Subband Coding of Speech Signals Using Decimation and Interpolation

In many practical applications of digital signal processing, such as telecommunication systems, one is faced with the problem of changing the sampling rate of a signal, either increasing it or decreasing it by some amount. In telecommunication systems, that transmit and receive different types of signals, there is a requirement to process the various signals at different rates commensurate with the corresponding bandwidths of the various signals. This paper addresses the problem of sampling rate conversion and multirate signal processing in the digital domain. A structure of a two-channel quadrature mirror filter with low pass filter, high pass filter, decimators and interpolators, is proposed to perform subband coding of speech signals in the digital domain. The proposed structure decomposes a signal into low frequency and high frequency components. The performance of the proposed structure is compared with the performance of the delta-modulation encoding systems. The results show that the proposed structure significantly reduces the error and achieves considerable performance improvement compared to delta-modulation encoding systems.