Fundamentals of digital audio communication

Audio information communication is an important task in multimedia. Sound is a form of longitudinal wave motion and its amplitude changes with time. The first step in digitization of audio signal is sampling where measurements are taken at evenly spaced intervals. The rate at which sampling is performed is called sampling frequency. For audio digitization, sampling rates ranges from 8KHz to 48 KHz. For better results, we follow Nyquist rate. Here sampling rate is maintained at a level which is equal to twice the maximum frequency content in the signal. Other important terms in this category are signal to noise ratio, signal to quantization noise ratio, linear and non linear quantization, audio quality versus data rate, audio filtering, synthetic sounds, coding of audio, pulse code modulation, differential coding, lossless predictive coding etc.

Gears

To transmit rotary motion between two shafts at a constant speed ratio, gears are used. The different methods used for the manufacture of gear teeth are shell molding, sand casting, die casting, centrifugal casting, permanent-mold casting and investment casting. Powder metallurgy method can also be employed here. Cutting of gear teeth can be done by milling. Shaping and Hobbing are the two methods of generating gear teeth. After cutting, for surface finish of gear teeth many processes are carried out namely grinding, lapping, shaving, burnishing etc. There are two main categories in gears. They are spur gear and helical gear. Spur gear is preferred when transmission of rotary motion is intended between parallel shafts. When loads are heavy, helical gears are preferred. Double helical gears are called Herringbone gears. This design got the importance due to one drawback of single helical gear. The drawback is that the axial thrust loads is to be accounted in the design of bearings. Some other types of gears are crossed-axis helical gears, bevel gears, straight-tooth bevel gears, crown and face gears, spiral bevel gears and worm gears.