, automatic volume and equalization comtrol, and several others.
More detailed technical information and examples are available upon request.
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