VOCODER TECHNOLOGYVOCODER TECHNOLOGY

OCTOBER 23-24, 2012OCTOBER 23-24, 2012

David Chambers | Sr. Staff EngineerProduct Engineering, Motorola SolutionsDavid Chambers | Sr. Staff EngineerProduct Engineering, Motorola Solutions

VOCODER TECHNOLOGYContinuous vs. Model BasedVocoder: 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-sample basis• 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 PAGE 2

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 interoperabilityCompliance

• 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

VOCODER TECHNOLOGYP25 Vocoders

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VOCODER TECHNOLOGYP25 Vocoders

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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

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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:

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Radio can be configured with multiple operating modes.

User can select customize settings as needed.

MOTOROLA AUDIO SOLUTIONSAvailable Tools and Technology

Adaptive Noise Cancelling

Dual-microphones adapt to the direction of background noise

Optimized for both digital and analog modes

Loud & Clear Audio

Class D amplifier for increased loudness and clarity

No Compromises in Audio Quality DesignNo Compromises in Audio Quality Design

Radio Profiles

CONCLUSIONDigital Audio Quality is Limited by Vocoder Technology

• To be P25 compliant, ALLALL radio 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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