Electromechanical modeling and properties of the electret film EMFI

An electromechanical film can be manufactured with different thickness and elasticity. The thickness for sensor and actuator applications is typically between 30 and 70 μm. The film is modeled using a simplified structure, which shows the reciprocity of the sensor and actuator operation models. The value of the transducer constant depends on the ambient temperature and increases at higher temperatures. During aging the transducer constant begins to decrease permanently at 323 K, but some sensitivity remains even at 333 K. Corona charging that gives a sensitivity value ~200 pCN^-1 for HS01 type film is preferred over electron beam charging. The development of such films is aimed at sensor and actuator applications. An interesting field is the active control of sound where flat and efficient microphones and loudspeakers are needed     

Energy-based effective length of the impulse response of arecursive filter

A measure for the effective length of the impulse response of a stable recursive digital filter based on accumulated energy is proposed. The new measure finds applications in several fields of digital signal processing, including estimation of the extent of attack transients for filters with dynamically varying inputs, elimination of transients in variable recursive filters, and design and implementation of linear-phase IIR systems. A general definition and a simple algorithm to evaluate it are introduced, and closed-form expressions are derived for first and second-order all-pole filters. The effect of zeros on the effective length is analyzed. An upper bound for the effective length of higher-order filters is derived using results for low-order filters, which is illustrated for classical digital lowpass filters. The use of the measure is demonstrated with examples of implementation of linear-phase IIR systems and estimation of transients in variable IIR filters     

Toward Next-Generation Digital Keyboard Instruments

In this article, alternative approaches to digital keyboard instrument synthesis are looked into. Physics-based sound synthesis, which aims at generating natural-sounding musical instrument tones algorithmically without using a large sample database, is a promising approach. It would provide high-quality music synthesis to systems that cannot afford a large memory, such as mobile phones and portable electronic games. The realistic parametric synthesis of musical instrument sounds is still a challenge, but physical modeling techniques introduced during the last few decades can help to solve it. Recently, the first commercial products have been introduced, for example, by Pianoteq. Three keyboard instruments, the clavichord, the harpsichord, and the grand piano, are focused on here. The sound production principles and acoustics of these instruments are first discussed. Then, the previous parametric synthesis algorithms developed for these instruments are reviewed. The remaining part of this article concentrates on new signal processing methods for parametric synthesis of the piano     

Milk type during mixed feeding: contribution to serum cholesterol ester fatty acids in late infancy

OBJECTIVE: To evaluate the contribution of the type of milk on serum cholesterol ester fatty acids in infants receiving mixed feeding, we analyzed 3-day dietary records and serum cholesterol ester fatty acid composition of 397 seven-month-old infants. STUDY DESIGN: The infants received, in addition to solid food, only one type of milk: human milk (n = 218), a ready-to-use liquid formula (n = 139), a powdered formula (n = 33), or soy formula (n = 7). RESULTS: Mean fat intakes were low and varied from 28% to 31% of energy; the milks provided 43% to 64% of the fat. The mean polyunsaturated/saturated fat ratios of solid foods were from 0.52 to 0.63 and of milks from 0.20 to 0.45. Breast-fed infants' relative serum linoleic acid (18:2n-6) concentration was low (51.2%), whereas infants fed liquid formula had low serum oleic acid (18:1n-9) in accordance with low oleic acid content in that formula. The breast-fed infants had markedly higher serum concentrations of arachidonic acid (20:4n-6) and docosahexaenoic acid (22:6n-3) than the infants fed any of the formulas. CONCLUSION: The typical fatty acid patterns of breast- or formula-fed infants were still evident in 7-month-old infants who already received 60% to 70% of their energy from solid food. Marked differences were seen also in the relative concentrations of docosahexaenoic acid and arachidonic acid despite their small contribution in cholesterol esters.     

Antialiasing Oscillators in Subtractive Synthesis

In this article, oscillator algorithms for digital subtractive synthesis were reviewed. The algorithms were divided into three categories: bandlimited, quasi-bandlimited, and alias-reducing methods. In the first category, the most interesting methods are in practice those that utilize wavetable techniques. The second category consists of methods that low-pass-filter the underlying continuous-time signal prior to sampling. The optimization of the previously introduced BLIT and BLEP methods were considered as a filter design problem. A new technique called the PolyBLEP method was introduced as a variation of the BLEP method that does not require a table lookup but is based on a closed-form formula. In the PolyBLEP algorithm, an integrated polynomial interpolation function is used for acquiring samples to correct the transition region of the waveform. In the third category, the DPW oscillator algorithm generates an approximate sawtooth waveform that has reduced aliasing. This recently proposed method is probably the simplest useful technique for this purpose, because only the trivial sawtooth is simpler, but it is practically useless due to its heavy aliasing. An alternative decimation filter was proposed for the DPW2X algorithm to suppress aliasing well in the frequency region where human hearing is most sensitive     

Synthesis of Hand Clapping Sounds

We present two physics-based analysis, synthesis, and control systems for synthesizing hand clapping sounds. They both rely on the separation of the sound synthesis and event generation, and both are capable of producing individual hand-claps, or mimicking the asynchronous/synchronized applause of a group of clappers. The synthesis models consist of resonator filters, whose coefficients are derived from experimental measurements. The difference between these systems is mainly in the statistical event generation. While the first system allows an efficient parametric synthesis of large audiences, as well as flocking and synchronization by simple rules, the second one provides parametric extensions for synthesis of various clapping styles and enhanced control strategies. The synthesis and the control models of both systems are implemented as software running in real time at the audio sample rate, and they are available for download at at http://ccrma-www.stanford.edu/software/stk and http://www.acoustics.hut.fi/go/clapd     

Suppression of transients in variable recursive digital filterswith a novel and efficient cancellation method

A new method for suppressing transients in recursive infinite impulse response (IIR) digital filters is proposed. The technique is based on modifying the state (delay) variables of the filter when coefficients are changed so that the filter enters a new state smoothly without transient attacks, as originally proposed by Zetterberg and Zhang (1988). In this correspondence, we modify the Zetterberg-Zhang algorithm to render it feasible for efficient implementation. We define a mean square error (MSE) measure for transients and determine the optimal transient suppressor to cancel the transients down to a desired level at the minimum complexity of implementation. The application of the method to all-pole and direct-form II (DF II) IIR filter sections is studied in detail. Time-varying recursive filtering with transient elimination is illustrated for tunable fractional delay filters and variable-bandwidth lowpass filters     

Efficient tunable IIR and allpass filter structures

A new recursive filter structure is proposed which can be controlled on-line using a single parameter. The structure can be used for interpolation in timing synchronisation of digital communications receivers. The technique is illustrated with an example of the implementation of a tunable fractional delay allpass filter using the Thiran design technique     

Splitting the unit delay [FIR/all pass filters design]

A fractional delay filter is a device for bandlimited interpolation between samples. It finds applications in numerous fields of signal processing, including communications, array processing, speech processing, and music technology. We present a comprehensive review of FIR and allpass filter design techniques for bandlimited approximation of a fractional digital delay. Emphasis is on simple and efficient methods that are well suited for fast coefficient update or continuous control of the delay value. Various new approaches are proposed and several examples are provided to illustrate the performance of the methods. We also discuss the implementation complexity of the algorithms. We focus on four applications where fractional delay filters are needed: synchronization of digital modems, incommensurate sampling rate conversion, high-resolution pitch prediction, and sound synthesis of musical instruments