SUBBAND CODING Essay Example | Topics and Well Written Essays - 1000 words

SUBBAND CODING - Essay Example Index terms-- template, markup, discount I. INTRODUCTION The degree to which the bit rate can be reduced or compressed without impairing the quality of the decoded signal strongly determines the efficiency of an encoding technique. Typically, speech and audio signals have a high degree of redundancy which may be exploited to reduce the bit rate. In addition, the human auditory system possesses certain properties which may be useful in reducing the bit rate without compromising the quality of the decoded signal. 1 To take advantage of the aforementioned properties, a variety of techniques have been developed to efficiently represent speech and audio signals in digital form for either transmission or storage purposes. Since two different sub bands in each signal exist, the lower-frequency band and high-frequency band, and most of the energy in the signal is contained in the lower frequencies, it is possible to encode the lower-frequency band with more bits than the high-frequency band. Sub-band coding is a powerful approach where a speech or audio signal is broken down into several frequency bands and each band is digitally encoded separately. 2 II. Sub-Band coding implementation Figure 1 shows the basic configuration of the two- band sub-band design. The input signal represented as xi (n) is divided into two equally spaced frequency bands by low pass filter and high pass filter, represented as H1 and H2 respectively. After deviation, the sampling rate of each sub-band signal is reduced by a factor of 2. For instance, if the sampling rate for the input signal is Fs, then the sampling rate for each of the sub band after the deviation will be Fs/2. Reducing the signal by a factor of 2 follows every after frequency subdivision. By allocating a different number of bits per sample to the signal in the sub-bands, a reduction in the bit rate of the digitalized speech signal can be achieved. Meanwhile, the receiver converts the sub-band signals back to their original sam pling rate by using the similar low pass and high pass filters as the input. The sum of two sub-band signals represented as xo (n) is the reconstructed signal of the input signal (Figure 1). Figure 1 After the input signal has been decomposed into two sub-band signals, each signal is then passed through the Quantizers. The resulting signals are represented as QL and QH in the figure above. Filter design is particularly important in achieving good performance in sub-band coding.2 III. implementing the system using sub-band coding A. Creating a New Paper For writing a paper from scratch using the IEEETRAN.DOT template, or creating an empty document in the template for cutting and pasting text from an existing file in some non-Word format, the following steps should be followed: 1. Copy IEEETRAN.DOT into the template’s directory, e.g., C:\MSoffice\Templates, so that it will be available from within Word. 2. Open Microsoft Word. 3. In the File menu, select New option. In the New dialog, select IEEETRAN.DOT. 4. IEEETRAN.DOT's startup macro will pop up a dialog box requesting to type in text for several of the paper’s elements. Some information may be typed in the box if all the information being asked is not yet available. In fact, the default text can be left in place for the meantime. These elements can always be edited later. Note that the macro will not be repeated when the user re-opens the document. The cursor should now be positioned near the top of the paper, indicating that the program is now ready to begin