Provides good speech quality and robustness to the channel errors at very low consumption of the computing resources and memory (~2.5 times less than MELPe).
For low cost Digital HF Radio, Digital Mobile Radio (DMR), Voice Storage devices and other markets.
SPRTM model is based simultaneously on two well-known models: Sinusoidal (Harmonic) Coding (SHC) and Linear Predictive Coding (LPC), where system function is presented by LPC-filter and excitation function is formed by Sinusoidal Harmonic model.
However, SPR model uses more complex excitation of the synthesize LPC-filter that contains three components:
- voiced (sinusoidal harmonics of the “fundamental frequency”),
- unvoiced (noise),
- pulsed (aperiodic pulses)
As rule, the first two components are used in Sinusoidal Coding, and third component is used in Multi-Pulse Excitation coding on high bit rates.
We combined advantages of these models to achieve high speech quality at low bit rate and low resources costs.
So, for example, SHC model can’t represent complex speech intervals with aperiodic fluctuations of vocal chords. However, such intervals can be represented by pulse excitation very well. And vise versa, MPE- model can’t provide high speech quality if number of pulses is not enough, therefore this model is used on relatively high bit rates (more 4500 bps).
The combining of these models to form an excitation signal for LPC- model allows achieving unique characteristics of vocoders based on the SPR model.
Therefore, bit stream on output of the Voice Encoder contains the following quantized parameters:
- LPC-parameters (as LSF),
- “Fundamental frequency” (Pitch),
- Frequency-depended Voiced/Unvoiced decisions,
- Pulse parameters,
Speech Quality. Here is the comparison with MELPe 1200 bps vocoder in noiseless channel. SPR 1200 bps vocoder, MELPe 1200 bps vocoder and TWELP 1200 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:
|Language||TWELP 1200||MELPe 1200||SPR 1200|
Superiority of the MELPe 1200 bps vocoder over SPR 1200 bps vocoder in noiseless channel is on average 0.114 PESQ
Speech Samples (WAV-files). A few independent experts listened SPR 1200 bps vocoder in comparison with MELPe 1200 bps vocoder and TWELP 1200 bps vocoder, using method of preferences. Majority of experts preferred TWELP to SPR and MELPe, having noted much more natural human-sounding of voice in the TWELP vocoder. Experts haven't found significant difference in sounding between SPR 1200 and MELPe 1200 vocoders.
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.
|Language||Source speech||MELPe 1200 bps||SPR 1200 bps||TWELP 1200 bps|
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 type||Source signal||MELPe 1200 bps||SPR 1200 bps||TWELP 1200 bps|
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 Mode||Source signal||MELPe 1200 bps||SPR 1200 bps||TWELP 1200 bps|
SPR vocoder is robust already to the channel errors. Also, special "robust" versions of the SPR and 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 1200||TWELP 1600 Robust||SPR 1200|
- 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.
(including frame size)
|Signal format||Bit stream format|
|Control range:||0 ... +20 dB|
|NCSE||Noise Canceller -
|SNR increasing||> 6 dB|
|> 0.1 PESQ|
|In accordance with international standards|
|Special generator, kept continuity of signal
(phase and amplitude of signal of previous frame)
|Reliable detection speech
in background noise
|Type of noise||"white"|
|Level||- 60 dB|
* DSPINI continues optimization of the SPR algorithm and code in order to minimize computational complexity of the vocoder.
Vulnerability / Security. DSPINI guarantees ABSOLUTE cleanliness of the software from any undocumented features, undeclared capabilities, etc. All our customers can be sure that any our software/ code doesn't contain any secret functions and features hidden from user. We are ready to provide source codes of our software products for an appropriate certification if need.
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 SPR and TWELP technologies.
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.