Provides voice communication in hardest conditions where it was impossible before.

For Digital HF Radio 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.

Speech Quality. Here is the comparison with MELPe vocoder, operating on twice higher bit rate 600 bps. TWELP 300 bps vocoder and MELPe 600 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:

A diagram just demonstrates a difference in speech quality for TWELP 300 and MELPe 600 vocoders. Exact numbers are shown in the table below.
LanguageMELPe 600 bpsTWELP 300 bps
American 2.397 2.216
Arabic 2.254 2.068
British 2.414 2.292
Chinese 2.189 2.069
Danish 2.227 2.100
Dutch 2.173 1.973
Finnich 2.249 1.994
French 2.34 2.159
German 2.287 2.163
Greek 2.212 2.083
Hindi 2.403 2.138
Hungarian 2.359 2.097
Italian 2.428 2.334
Japanese 2.436 2.212
Norwegian 2.225 2.014
Polish 2.294 2.074
Portuguese 2.393 2.140
Russian 2.156 2.015
Spanish 2.389 2.137
Swedish 2.43 2.231

A difference is on average 0.187 PESQ

Speech Samples (WAV-files). A few independent experts in HF-radio communication listened TWELP 300 bps vocoder and found that this vocoder provides a satisfactory intellegibility of voice for communication channels with very low (negative) SNR, where analogue radio provides no voice at all, where you can hear a noise only.
You can play and listen short samples of the source speech as well as the speech processed by Analogue Radio and Digital Radio (TWELP 300 bps vocoder + modem) for exactly the same AWGN channel with negative SNR, 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.

Source SpeechAnalogue RadioDigital Radio

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 signalMELPe 600 bpsTWELP 300 bps
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 signalMELPe 600 bpsTWELP 300 bps

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.

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 %MELPe 600TWELP 600 RobustTWELP 480
0.00 2.313 2.389 2.389
0.10 2.251 2.367 2.279
0.20 2.205 2.344 2.209
0.30 2.167 2.33 2.153
0.40 2.104 2.293 2.094
0.50 2.069 2.276 2.046
0.60 2.007 2.257 1.994
0.70 1.971 2.243 1.920
0.80 1.925 2.214 1.893
0.90 1.880 2.194 1.844
1.00 1.845 2.152 1.816

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
300 TWELP 320 340 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)
Voice Encoder 72.5 41 197 4.7 11.3 1.0
NCSE 6.4
AGC 0.2
Voice Decoder 13.3
Voice Encoder +
Voice Decoder
Total 92.4

Resources for TI's C64 DSP platform
Memory (KBytes)
Voice Encoder 25.9 79 197 4.7 11.3 1.0
NCSE 2.8
AGC 0.1
Voice Decoder 3.8
Voice Encoder +
Voice Decoder
Total 32.6

Resources (estimated) for TI's C55 DSP platform
Memory (KBytes)
Voice Encoder 44 51 197 4.7 11.3 1.0
NCSE 6.8
AGC 0.2
Voice Decoder 9.0
Voice Encoder +
Voice Decoder
Total 60

* 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, customer should obtain a license from DSPINI only.

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.