AMBE+2 compatible DMR (ETSI TS 102 361) / dPMR (ETSI TS 102 658) standard vocoder for 2450 bps (without FEC). 

For Digital Mobile Radio (DMR), digital Private Mobile Radio (dPMR) and other markets.

 Technology Features. The DMR Vocoder was implemented as a software in exact accordance with the following documents:

  • TIA/EIA-102.BABA Vocoder Description (December 2003)

  • TIA-102.BABA-1 APCO Project 25 Half-Rate Vocoder Addendum (April 2009)

To improve speech quality and other technical characteristics of the vocoder, IMBE-method of analysis and synthesis, which is described in the documents mentioned above, was replaced by AMBE+ method, that is described in some patents of the DVSI company.
Moreover, AMBE+ method was modified by DSPINI's experts in part of more accurate estimation of the MBE-parameters, more accurate synthesis of speech as well as to provide correct processing of the non-speech signals and to provide additional functionalities.

This software completely satisfies requirements of the standards and provides full compatibility and interoperability with AMBE+2 vocoder from DVSI, as for transmission of speech, as well as for tone signals.
It was carefully tested using DVSI's AMBE-3000 HDK at Rate #33.

 Speech Quality. Here is a comparison with DVSI's AMBE+2 and TWELP vocoders. TWELP 2400 bps vocoder, DVSI's AMBE+2 2450 bps vocoder (DVSI's AMBE-3000 chip, rate 33) and DSPINI's DMR 2450 bps vocoder were tested, using ITU-T P.50 speech base for 20 different languages. ITU-T P.862 utility was used for estimation of the speech quality in PESQ terms:

 
DSPINI's implementation of the DMR vocoder provides in practice the same speech quality like DVSI's AMBE+2 vocoder. TWELP vocoder provides much better speech quality in comparison with both MBE-based vocoders. Exact numbers are presented in the table below.
LanguageTWELP 2400AMBE+2 2450DMR 2450
American 3.247 3.085 3.109
Arabic 3.157 3.014 3.034
British 3.106 3.072 3.068
Chinese 3.192 2.979 2.969
Danish 3.184 2.941 3.030
Dutch 3.004 2.900 2.909
Finnich 2.970 2.867 2.826
French 3.135 3.117 3.084
German 3.121 2.971 3.030
Greek 3.140 2.992 2.980
Hindi 3.152 3.097 3.040
Hungarian 3.192 3.037 3.019
Italian 3.325 3.155 3.148
Japanese 3.261 3.151 3.158
Norwegian 3.173 2.964 2.991
Polish 3.178 2.944 2.969
Portuguese 3.191 3.175 3.087
Russian 3.076 2.980 3.016
Spanish 3.201 3.099 3.062
Swedish 3.203 3.053 3.037
Average3.1603.0303.030

An averaged quality of the DMR and AMBE+2 vocoders are exactly the same.
Superiority of the TWELP 2400 bps vocoder is on average 0.13 PESQ.


Speech Samples (WAV-files). A few independent experts listened DMR 2450 bps vocoder in comparison with AMBE+2 2450 bps vocoder and TWELP 2400 bps vocoder, using method of preferences.
A majority of experts haven't found a difference between DMR and AMBE+2 vocoders, but preferred TWELP to both DMR vocoders, having noted much more natural human-sound of voice in the TWELP vocoder.
You can play and listen short samples of the source speech as well as the speech processed by these vocoders for any of 20 languages, using links in the table below.
Also, you can download full set of the P.50 samples as zip-files for all languages simultaneously, using the links in the "Downloads" para in a bottom of the page.

LanguageSource speechAMBE+2 2450 bpsDMR 2450 bpsTWELP 2400 bps
American
Arabic
British
Chinese
Danish
Dutch
Finnich
French
German
Greek
Hindi
Hungarian
Italian
Japanese
Norwegian
Polish
Portuguese
Russian
Spanish
Swedish

 Quality Of The Non-speech Signals. Unfortunately, MBE-based vocoders cannot process non-speech signals, including police, ambulance, fire sirens, etc., correctly. In contrast, TWELP vocoders provide high quality of non-speech signals. This feature in conjunction with high quality natural human-sound of voice makes TWELP vocoders well suitable for replacement of analog radio by digital radio and also for other applications where high quality transmitting of non-speech signals is relevant along with high quality transmitting of speech signals.

Source typeSource signalDMR 2450 bpsTWELP 2400 bps
Siren only
With voice

 Robustness To Acoustic Noise. In contrast to other LBR vocoders, TWELP vocoders are well robust to acoustic noise thanks to robust reliable method of pitch estimation and other features of TWELP technology.

Moreover, vocoder includes in-built Noise Cancellation—Speech Enhancement (NCSE) functionality that improves speech quality in noisy acoustic environment.

