ASR systems

Currently, mel-scale cepstral coeflicients, and perceptual linear prediction coefficients transformed into cepstral coefficients, are popular choices for the above reasons. Specifically they are ehosen because they are robust to noise, can be modelled with diagonal covariance, and with the aid of the perceptual scaling are more discriminative than would otherwise be. From a speech synthesis point of view, these points are worth making, not because the same requirements exist for synthesis, but rather to make the reader aware that the reason MFCCs and PLPs are so often used in ASR systems is for the above reasons, and not because they are intrinsically better in any general purpose sort of way. This also helps explain why there are so many speech representations in the first place each has strengths in certain areas, and will be used as the application demands. In fact, as we shall see in Chapter 16, the application requirements which make, say, MFCCs so suitable for speeeh recognition are almost entirely absent for our purposes. We shall leave a discussion as to what representations really are suited for speech synthesis purposes until Chapter 16. 

We now turn to techniques used to synthesize speech from cepstral representations and in particular the mel-frequency cepstral coefficients (MFCCs) commonly used in ASR systems. Synthesis from these is not actually a common second generation technique, but it is timely to introduce this technique here as it is effectively performing the same job as pure second generation techniques. In Chapter 15 we will give a full justification for wanting to synthesise from MFCCs, but the main reason is that they are a representation that is highly amenable to robust statistical analysis because the coefficients are statistically independent of one another. 

The input to an ASR system is a sequence of frames of speech, known as observations and denoted... 

Cambridge University and IBM The HMM system developed by Rob Donovan initially at Cambridge University [140], and then at IBM, is notable as one of the systems independent Irom the ATR family. It was based on Cambridge University s HTK ASR system, and used decision trees to segment and cluster state sized units [138], [150], [196]. Particularly interesting recent developments have concerned expressiveness and emotion in text-to-speech [151] [195]. 

It is partly for this reason that we find that mel-frequency cepstral coefficients (MFCCs) are used as the representation of choice in many ASR systems (in addition, they are deemed to have good discrimination properties and are somewhat insensitive to differences between speakers). It is important to note, however, that HMMs themselves are neutral with respect to the type of observation used, and in principle we could use any of... 

General introductions to HMMs can be found in [224], [243]. The original papers on HMMs include Baum et al. [36], Viterbi [476], Baker [33] and Jelinek et al. [237]. These are mentioned for purposes of general interest the ASR systems of today are quite different and, apart from the basic principle, not too much of that early work has survived in today s systems. The best practical guide to modern HMM systems is Cambridge University s HTK system [510]. This is a general-purpose practical toolkit that allows quick and easy building of elementary ASR systems, and serves as the basis... 

Automatic speech recognition (ASR), in which the individual uses sounds, letters, or words as a selection method, is another alternative to keyboard input. In most such systems, the speech recognition is speaker-dependent, and the user trains the system to recognize his or her voice by producing several samples of the same element (Comerford et al., 1997). ASR system use is increasing in the mainstream commercial market for use on the Internet, dictation, general telephone use, and most other computer activities. Persons with disabilities will be the beneficiaries of this expanded use of ASR systems. These systems all use continuous ASR techniques in which the user can speak in almost normal patterns with slight pauses between words. 

Often the microphones supplied with ASR systems are not adequate when the user has limited breath support, special positioning requirements, or low-volume speech (Anson, 1997). Many individuals who have disabilities may not be able to independently don and doff headset microphones that are normally supplied with commercial ASR systems. In Aese cases, desk-mounted types are often used. Current ASR systems utilize commonly available sound cards rather than separate hardware installed in the computer (Anson, 1999). 

Protection and disclaimer statements should be used liberally. As with the ASRS system, where reporters must report within ten days to avoid fines and penalties for unintentional violations, incentives in a health care reporting system can promote timely reporting. 

Koti ASR, Periasamy N (2001) Application of time resolved area normalized emission spectroscopy to multicomponent systems. J Chem Phys 115(15) 7094-7099... 

Ruland and Smarsly [84] study silica/organic nanocomposite films and elucidate their lamellar nanostructure. Figure 8.47 demonstrates the model fit and the components of the model. The parameters hi and az (inside H ) account for deviations from the ideal two-phase system. Asr is the absorption factor for the experiment carried out in SRSAXS geometry. In the raw data an upturn at. s o is clearly visible. This is no structural feature. Instead, the absorption factor is changing from full to partial illumination of the sample. For materials with much stronger lattice distortions one would mainly observe the Porod law, instead - and observe a sharp bend - which are no structural feature, either. 

Three- and five-membered rings (AS2S and AS2S3) have also been structurally characterised for the arsenic-sulfur system. The diarsathiiran cyclo-(RAs)2S [R = C(SiMe3)3] is prepared by the addition of sulfur to the diarsene RAs=AsR. The non-planar five-membered ring cyclo-(PhAs)2S3 is obtained, in addition to cyclo-(PhAsS)4, from treatment of phenylarsenic acid with aqueous ammonia and hydrogen sulfide. ... 

ASR provides an open EM system far from thermodynamic equilibrium in its violent energy exchange with the active vacuum. As is well known, an open dissipative system in disequilibrium with an active environment is permitted to... 

Suppose AHr and ASR are both negative. In this case ASR opposes aggregation while AHr favors it. Since the resistance to aggregation decreases with decreasing temperature, aggregation is expected as T is lowered. Poly(12-hydroxystearic acid) adsorbed from n-heptane and polyoxyethylene adsorbed from methanol are examples of systems that display a CFT with decreasing temperature. Since ASR is the source of the stabilization in these cases, this mechanism is called entropic stabilization. 

The proteins of milk fall into several classes of polypeptide chains. These have been delineated most completely in bovine milk, and a system of nonmenclature has been developed for them (Chapter 3 Eigel et al. 1984). One group, called caseins, consists of four kinds of polypeptides asr, as2-. and 3-, and k- with some genetic variants, post translational modifications, and products of proteolysis. Almost all of the caseins are associated with calcium and phosphate in micelles 20-300 fim in diameter (see Chapter 9). The other milk proteins, called whey proteins, are a diverse group including /3-lactoglobulin, a-lactalbumin, blood serum albumin, and immunoglobulins (Chapter 3). Almost all... 

Teletype. The Teletype is an ASR-33, with a printing speed of 10 characters per second. All user communication, including output, in the basic system is implemented through the Teletype. 

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