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

2. VOCODER TECHNOLOGY Continuous 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-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
Lower data rates = more efficient use of bandwidth
Error correction handing
Better performance in noise conditions
Lower speech quality than waveform based
Loses some “human” quality of speech

3. VOCODER TECHNOLOGY P25 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 TECHNOLOGY P25 Vocoders

5. VOCODER TECHNOLOGY Pros & Cons of P25 Vocoders
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 SAMPLES Analog vs. Digital
25kHz Channel:
Digital, IMBE / P25 Phase 1 Compliant
Direct / Simplex:
Trunk / System:
Digital, AMBE / P25 Phase 2 Compliant

7. MOTOROLA AUDIO SOLUTIONS Available Tools and Technology
Loud & Clear Audio
Adaptive Noise Cancelling
Radio Profiles
Radio can be configured with multiple operating modes.
User can select customize settings as needed.
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, ALL 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