NCSE ModeSource signalDMR 2450 bpsTWELP 2400 bps
Disabled
Enabled

 Robustness To The Channel Errors. The diagram and table below show a dependence of the averaged speech quality for AWGN-noisy channel for different BER in comparison with other vocoders.

DMR 3600 bps standard vocoder includes 2450 bps vocoder + FEC that can operate as in "Hard Decisions" mode as well as in "Soft Decision" mode from modem. "Soft decisions" mode provides much better robustness in comparison with the "hard decisions" mode.

 
BER %DMR 2450DMR 3600 (HD)DMR 3600 (SD)
0.00 3.041 3.160 3.160
0.10 2.963 3.159 3.073
0.20 2.890 3.158 2.983
0.30 2.830 3.156 2.925
0.40 2.781 3.155 2.862
0.50 2.734 3.154 2.798
0.60 2.688 3.153 2.727
0.70 2.633 3.152 2.675
0.80 2.587 3.150 2.625
0.90 2.552 3.149 2.568
1.00 2.502 3.148 2.530

Additional Functionalities. The following additional functionalities are developed by DSPINI and integrated into TWELP vocoders:

  • Automatic Gain Control (AGC),
  • Noise Cancellation for Speech Enhancement (NCSE)
  • Voice Activity Detector (VAD),
  • Tone Detection/Generation (Single tones and Dual tones). The tones are transmitted by the vocoder facilities.

Each functionality has unique features, performance and characteristics, providing significant superiority over any well-known implementations on the market.

Technical Characteristics And Resource Requirements:

Technical characteristics
Bit Rate
(bps)
AlgorithmFrame size
(ms)
Algorithmic delay
(including frame size)
(ms)
Sampling rate
(kHz)
Signal formatBit stream format
2400 TWELP 20 40 8 Linear
16-bit
PCM
48
Additional functionalities
NameFunctionalityTechnical characteristics
NameValue
AGC Automatic Gain 
Control
Control range: 0 ... +20 dB
NCSE Noise Canceller -
Speech Enhancer
SNR increasing > 6 dB
Speech quality
improvement
> 0.1 PESQ
Tone
Detector
Single/Dual tones 
detection
In accordance with international standards
Tone
Generator
Single/Dual tones 
generation
Special generator, kept continuity of signal 
(phase and amplitude of signal of previous frame)
VAD Voice Activity 
Detection
Reliable detection speech 
in background noise
CNG Comfort Noise 
Generation
Type of noise "white"
Level - 60 dB

Resources for ARM Cortex-M4 platform
ModuleMIPS*
peak
Memory (KBytes)
ProgramData
ConstantsChannelHeapStack
Voice Encoder 49.3 33 37 4.5 4.8 2.1
NCSE 6.7
AGC 0.2
Voice Decoder 14.4
Voice Encoder +
Voice Decoder
63.7
Total 70.6


Resources for TI's C64 DSP platform
ModuleMIPS*
peak
Memory (KBytes)
ProgramData
ConstantsChannelHeapStack
Voice Encoder 17.6 63 37 4.5 4.8 2.1
NCSE 2.9
AGC 0.1
Voice Decoder 4.1
Voice Encoder +
Voice Decoder
21.7
Total 24.7

Resources (estimated) for TI's C55 DSP platform
ModuleMIPS*
peak
Memory (KBytes)
ProgramData
ConstantsChannelHeapStack
Voice Encoder 30.0 21 37 4.5 4.8 2.1
NCSE 7.0
AGC 0.2
Voice Decoder 10.0
Voice Encoder +
Voice Decoder
40.0
Total 47.2

* DSPINI continues optimization of the TWELP algorithm and code in order to minimize computational complexity of the vocoder.

Guarantee And Support.  DSPINI guarantees a quality and accordance of all technical characteristics of the product to requirement of current specifications. Testing and other method of quality control are used for guarantee support.

Any Platforms.  DSPINI can port this vocoder software into any other DSP, RISC or general- purposes platform inshort time: 1-2 months.

Licensing Terms.  To use the vocoder, customer should obtain:

  • DSPINI's license that gives a right to use our implementation, our software of the DMR vocoder in customer's products. But our license doesn't cover rights of the DVSI company as IP-holder of the MBE-based technology, used in DMR vocoder.
  • DVSI's license that gives a right to use the DMR technology in customer's products. To get this license, customer should contact with DVSI directly.

Customization.  The vocoder can be customized under any specific requirements- other bit rate, frame size, any other robustness to channel errors, etc. Please contact with us for details.

Prospects.  DSPINI is impoving and developing continuously a set of new vocoders with range from 300 bps up to 9600 bps, based on TWELP technology.

Related Software.  This vocoder may be effectively used in a bundle with other DSPINI's products:

  • Linear and acoustic echo cancellers,
  • Multichannel noise cancellers (including two-microphone adaptive array),
  • Wired or radiomodems for any types of channels and bitrates,
  • Other products.

Downloads: