A unique high speech quality for such a very low bit rate — better than MELPe at 600 bps.

For Digital HF Radio and other markets.

TWELP Technology Features. The vocoder is based on the 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 in:

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

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

Superiority In Speech Quality. Here is a comparison with MELPe vocoder, operating on 600 bps. TWELP 480 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 an estimation of a speech quality in PESQ terms:

The diagram demonstrates superiority of TWELP 480 over MELPe 600 in a speech quality. Exact numbers are shown in the table below.
LanguageTWELP 480 bpsMELPe 600 bps
American 2.450 2.397
Arabic 2.318 2.254
British 2.523 2.414
Chinese 2.351 2.189
Danish 2.377 2.227
Dutch 2.225 2.173
Finnich 2.279 2.249
French 2.434 2.34
German 2.376 2.287
Greek 2.318 2.212
Hindi 2.423 2.403
Hungarian 2.410 2.359
Italian 2.548 2.428
Japanese 2.510 2.436
Norwegian 2.312 2.225
Polish 2.347 2.294
Portuguese 2.416 2.393
Russian 2.302 2.156
Spanish 2.393 2.389
Swedish 2.474 2.43

Superiority of the TWELP 480 is on average 0.08 PESQ

Speech Samples (WAV-files). A few independent experts listened to TWELP 480 bps vocoder in comparison with MELPe 600 bps vocoder, using a method of preferences. Majority of experts preferred TWELP to MELPe, having noted a 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 speechMELPe 600 bpsTWELP 480 bps

Superiority In Quality Of The Non-speech Signals. In contrast to other LBR vocoders (MELPe, AMBE+2, etc.), TWELP vocoders provide a high quality of non-speech signals, including police, ambulance, fire sirens, etc. This feature in conjunction with a high quality natural human-sounding of voice makes TWELP vocoders well suitable for replacement of an analog radio by a digital radio and also for other applications where a high quality transmission of non-speech signals is relevant along with a high quality transmission of speech signals.

Source typeSource signalMELPe 600 bpsTWELP 480 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 a robust reliable method of a pitch estimation and other features of TWELP technology.

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

NCSE ModeSource signalMELPe 600 bpsTWELP 480 bps

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

Special "robust" versions of the TWELP vocoders include FEC that is integrated with the vocoder on base of "joint source-channel coding" approach that provides a high speech quality simultaneously in a noisy channel as well as in a noiseless channel. FEC can operate with "soft decisions" as well as with "hard decisions" from a modem. "Soft decisions" mode provides a much better robustness in comparison with the "hard decisions" mode. 

BER %MELPe 600TWELP 600 RobustTWELP 480
0.00 2.313 2.383 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 a 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
480 TWELP 100 120 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 the international standards
Single/Dual tones 
Special generator, kept continuity of a signal 
(phase and amplitude of signal of previous frame)
VAD Voice Activity 
Reliable detection speech 
in a background noise
CNG Comfort Noise 
Type of noise "white"
Level - 60 dB

Resources for ARM Cortex-M4 platform
Memory (KBytes)
Voice Encoder 56.3 38 153 4.6 5.0 1.0
NCSE 6.5
AGC 0.2
Voice Decoder 13.7
Voice Encoder +
Voice Decoder
Total 76.7

Resources for TI's C64 DSP platform
Memory (KBytes)
Voice Encoder 20.1 72 153 4.6 5.0 1.0
NCSE 2.8
AGC 0.1
Voice Decoder 3.9
Voice Encoder +
Voice Decoder
Total 26.9

Resources (estimated) for TI's C55 DSP platform
Memory (KBytes)
Voice Encoder 34 23 153 4.6 5.0 1.0
NCSE 6.7
AGC 0.2
Voice Decoder 10.0
Voice Encoder +
Voice Decoder
Total 50.9

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

Vulnerability / Security. DSPINI guarantees an ABSOLUTE cleanliness of the software from any undocumented features, undeclared capabilities, etc. All our customers can be sure that none of our software/ code contains secret functions or hiiden features. We are ready to provide the source codes of our software products for an appropriate certification, if needed.

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

Any Platforms. DSPINI can port this vocoder software onto any other DSP, RISC or general-purpose platform in a short 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 the 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.