153 research outputs found
DESIGN AND EVALUATION OF HARMONIC SPEECH ENHANCEMENT AND BANDWIDTH EXTENSION
Improving the quality and intelligibility of speech signals continues to be an important topic in mobile communications and hearing aid applications. This thesis explored the possibilities of improving the quality of corrupted speech by cascading a log Minimum Mean Square Error (logMMSE) noise reduction system with a Harmonic Speech Enhancement (HSE) system. In HSE, an adaptive comb filter is deployed to harmonically filter the useful speech signal and suppress the noisy components to noise floor. A Bandwidth Extension (BWE) algorithm was applied to the enhanced speech for further improvements in speech quality. Performance of this algorithm combination was evaluated using objective speech quality metrics across a variety of noisy and reverberant environments. Results showed that the logMMSE and HSE combination enhanced the speech quality in any reverberant environment and in the presence of multi-talker babble. The objective improvements associated with the BWE were found to be minima
A Band Extension Technique for Narrow-Band Telephony Speech Based on Full Wave Rectification
This study investigates a band extension technique for narrow-band telephony speech. The proposed technique employs full wave rectification that nonlinearly generates high-band overtones from the low band. In order to improve the conventional technique, this study investigates a frame-by-frame gain control based on the estimation of gain parameter from narrow-band telephony speech. A subjective evaluation indicates that the proposed technique outperforms the conventional technique
Glottal-synchronous speech processing
Glottal-synchronous speech processing is a field of speech science where the pseudoperiodicity
of voiced speech is exploited. Traditionally, speech processing involves segmenting
and processing short speech frames of predefined length; this may fail to exploit the inherent
periodic structure of voiced speech which glottal-synchronous speech frames have
the potential to harness. Glottal-synchronous frames are often derived from the glottal
closure instants (GCIs) and glottal opening instants (GOIs).
The SIGMA algorithm was developed for the detection of GCIs and GOIs from
the Electroglottograph signal with a measured accuracy of up to 99.59%. For GCI and
GOI detection from speech signals, the YAGA algorithm provides a measured accuracy
of up to 99.84%. Multichannel speech-based approaches are shown to be more robust to
reverberation than single-channel algorithms.
The GCIs are applied to real-world applications including speech dereverberation,
where SNR is improved by up to 5 dB, and to prosodic manipulation where the importance
of voicing detection in glottal-synchronous algorithms is demonstrated by subjective
testing. The GCIs are further exploited in a new area of data-driven speech modelling,
providing new insights into speech production and a set of tools to aid deployment into
real-world applications. The technique is shown to be applicable in areas of speech coding,
identification and artificial bandwidth extension of telephone speec
Recent Advances in Steganography
Steganography is the art and science of communicating which hides the existence of the communication. Steganographic technologies are an important part of the future of Internet security and privacy on open systems such as the Internet. This book's focus is on a relatively new field of study in Steganography and it takes a look at this technology by introducing the readers various concepts of Steganography and Steganalysis. The book has a brief history of steganography and it surveys steganalysis methods considering their modeling techniques. Some new steganography techniques for hiding secret data in images are presented. Furthermore, steganography in speeches is reviewed, and a new approach for hiding data in speeches is introduced
The removal of environmental noise in cellular communications by perceptual techniques
This thesis describes the application of a perceptually based spectral subtraction algorithm for
the enhancement of non-stationary noise corrupted speech. Through examination of speech enhancement
techniques, explanations are given for the choice of magnitude spectral subtraction
and how the human auditory system can be modelled for frequency domain speech enhancement.
It is discovered, that the cochlea provides the mechanical speech enhancement in the
auditory system, through the use of masking. Frequency masking is used in spectral subtraction,
to improve the algorithm execution time, and to shape the enhancement process making it
sound natural to the ear.
A new technique for estimation of background noise is presented, which operates during speech
sections as well as pauses. This uses two microphones placed on opposite ends of the cellular
handset. Using these, the algorithm determines whether the signal is speech, or noise, by
examining the current and next frames presented to each microphone. This allows operation in
non-stationary conditions, as the estimation is calculated for each frame, and a speech pause is
not required for updating. A voting decision process decides the presence of speech or noise
which determines which microphone the estimation is calculated from.
The importance of an accurate noise estimate is highlighted with a new technique to reduce
the effect of musical noise artifacts in the processed speech. This is a classic drawback of
spectral subtraction techniques, and it is shown, that the trade off between noise reduction and
speech distortion can be extended by this process. A new method for dealing with musical
noise is described, which uses a combination of energy and variance examination of the spectrogram
to segregate potential musical noise from desired speech sections. By examination of
the spectrogram points surrounding musical noise sections, perceptually relevant values replace
the corruption leading to cleaner enhanced speech.
Any perceptual speech system requires accurate estimates of the clean speech masking thresholds,
to prevent noisy sections being passed through the enhancement untouched. In this thesis, a
method for the calculation of the estimated clean speech masking thresholds is derived. Classically,
this requires an estimation of the clean speech before the thresholds can be derived,
but this results in inaccuracy due to the presence of musical noise and spectral nulls. The
new algorithm examines the thresholds produced by the corrupted speech, and the background
noise, and from these determines the relationship between the two, to produce an estimate of
the clean thresholds, with no operation performed on the actual speech signal. A discrepancy is
found between the results for male and female speech, which, by examination of the perceptual
process, is shown to be due to the different formant positions in male and female speech.
Following the development of these parts, the entire enhancement algorithm is tested on a range
of noise scenarios, using male and female speech. The results show, that the proposed algorithm
is able to provide adequate performance in terms of noise reduction and speech quality
Early FM Radio
The commonly accepted history of FM radio is one of the twentieth century’s iconic sagas of invention, heroism, and tragedy. Edwin Howard Armstrong created a system of wideband frequency-modulation radio in 1933. The Radio Corporation of America (RCA), convinced that Armstrong’s system threatened its AM empire, failed to develop the new technology and refused to pay Armstrong royalties. Armstrong sued the company at great personal cost. He died despondent, exhausted, and broke. But this account, according to Gary L. Frost, ignores the contributions of scores of other individuals who were involved in the decades-long struggle to realize the potential of FM radio. The first scholar to fully examine recently uncovered evidence from the Armstrong v. RCA lawsuit, Frost offers a thorough revision of the FM story. Frost’s balanced, contextualized approach provides a much-needed corrective to previous accounts. Navigating deftly through the details of a complicated story, he examines the motivations and interactions of the three communities most intimately involved in the development of the technology—Progressive-era amateur radio operators, RCA and Westinghouse engineers, and early FM broadcasters. In the process, Frost demonstrates the tension between competition and collaboration that goes hand in hand with the emergence and refinement of new technologies. Frost's study reconsiders both the social construction of FM radio and the process of technological evolution. Historians of technology, communication, and media will welcome this important reexamination of the canonic story of early FM radio
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