Robust Advanced Low Complexity Waveform Interpolation (RALCWI) is a low bit-rate algorithm for vocoder implementation; licensed to Spirit DSP.
RALCWI technology uses unique proprietary signal decomposition and parameter encoding methods, ensuring high voice quality at high compression ratios. The voice quality of RALCWI-class Vocoders, as estimated by independent listeners, is similar to that provided by standard Vocoders running at bit rates above 4000 bps. The Mean Opinion Score (MOS) of voice quality for this Vocoder is about 3.5-3.6. This value was determined by a paired comparison method, performing listening tests of developed and standard voice Vocoders.
The RALCWI Vocoder operates on a “frame-by-frame” basis. The 20ms source voice frame consists of 160 samples of linear 16-bit PCM sampled at 8 kHz. The Voice Encoder performs voice analysis at the high time resolution (8 times per frame) and forms a set of estimated parameters for each voice segment. All of the estimated parameters are quantized to produce 41-, 48- or 55-bit frames, using Vector Quantization (VQ) of different types. All of the vector quantizers were trained on a mixed multi-language voice base, which contains voice samples in both Eastern and Western languages.
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Waveform-Interpolative (WI) vocoder was developed in AT&T Bell Laboratories around 1995 by W.B. Kleijn, and subsequently a low- complexity version was developed by AT&T for the DoD secure vocoder competition. Notable enhancements to the WI coder were made at UCSB. AT&T holds the core patents related to WI, and other institutes hold additional patents. Using these patents as a part of WI coder implementation requires licensing from all IPR holders.
The product is the result of a co-operation between CML Microcircuits and SPIRIT DSP. The co-operation combines CML’s 39-year history of developing mixed-signal semiconductors for professional and leisure communication applications, with SPIRIT’s experience in embedded voice products.
Since inception in 1992 SPIRIT is a Russian company that implements mostly standard audio and data communication software products, primarily outside the US.
Founded in 1968, CML Microcircuits are involved in the design, development and supply of low-power analogue, digital and mixed-signal semiconductors for telecommunications systems worldwide. CML IC’s, the CMX608, CMX618 and the CMX638 market to worldwide communication markets based upon SPIRIT’s proprietary Low Bit-Rate Vocoder technology.