(version 5.0) offers speech quality and intelligibility that were previously achievable only at double or higher bitrates. Below are the results of comparative tests with the MELPe 2400 bps vocoder and with 3GPP AMR-NB 4750 bps vocoder, which operates at twice the bitrate.

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 significantly better speech quality than other well-known technologies—including AMBE+2, MELPe, ACELP, and others—at equivalent bit rates ranging from 300 bps to 4800 bps and beyond.

Additionally, unlike other low-bitrate vocoders (such as MELPe, for example), TWELP delivers much higher quality for non-speech signals, including sirens, background music, and similar audio.

Note: 
We have updated the speech database by minimizing inter-speech pauses to eliminate their impact on the evaluation results. Therefore, the numbers obtained from the quality measurements using this updated speech database differ from those previously obtained with the original speech database, where speech pauses were not removed.

Speech Samples (WAV-files). 
A few independent experts compared the TWELP 2400 bps vocoder with the AMR-NB 4750 bps and MELPe 2400 bps vocoders using the preference method.
Although opinions were almost evenly split, the majority of listeners preferred the TWELP vocoder over the AMR-NB vocoder, noting that the speech sounded clearer and more natural. All listeners preferred the TWELP vocoder over the MELPe vocoder, noting that the speech sounded more natural and less synthetic.

You can play and listen to short samples of the source speech, as well as the speech processed by the AMR-NB 4750 bps vocoder, MELPe 2400 bps vocoder and the TWELP 2400 bps vocoder, using the links in the table below.

For the best listening experience, we recommend using high-quality headphones or premium audio equipment to hear the nuances and differences in the vocoder sound more clearly.

You can also download the complete set of P.50 samples as zip files for all languages simultaneously by using the links in the 'Downloads' section at the bottom of the page.

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.

Additional Functionalities. The following additional functionalities are developed by DSPINI and integrated into TWELP vocoders:

• Noise Cancellation Speech Enhancement (NCSE)
• Automatic Gain Control (AGC),
• Voice Activity Detector (VAD),
• Discontinuous Transmission (DTX),
• Tone Detection/Generation (Single tones and Dual tones). The tones are transmitted by the vocoder facilities.

Note: 
The Tone Detector/Generator functionalities are not integrated into the code by default but can be added free of charge upon request.

Each functionality has unique features, performance and characteristics, providing significant superiority over any well-known implementations on the market.

Technical Characteristics And Resource Requirements:

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

Software Integrity and Security. DSPINI guarantees the ABSOLUTE integrity of its software, free from any undocumented features, undeclared capabilities, or hidden functions. Our customers can be assured that none of our software/code contains any secret features or functionalities concealed from the user. If necessary, we are ready to provide the source code of our software products for appropriate certification.
Moreover, our software is available in source code form—you simply need to purchase the appropriate license to use it.

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:

• Datasheet (pdf)
• ITU-T P.50 source speech samples (zip)
• AMR-NB 4750 bps speech samples (zip)
• MELPe 2400 bps speech samples (zip)
• TWELP 2400 bps speech samples (zip)
• P.862 and STOI/ESTOI utilities
• PC-evaluation package (zip) — on request
• User's Guide document (pdf) — on request