Provides very high speech quality - much better than MELPe 2400 bps vocoder and AMBE+2 2450 bps vocoder.

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 MELPe 1200 bps vocoder in noiseless channel. TWELP 2400 bps vocoder, MELPe 2400 bps vocoder and AMBE+2 2450 bps vocoder (DVSI's AMBE-3000 chip, rate 33) 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 of the TWELP 2400 bps over MELPe 2400 bps and AMBE+2 2450 bps in speech quality in clear channel. Exact numbers are presented in the table below.
LanguageTWELP 2400MELPe 2400AMBE+2 2450
American 3.247 3.077 3.085
Arabic 3.157 3.053 3.014
British 3.106 3.019 3.072
Chinese 3.192 2.970 2.979
Danish 3.184 3.022 2.941
Dutch 3.004 2.830 2.900
Finnich 2.970 2.791 2.867
French 3.135 3.106 3.117
German 3.121 2.998 2.971
Greek 3.140 3.004 2.992
Hindi 3.152 3.089 3.097
Hungarian 3.192 3.086 3.037
Italian 3.325 3.226 3.155
Japanese 3.261 3.188 3.151
Norwegian 3.173 3.032 2.964
Polish 3.178 3.029 2.944
Portuguese 3.191 3.146 3.175
Russian 3.076 2.952 2.980
Spanish 3.201 3.048 3.099
Swedish 3.203 3.147 3.053
Average3.16043.04073.0297

Superiority of the TWELP 2400 bps vocoder is on average 0.12 and 0.13 PESQ appropriately


Speech Samples (WAV-files). A few independent experts listened TWELP 2400 bps vocoder in comparison with MELPe 2400 bps vocoder and AMBE+2 2450 bps vocoder, using method of preferences. Majority of experts preferred TWELP to MELPe and 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 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 2450 bpsMELPe 2400 bpsTWELP 2400 bps
American
Arabic
British
Chinese
Danish
Dutch
Finnich
French
German
Greek
Hindi
Hungarian
Italian
Japanese
Norwegian
Polish
Portuguese
Russian
Spanish
Swedish

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 2400 bpsTWELP 2400 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 2400 bpsTWELP 2400 bps
Disabled
Enabled

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 2400TWELP 3600 RobustTWELP 2400
0.00 3.041 3.160 3.160
0.10 2.963 3.159 3.073
0.20 2.890 3.158 2.983
0.30 2.830 3.156 2.925
0.40 2.781 3.155 2.862
0.50 2.734 3.154 2.798
0.60 2.688 3.153 2.727
0.70 2.633 3.152 2.675
0.80 2.587 3.150 2.625
0.90 2.552 3.149 2.568
1.00 2.502 3.148 2.530

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
(bps)
AlgorithmFrame size
(ms)
Algorithmic delay
(including frame size)
(ms)
Sampling rate
(kHz)
Signal formatBit stream format
2400 TWELP 20 40 8 Linear
16-bit
PCM
48
Additional functionalities
NameFunctionalityTechnical characteristics
NameValue
AGC Automatic Gain 
Control
Control range: 0 ... +20 dB
NCSE Noise Canceller -
Speech Enhancer
SNR increasing > 6 dB
Speech quality
improvement
> 0.1 PESQ
Tone
Detector
Single/Dual tones 
detection
In accordance with international standards
Tone
Generator
Single/Dual tones 
generation
Special generator, kept continuity of signal 
(phase and amplitude of signal of previous frame)
VAD Voice Activity 
Detection
Reliable detection speech 
in background noise
CNG Comfort Noise 
Generation
Type of noise "white"
Level - 60 dB

Resources for ARM Cortex-M4 platform
ModuleMIPS*
peak
Memory (KBytes)
ProgramData
ConstantsChannelHeapStack
Voice Encoder 49.3 33 37 4.5 4.8 2.1
NCSE 6.7
AGC 0.2
Voice Decoder 14.4
Voice Encoder +
Voice Decoder
63.7
Total 70.6


Resources for TI's C64 DSP platform
ModuleMIPS*
peak
Memory (KBytes)
ProgramData
ConstantsChannelHeapStack
Voice Encoder 17.6 63 37 4.5 4.8 2.1
NCSE 2.9
AGC 0.1
Voice Decoder 4.1
Voice Encoder +
Voice Decoder
21.7
Total 24.7

Resources (estimated) for TI's C55 DSP platform
ModuleMIPS*
peak
Memory (KBytes)
ProgramData
ConstantsChannelHeapStack
Voice Encoder 30.0 21 37 4.5 4.8 2.1
NCSE 7.0
AGC 0.2
Voice Decoder 10.0
Voice Encoder +
Voice Decoder
40.0
Total 47.2

* 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 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.

Downloads: