TWELP™ Vocoder

Moscow, Russia, November 24, 2011 - DSP Innovations Inc. (DSPINI) announces proprietary 2400/3600 bps vocoder, based on the newest speech coding technology TWELP™, for DMR/dPMR 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. The technology provides the best speech quality among competitors today, thanks to:

• Advance reliable method of Pitch estimation
• Pitch synchronous analysis
• Advance tri-wave model of excitation:
  • Voiced Component Excited Wave (VCEW)
  • Unvoiced Component Excited Wave (UCEW)
  • Transient Component Excited Wave (TCEW)
• Newest quantization schemes
• Pitch synchronous synthesis

TWELP technology is not a variety or combination of well-known speech coding methods. It is not WI-based method (PWI, LCWI, ALCWI, etc.), is not sinusoidal/harmonic coding method, including MBE-based coding (IMBE, AMBE, MELP, etc.), is not MPE-based or CELP-based method (MPE-CELP, ACELP, etc). TWELP is unique three-component representation of pitch-synchronous LPC residual. New technology allows to achieve much better speech quality in comparison with any known speech coding methods on the same bit rates (from 600 bps up to 9600 bps and wider).

Superiority in speech quality. Here is the comparison with AMBE+2 vocoder. TWELP 2400 bps vocoder (portable optimized Fixed-Point implementation) and AMBE-3000 HDK (Rate#33: AMBE+2 2450 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 few independent experts tested by listening TWELP vocoder in comparison with AMBE+2 and MELPe 2400, using method of preferences. Majority of experts preferred AMBE+2 to MELPe and significant majority of the experts preferred TWELP to AMBE+2 and MELPe, having noted much more natural human-sounding of voice in the TWELP vocoder.

Superiority in quality of the non-speech signals. In contrast to other LBR vocoders (MELPe, AMBE+2, etc.), TWELP vocoder provides 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 vocoder 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.

High robustness to acoustic noise. In contrast to other LBR vocoders, TWELP vocoder is well robust to acoustic noise thanks to robust reliable method of pitch estimation and other features of TWELP technology.

High Robustness to the channel errors. TWELP 3600 bps vocoder includes FEC (1200 bps) that is integrated with vocoder (2400 bps) 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. Mode of "soft decisions" provides much better robustness in comparison with mode of "hard decisions".

Additional functionalities. The following additional functionalities are developed by DSPINI and integrated into the vocoder:

• 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 through vocoder.

Technical characteristics and resource requirements:

Technical characteristics

Bit Rate w/o FEC / with FEC (bps)	Algorithm	Frame size (ms)	Algorithmic delay (including farme size) (ms)	Sampling rate (kHz)	Signal format	Bit stream format
2400/3600	TWELP	20	40	8	Linear 16-bit PCM	48/72

Additional functionalities

Name	Functionality	Technical characteristics
		Name	Value
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 (including all additional functionalities) for TI's C55 DSP platform

Module	MIPS* peak	Memory (KBytes)
		Program	Data
			Constants	Channel	Stack	Heap
Voice Encoder	18.3	28.6	36.7	4.6	0.5	3.9
FEC Encoder	1
FEC Decoder	2
Voice Decoder	6.5
Total	27.8

* 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 platform. DSPINI can port this vocoder software into any other DSP, RISC or general- purposes platform inshort time: 2-3 months.

Licensing terms. To use the vocoder, customer should obtain a license from DSPINI only.

Low price is another advantage of this vocoder. Please contact us to check it out.

Prospects. DSPINI are developing a set of new vocoders with range from 600 bps up to 9600 bps, based on TWELP technology. DSPINI has already TWELP-based models for 4000 and 6000 bps that provide speech quality much better in comparison with all known modern codecs on the same bit rate (for example, in comparison with ACELP-based AMR GSM codec). In nearest time, DSPINI will test TWELP-based vocoders for 1200 and 600 bps bit rates but already now the company has grounds to declare that speech quality of these vocoders is much better in comparison with MELPe vocoder on the same bit rates.
Please visit the http://twelp.vc web-site to get more information.

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.