Provides high speech quality as in noiseless channel as well as in very noisy channel. Much better than AMBE+2 (DMR) 3600 bps vocoder.

A "joint source-channel coding" solution on TWELP 2400 bps vocoder base and FEC 1200 bps as UEP-RCPC (Unequal Error Protection Rate Compatible Punctured Convolution) code provides reliable protection of the bits strictly in accordance with their sensitivity to errors.

For Digital HF Radio, Digital Mobile Radio (DMR) and other markets.

TWELP Technology Features. The vocoder is based on newest technology of speech coding called "Tri-Wave Excited Linear Prediction" (TWELP) that was developed by experts of DSPINI. 

TWELP technology is a new class of vocoders that differs from any other LPC-based vocoders by:

  • advance reliable method of pitch estimation
  • pitch-synchronous analysis
  • advance tri-wave model of excitation
  • newest quantization schemes
  • pitch-synchronous synthesis

Thanks to these unique features, TWELP technology provides much better speech quality in comparison with any well-known technologies, including AMBE+2, MELPe, ACELP, etc. on the same bit rate in range from 300 bps up to 9600 bps and more. Moreover, in contrast to other LBR vocoders (like MELPe, etc.) TWELP provides much better quality for non-speech signals like sirens, background music, etc.

Superiority In Speech Quality. Here is the comparison with AMBE+2 3600 bps (DMR) vocoder in noiseless channel. TWELP 3600 bps Robust vocoder and AMBE+2 3600 bps vocoder (DVSI's AMBE-3000 chip, Rate#33, was used) 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:

A diagram demonstrates superiority TWELP 3600 Robust over AMBE+2 3600 in speech quality in clear channel. Exact numbers are shown in the table below.
LanguageTWELP 3600 bps RobustAMBE+2 (DMR) 3600 bps
American 3.304 3.085
Arabic 3.243 3.014
British 3.146 3.072
Chinese 3.290 2.979
Danish 3.270 2.941
Dutch 3.077 2.900
Finnich 3.043 2.867
French 3.310 3.117
German 3.178 2.971
Greek 3.248 2.992
Hindi 3.248 3.097
Hungarian 3.264 3.037
Italian 3.374 3.155
Japanese 3.398 3.151
Norwegian 3.249 2.964
Polish 3.243 2.944
Portuguese 3.312 3.175
Russian 3.140 2.980
Spanish 3.281 3.099
Swedish 3.256 3.053

Superiority of the TWELP 3600 bps Robust vocoder is on average 0.214 PESQ

Speech Samples (WAV-files). A few independent experts listened TWELP 3600 bps Robust vocoder in comparison with AMBE+2 (DMR) 3600 bps vocoder (DVSI's AMBE-3000 chip, Rate#33), using method of preferences. Majority of experts preferred TWELP to AMBE+2, having noted much more natural human-sounding of voice in the TWELP vocoder.
You can play and listen short samples of the source speech as well as the speech processed by both 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 3600 bpsTWELP 3600 bps Robust

Superiority In Quality Of The Non-speech Signals. In contrast to other LBR vocoders (MELPe, AMBE+2, etc.), TWELP vocoders provide high quality of non-speech signals, including police, ambulance, fire sirens, etc. This feature in conjunction with high quality natural human-sounding 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 (DMR) 3600 bpsTWELP 3600 bps Robust
Siren only
With voice

High 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 signalAMBE (DMR) 3600 bpsTWELP 3600 bps Robust

High 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.

We recomend to use the TWELP 3600 Robust vocoder in "Soft Decisions" mode from a modem. You can see a difference between "Hard Decisions" (HD) and "Soft Decisions" (SD) modes on the diagramm below.

BER %AMBE+2 (DMR) 3600TWELP 3600 Robust (HD)TWELP 3600 Robust (SD)
0 3.029 3.244 3.244
1 2.984 3.183 3.194
2 2.943 3.119 3.149
3 2.888 3.011 3.100
4 2.810 2.865 3.052
5 2.711 2.666 2.992

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
3600 TWELP 20 40 8 Linear
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)
Encoder 47.0 36 34 4.6 4.0 2.1
NCSE 6.0
AGC 0.2
Decoder 19.0
Encoder +
Total 72.2

Resources for TI's C64 DSP platform
Memory (KBytes)
Encoder 16.8 69 34 4.6 4.0 2.1
NCSE 2.6
AGC 0.1
Decoder 6.1
Encoder +
Total 29.0

Resources (estimated) for TI's C55 DSP platform
Memory (KBytes)
Encoder 29.0 23 34 4.6 4.0 2.1
NCSE 6.2
AGC 0.2
Decoder 15.0
Encoder +
Total 50.4

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

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 software, customer should obtain a license from DSPINI only.

Also, TWELP 3600 bps Robust vocoder is available as CMX7262 chip from CML Microcircuits

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.