Superior Audio Quality for Digital Radio. TWELP DMR delivers clearer, more natural speech and high-quality reproduction of non-speech signals, including emergency sirens. It is highly robust to acoustic noise, while integrated Noise Cancellation–Speech Enhancement further improves intelligibility in demanding environments.
Enhance New Radios While Preserving the Existing Fleet. TWELP can be added alongside AMBE+2: AMBE+2 maintains communication with existing radios, while TWELP provides the enhanced audio mode when supported by both endpoints. Associated signaling or control data identifies the active vocoder, allowing the receiver to select the appropriate decoder automatically.

TWELP DMR combines a 2450 bps vocoder with 1150 bps UEP-RCPC forward error correction, resulting in a total rate of 3600 bps. By allocating redundancy according to the sensitivity of encoded bits, this joint source–channel coding scheme provides strong protection against radio channel errors.

Designed for DMR, dPMR, marine VHF digital voice, HF radio, and other digital voice applications.

TWELP Technology Features. The vocoder is based on the newest technology of a 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 much better speech quality in comparison with any well-known technologies, including AMBE+2, MELPe, ACELP, etc. at the same bit rate in range from 300 bps up to 9600 bps and beyond. 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 DMR vocoder in a noiseless channel. TWELP DMR vocoder and AMBE+2 DMR 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 an estimation of the speech quality in PESQ terms:

Speech Samples (WAV-files). A few independent experts listened TWELP DMR vocoder in comparison with AMBE+2 DMR vocoder (DVSI's AMBE-3000 chip, Rate#33), using method of preferences. Majority of experts preferred TWELP to AMBE+2, having noted a much more natural human-sounding voice in the TWELP vocoder.
You can listen to the short samples of the source speech as well as the speech processed by both vocoders for any of 20 languages in the table below.
Also, you can download a full set of P.50 samples as zip-files for all languages simultaneously in Downloads section below.

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 the voice makes TWELP vocoders well suitable for replacement of analog radio with 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.

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 a speech quality in a noisy acoustic environment.

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 different BER in comparison with the other vocoders.

We recomend using the TWELP DMR vocoder in "Soft Decisions" mode from a modem. You can see the difference between "Hard Decisions" (HD) and "Soft Decisions" (SD) modes on the diagram below.

You can play and listen to the short samples of the source speech as well as the speech processed by a standard DMR (AMBE+) 3600 bps (vocoder+FEC) and TWELP DMR vocoders (both in SD mode) in AWGN channel with BER = 5% for any of 20 languages in the table below.

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:

* 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 assured that any our software/code doesn't contain any secret functions or features hidden from the user. 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 the requirement of the current specifications. Testing and the 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-purposes platform in a short time: 1-2 months.

Licensing Terms. To use the vocoder software, a 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 us for the details.

Prospects. DSPINI is impoving and developing continuously a set of new vocoders with the 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)
• AMBE+2 2450 bps speech samples (zip)
• TWELP DMR 2450 bps speech samples (zip)
• PC-evaluation package (zip) — at request
• User's Guide document (pdf) — at request