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A full-duplex speakerphone or intercom device digitizes the signal coming out of its speaker. It then edits this info out of the signal it’s transmitting using a built-in digital processor. This eliminates echo effect and more importantly, does away with the on-off mic/speaker dilemma. Full-duplex devices do all of this virtually instantaneously.

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Full-duplex conversation, where both transmit and receive channels are active simultaneously, is the conversation. Full duplex for hands-free communications is achieved using Echo Cancellation. Echo Cancellation reduces overall loop gain and the acoustic coupling between speaker and microphone. This coupling reduction prevents the annoying effect of hearing one’s own delayed speech, which is worsened when there is delay in the system, such as vocoder delay.

Half-duplex devices let you send and receive, but only one-way at a time. If you’ve ever used a walkie-talkie, then you know what half-duplex conversations sound like. You have to push the TALK button to send your message. But as long as you are holding the TALK key, you can’t hear what anyone else is saying. You must release the button to receive.

This software can be combined with VOCAL’s VoIPTelephonyVoice CodecData Modem, and/or Fax Modem modules.

The line interface may be an analog front end (codec and DAA) or a digital interface such as T1/E1, Switched 56, and ISDN.


  • Full Duplex
  • Lower MIPS Half Duplex version available
  • Acoustical Echo Cancellation (AEC)
  • Line Echo Cancellation (G.168 compliant)
  • Automatic Gain Controls
  • Frequency response (+/-3 dB referenced to 1kHz) of 300 Hz to 3.4 kHz
  • 2048 cefficients
  • Train on voice (no training tones)
  • Convergence Time of 300 ms maximum
  • Acoustic Tail Length of up to 256 ms


  • Seamlessly integrates into VOCAL’s microkernel
  • Can be combined with North American and International telephony platforms. These platforms feature voice activity detection, international call progress, caller ID
  • Can be combined with data modulations and protocols (modulations through V.34 Annex A and V.42/V.42bis and MNP 1-5 data protocols)
  • Can be combined with facsimile modulations and protocols (modulations through V.17 and T.4/T.30 facsimile protocols)
  • Can be combined with data, facsimile and voice command sets
  • Can be combined with speech coders including DSVD G.729 Annex A

More Information

VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Amherst New York 14228
Phone: +1-716-688-4675
Fax: +1-716-639-0713