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.
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 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:
|Language||TWELP 2400||AMBE+2 2450||DMR 2450|
An averaged quality of the DMR and AMBE+2 vocoders are exactly the same.
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.
|Language||Source speech||AMBE+2 2450 bps||DMR 2450 bps||TWELP 2400 bps|
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 type||Source signal||DMR 2450 bps||TWELP 2400 bps|
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 Mode||Source signal||DMR 2450 bps||TWELP 2400 bps|
Special "robust" versions of the TWELP vocoders include FEC that are integrated with vocoder on base of "joint source-channel coding" approach that provides high speech quality simultaneously in noisy channel as well as in noiseless channel. FEC can operate with "soft decisions" as well as with "hard decisions" from a modem. "Soft decisions" mode provides much better robustness in comparison with the "hard decisions" mode.
|BER %||DMR 2450||TWELP 3600 Robust||DMR 3600 Robust|
- 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.
(including frame size)
|Signal format||Bit stream format|
|Control range:||0 ... +20 dB|
|NCSE||Noise Canceller -
|SNR increasing||> 6 dB|
|> 0.1 PESQ|
|In accordance with international standards|
|Special generator, kept continuity of signal
(phase and amplitude of signal of previous frame)
|Reliable detection speech
in background noise
|Type of noise||"white"|
|Level||- 60 dB|
|Voice Encoder +
|Voice Encoder +
|Voice Encoder +
* 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.