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Advanced intercom systems

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Technologies and solutions for advanced intercom systems

Alango provides an efficient, cost effective add-on solution to introduce acoustic echo cancellation and other useful signal processing into intercom systems. Different types of intercom systems are supported such as door intercom systems, counter intercom systems, industrial intercom systems and others. Alango solution is based on CSR BlueCore 5 Multimedia (BC05MM) chip that combines a powerful, 64MIPS, 24bit DSP, Microcontroller and stereo audio CODEC. While it is possible to create a Bluetooth intercom system, for most intercom systems the Bluetooth radio on BC05MM chip is disabled.

BC05MM chip is designed for small form-factor, mass-market applications (e.g. Bluetooth headsets). As such it may be not convenient to handle in relatively low volume intercom products. The recommended solution is to use a BC05MM based module that is much easier to integrate. An example of such Voice Processing Module (VPM) is shown in the picture below. There are many vendors providing low cost, BC05MM based modules with similar parameters and price.

In the signal chain VPM is placed at the front of an intercom system. From one end it is connected to a microphone and power amplifier and from another end to the rest of the intercom system providing signal transmission between the voice terminals as well as its control functionality. The picture below illustrates a typical VPM location inside an intercom system terminal.

Voice Processing Module integrates Alango Voice Communication Package (VCP) of software technologies performing digital signal processing of its input signals. The figure below illustrates VCP processing blocks on the transmit (Tx) and receive (Rx) paths. Analog-to-digital and digital-to-analog converters are omitted for simplicity.

The following processing tasks are currently supported by VCP integrated into VPM firmware:

  • Acoustic Echo Cancellation (AEC): Cancels acoustic echo caused by the speaker and microphone proximity
  • Noise Suppression (NS): Reduces stationary and transient noises improving the quality of voice signal
  • Equalizer (EQ): Performs frequency equalization of Rx, Tx signals improving their perceptual quality; operates in 32 frequency bands
  • Noise Gate (NG): removes low level electronics and other annoying noises during idles periods
  • Automatic Gain Control (AGC) and Dynamic Range Compressor (DRC): reduce variations in a signal level
  • Noise Dependent Volume Control (NDVC): changes the loudspeaker volume according to the ambient noise. Automatically solves the dilemma of “too loud in quiet vs. too soft in noise”.
  • Double Talk Gain Control (DTGC): improves double talk performance slightly reducing Rx gain when near talk is detected.

Each of VCP processing blocks can be enabled, disabled or configured according to specific conditions of use, acoustic design or individual customer preferences. For configuration or acoustic tuning task VPM is connected to PC via a special “debugger” card. Alango provides VCP Configurator which a special visual PC application. VCP Configurator allows changing the parameters “on the fly” making acoustic tuning an interactive process.

The following parameters are configurable:

  • input/output analog and digital gains
  • echo cancellation parameters (echo tail length, speaker distortion level and others)
  • noise suppression parameters (SNR improvement, noise adaptation time, sensitivity and others)
  • automatic gain control parameters (maximal gains, reaction time)
  • other parameters

When add-on hardware solution is expensive, Alango licenses software solutions on various processing platforms.

Please, contact us for more technical information, pricing and other questions.

 

 

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