Entries Tagged 'Technology' ↓

A set of instructions that are used to peform arithmetic operstions on small groups or floating point numbers is provided. Single instruction multiple data instructions or SIMD instructions are useful for vector and matrix calculations in scienific applications. In intel terminology these instructions are called sreaming SIMD  extension instructions. They handle compound operands that are 128 bits long each consisting of four operands. Add and multiply are two of the most basic instructions provided in this group. They operate on the four corresponding pairs of 32-bit operands in the 128 bit compound source and destination operands and place the four induvidual results in the 128 bit destination location.

A two dimensional graphic or video image can be represented by an array of a large number of sampled image points. The color and brightness of each point, called a picyure element or a pixelcan be encoded into an 8-bit data item. Processing of such data has two main characteristics. The first is that manipulations of induvidual pixels often involve very simple arithmetic or logic operations . the second is that very high computational rates may be needed for some real time display applications. The same characteristics apply to sampled audio signals or speech processing, where a sequence of signed numbers represents samples of a continuous analog signal taken at periodic intervals. Through this application processing efficiency is achieved if the induvidual data items, which are usually bytes or 16 bit words are a\packed into smal groups that can be processed in parallel.

There are computers wth just one processor. Large computer systems may contain a number of processor units, in which case they are called multiprocessor systems. These systems either execute a number of different application tasks in parallel. or they execute subtasks of a large single task in parallel. All processors usually have access to all the memory in such systems, and the term shared memory multiprocessor systems is often used to make this clear. The high performance of these systems comes with much increased complexity and cost. In addition to multiprocessors and memory units, cost is increased because of the need for more complex interconnection networks. In contrast to multiprocessor systems it is also possible to use an interconnected group of complete computers to achieve high total computational power. he computer normally have access only to their own memory units. When the task they are executing need to communicate data, they do so by exchanging messages over a communication network.

In cepstral analysis of speech, the basic parameters of speech are clearly displayed and isolated from one another, that is the low frequency coefficients in the spectrum correspond to the vocal tract and that of the high frequency respond to the excitation information.

In homorphic Vocoder, the cepstrum is computed once every 10-20 seconds. The vocal tract cepstral coefficients are separated from the excitation co-efficients by a linear filterring operation. It also involves multiplying the cepstral co-efficients by an appropriate window function.

The excitation together with the quantized cepstrum values are transmitted to the synthesizer. At synthesizer, the vocal tract cepstral co-efficients are Fourier transformed, exponentiated and inverse fourier transformed to produce the vocal tract impulse response. By convoluting the impulse response with voiced or unvoiced signals the original speech is reconstructed.

The channel vocoder consists of both an analyser and synthesizer. The analyzer consists of a number of bandpass filters with a particular impulse response. It is then followed by a full wave rectifier as well as a filter. The full wave rectifier as well as low pass filter act as an envelope detector. Inorder to represent proper details or excitation of the speech signal, a channel vocoder is required which has a voiced/unvoiced detector and pitch detector. The resulting information, together with the amplitude of the signal forms the representations for the speech signal. These parameters are sampled and quantized for transmission.

At the reciever, a wide band excitation source is generated using voiced or unvoiced signal. The generator is used to switch a random voice or a pulse generator, with the fundamental frequency of the pulse generator being controlled by the pitch signal.