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VOCODER TECHNOLOGY

OCTOBER 23-24, 2012. VOCODER TECHNOLOGY. David Chambers | Sr. Staff Engineer Product Engineering, Motorola Solutions. VOCODER TECHNOLOGY Continuous vs. Model Based. Vocoder: Voice Encoder

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VOCODER TECHNOLOGY

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  1. OCTOBER 23-24, 2012 VOCODER TECHNOLOGY David Chambers | Sr. Staff EngineerProduct Engineering, Motorola Solutions

  2. VOCODER TECHNOLOGYContinuous vs. Model Based • Vocoder: Voice Encoder • Objective: Synthesize a speech signal to contain the same perceptual information as the original signal • Continuous “Waveform” Based • Objective: Reproduce at the decoder the original speech samples on a sample-by-samplebasis • Advantages • Capable of very good audio quality • Modest complexity • Disadvantages • Quantization errors for lower data rates requires relatively high data rates (minimum 16,000 b/s) • Not good in speech + noise conditions • Model Based • Objective: Create a model that accurately represents speech (an estimation of how speech works) • P25 vocoders • Advantages • Lower data rates = more efficient use of bandwidth • Error correction handing • Better performance in noise conditions • Disadvantages • Lower speech quality than waveform based • Loses some “human” quality of speech

  3. VOCODER TECHNOLOGYP25 Vocoders • Background • Project 25 or APCO-25 (Association of Public-Safety Communications Officials) • A collaborative project by public safety agencies in North America to ensure two-way radio interoperability • Compliance • Suite of Standards for Digital Radio Communication Systems • Specifies 8 open interfaces between the various components of a radio system • P25 Standards use Vocoders • Improved Multi-Band Excitation (IMBE) vocoders for Phase 1 • Advanced Multi-Band Excitation (AMBE) vocoders for Phase 1 & 2 • ALL vocoders supplied by one company, DVSI • Specifications • FDMA “Full Rate” • 7,200 b/s with Forward Error Correction • P25 Phase 1 Compliance • TDMA “Half Rate” • 3,600 b/s with Forward Error Correction • P25 Phase 2 Compliance

  4. VOCODER TECHNOLOGYP25 Vocoders

  5. VOCODER TECHNOLOGYPros & Cons of P25 Vocoders • Pros • Lower data rates = more efficient use of bandwidth • Forward Error Correction • Better performance in noise conditions • Robust speech model • Cons • Lower speech quality than waveform based vocoders with much higher data rates • Loses some “human” quality of speech

  6. AUDIO SAMPLESAnalog vs. Digital • Analog • 25kHz Channel: • Digital, IMBE / P25 Phase 1 Compliant • Direct / Simplex: • Trunk / System: • Digital, AMBE / P25 Phase 2 Compliant • Direct / Simplex: • Trunk / System:

  7. Radio can be configured with multiple operating modes. • User can select customize settings as needed. MOTOROLA AUDIO SOLUTIONSAvailable Tools and Technology Loud & Clear Audio Radio Profiles Adaptive Noise Cancelling • Dual-microphones adapt to the direction of background noise • Optimized for both digital and analog modes • Class D amplifier for increased loudness and clarity No Compromises in Audio Quality Design

  8. CONCLUSION • Digital Audio Quality is Limited by Vocoder Technology • To be P25 compliant, ALLradio manufacturers must use the same vocoder supplied by DVSI • P25 vocoders (IMBE / AMBE) use Speech Models • Lower data rates, better noise performance, robust but some loss of “human” quality of speech • Motorola Technology • Audio enhancements to help improve digital audio quality • Advanced noise suppression • Customization of audio using Radio Profiles • High quality receiver components

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