is AMBE+2 compatible DMR (ETSI TS 102 361) / dPMR (ETSI TS 102 658) standard vocoder. 

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

 Technology Features. The 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 DMR vocoders. TWELP DMR vocoder, DVSI's AMBE+2 DMR vocoder (DVSI's AMBE-3000 chip, rate 33) and DSPINI's AMBE+ DMR 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 (AMBE+ DMR) provides speech quality on average very close to DVSI's AMBE+2 DMR vocoder- a difference is not significant.
TWELP DMR vocoder provides much better speech quality in comparison with both MBE-based vocoders. 
Exact numbers are presented in the table below.
American 3.361 3.085 3.059
Arabic 3.264 3.014 2.981
British 3.220 3.072 2.957
Chinese 3.309 2.979 2.911
Danish 3.308 2.941 2.953
Dutch 3.126 2.900 2.826
Finnich 3.068 2.867 2.755
French 3.373 3.117 2.983
German 3.237 2.971 2.923
Greek 3.283 2.992 2.888
Hindi 3.276 3.097 2.969
Hungarian 3.302 3.037 2.965
Italian 3.427 3.155 3.111
Japanese 3.389 3.151 3.089
Norwegian 3.310 2.964 2.951
Polish 3.269 2.944 2.895
Portuguese 3.321 3.175 3.046
Russian 3.192 2.980 2.958
Spanish 3.286 3.099 2.994
Swedish 3.293 3.053 2.952

A difference in quality of the DSPINI's AMBE+ DMR and DVSI's AMBE+2 DMR vocoders is not too big- 0.072 PESQ.
Superiority of the TWELP DMR vocoder over AMBE+2 is on average 0.251 PESQ.

Speech Samples (WAV-files). A few independent experts listened AMBE+ DMR vocoder in comparison with AMBE+2 DMR vocoder and TWELP DMR vocoder, using method of preferences.
A majority of experts agreed that a difference in sounding between DVSI's and DSPINI's implementations of the DMR standard is not significant, having noted much more natural human-sound of voice in the TWELP DMR 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 DMRAMBE+ DMRTWELP DMR

 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 signalAMBE+ DMRTWELP DMR
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.


 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. As rule, "Soft decisions" mode provides much better robustness in comparison with the "hard decisions" mode. However, our advance implementation of the FEC Decoder allowed to reach very high robustness even in "Hard Decision" mode.

BER %DMR 2450DMR 3600 (HD)DMR 3600 (SD)
0 2.958 2.958 2.958
1 2.575 2.917 2.914
2 2.315 2.868 2.873
3 2.121 2.811 2.825
4 1.963 2.736 2.743
5 1.827 2.618 2.653

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
AlgorithmFrame size
Algorithmic delay
(including frame size)
Sampling rate
Signal formatBit stream format
2450/3600 AMBE+* 20 32 8 Linear

* AMBE+ technology was updated by DSPINI to improve analysis and synthesis as well as to add additional functionalities.

Additional functionalities
NameFunctionalityTechnical characteristics
AGC Automatic Gain 
Control range: 0 ... +20 dB
NCSE Noise Canceller -
Speech Enhancer
SNR increasing > 6 dB
Speech quality
> 0.1 PESQ
Single/Dual tones 
In accordance with international standards
Single/Dual tones 
Special generator, kept continuity of signal 
(phase and amplitude of signal of previous frame)
VAD Voice Activity 
Reliable detection speech 
in background noise
CNG Comfort Noise 
Type of noise "white"
Level - 60 dB

Resources for ARM Cortex-M4 platform
Memory (KBytes)
Voice Encoder 70.0 44.5 23.4 8.6 9.4 1.4
FEC Encoder 0.3
NCSE 3.0
AGC 0.3
FEC Decoder 5.0
Voice Decoder 63.0
Voice Encoder +
Voice Decoder
Total 142.0

Resources for TI's C674x DSP platform
Memory (KBytes)
Voice Encoder 14.7 84 52 12.2 11.0 1.0
FEC Encoder 0.1
NCSE 0.3
AGC 0.5
FEC Decoder 0.8
Voice Decoder 8.5
Voice Encoder +
Voice Decoder
Total 24.9

Resources (estimated) for TI's C55 DSP platform
Memory (KBytes)
Voice Encoder 58.0 39.5 32.2 8.2 9.4 1.4
FEC Encoder 0.2
NCSE 2.4
AGC 0.3
FEC Decoder 5.0
Voice Decoder 38.0
Voice Encoder +
Voice Decoder
Total 102.0

* DSPINI continues optimization of the DMR-vocoder implementation in order to minimize computational complexity of the vocoder. Therefore, please contact with us to get last actul numbers of the resources.

Vulnerability / Security. DSPINI guarantees ABSOLUTE cleanliness of the software from any undocumented features, undeclared capabilities, etc. All our customers can be sure that any our software/ code doesn't contain any secret functions and features hidden from user. We are ready to provide source codes of our software products for an appropriate certification if need.

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.