Sound bandwidth

The degree of attenuation at the critical frequency can be very large, but this type of silencer has a very narrow bandwidth. This device may be suitable when the machine being dealt with emits sound predominantly of a single wavelength. Lining the chamber with absorbers can expand the absorber bandwidth of a Helmholtz resonator, but this has the effect of reducing the efficiency. The perforated absorber, which forms the basis of many acoustic enclosures and silencers, is a development of the resonator principle. 

As stated previously, packing the chamber with an absorber may broaden the bandwidth, but this lowers efficiency. It may be overcome by using multiple absorbers in the sound path, and placing a perforated sheet some distance away from the rigid outer wall of the enclosure and filling the cavity with absorber can do this. It is not necessary to use cross walls between the chambers so formed. In this case the equation becomes ... 

In percussive sounds, such as a bell, gong, drum and other nonperiodic sounds, spectral components are typically aharmonic and can be simulated by forming an irrational relation between ooc and b)m (e.g., (Om = /2C0c). In addition, the envelope is characterized by a sharp (almost instantaneous) attack and rapid decay, and the bandwidth moves from wide to narrow. Bell-like sounds, for example, can be made by making the modulation index proportional to an amplitude envelope which has exponential decay. For a drum-like sound, the envelope decay is even more rapid than the bell, and also has a quick overshoot giving a reduced initial bandwidth, followed by a widening and then narrowing of the bandwidth. 

In Chowning s original work [Chowning, 1973], he explored three different classes of musical signals brass tones, woodwind tones, and percussive-like sounds. An important characteristic of these musical sounds, in addition to their spectral composition, is the amplitude envelope of the sound and its relation to its instantaneous bandwidth. 

Both these methods are described with the word noise, but in the first the noise has nothing to do with sound it refers to noise in the sense one meets the term in electronics. In electrochemistry, it refers to the random variation of the electrode potential, which has an order of magnitude of 10-4 V and a bandwidth of 1 Hz. 

It may sound like a paradox, but currently, in optimizing for a parallel computer most of the effort should be spent on making sure that the individual node performance is as good as possible. This is a consequence of the power of the individual node compared to the network latency and bandwidth. In short, the current parallel machines are of large grain type. The parallel algorithm used should make every effort to communicate as seldom as possible. For a best performance it often means that a particular calculated value, needed on several nodes, can actually be recalculated more quickly on each node, compared to communicating it to the nodes where it is needed. This is the parallel form of the classic optimization trade-off between memory and CPU cycles. 

For certain crystal cuts the motion is of the thickness-shear type. Since the motion at the crystal surface is then in the surface plane, these modes do not emit longitudinal sound (or at least not very much of it). The weak acoustic coupling to the environment increases the Q factor of the resonances to rather exceptional levels. The bandwidth is orders of magnitude smaller than the resonance frequency, which greatly simplifies the data analysis. 

The frequency response of the system is a high-pass filter, since, for tor 1, Vo(ift))/X] (io)) = E/xo, which is a constant. However, the response drops off for low frequencies, and it is zero when at = 0. This frequency response is sufficient for a microphone that does not measure sound pressures at frequencies below 20 Hz. The input impedance of the read-out device must be high (10 MS2 or higher) in order to achieve a required low-frequency bandwidth. Capacitance sensors are not suitable for measuring most physiological signals because the frequency spectra of these signals have dominant low-frequency components. 

Acoustical properties of soybeans can be used to help distinguish between healthy and diseased soybeans. Misra et al. (1990) measured acoustic properties of soybeans by transmitting sound waves through soybeans using acoustic transmission and by an impact force method. In the impact force method, a seed is dropped on an acoustic transducer creating an impulse wave. The acoustic transmission method was slow but was able to predict the mass of individual soybeans. The impact force method showed that diseased soybeans had a narrower bandwidth than healthy soybeans. Soybeans with wrinkled surfaces and diseased and damaged soybeans were detected from healthy soybeans based on wide variations at low frequencies. 

Similar to the optical analogy, the problem is solved by acoustic quarterwave matching layers (Fig. 10). Silica aerogels with densities of around 300 kg/m have the ideal acoustic impedance to match a piezoelectric transducer to air [77]. In addition, they exhibit rather low attenuation, as opposed to many porous, polymer materials used for this purpose until now. An increase in sound transmittance by more than 30 dB was achieved in a relatively simple arrangement without optimization. More elaborate designs, eventually including multiple layers combining different materials, will probably result in transducer systems optimized with respect to output power, sensitivity, and bandwidth. 

Related to SDIF, but on the control side, is Open Sound Control (OSC). Open sound control allows for networked, extended precision, object oriented control of synthesis and processing algorithms over high-bandwidth TCP/IP, FireWire, and other high bandwidth protocols. 

Figure 12.14 Examples of spectra calculated from LP coefficients for a range of different sounds. Note how all the spectra are absent from any harmonic influence, and that all seem to describe the spectral envelope of the speech. Note the characteristic formant patterns and roll-off for all vowels, and compare this with the spectra for /s/. The same vowel is present in both examples (e) and (f). Note that while the formant positions occur in the same positions in both, the amphtudes and bandwidths are quite different, especially in the fourth formant, which is barely noticeable in example (e).

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