1. Field of the Invention
This invention relates to voice signal processing techniques, and more particularly, to a voice detection method and apparatus which can detect whether a received signal is a voice signal or a background noise. In the invention, the voice detection does not to perform multiplications and divisions so that the hardware complexity and cost for implementation can be significantly reduced.
2. Description of Related Art
Voice detection is a signal processing technique used to determine whether a received signal is a voice signal or a background noise and if a voice signal is detected, the begin point and the end point of the voice signal is determined. One conventional method to achieve this purpose is to compare the mean and standard deviation of the energy of the received signal and also the zero-crossing rate of the same with preset values. The comparison result then indicates whether the received signal is a voice signal or a background noise; and if a voice signal, the begin point and end point of the voice signal are also determined.
Fundamentally, the energy of a voice signal can be obtained from the following equation: ##EQU1##
where
E(i) is the energy of the (i)th frame of the digitized voice signal; PA1 SQRT is a square-root operator; PA1 M is the total number of sampling points in each frame; and PA1 X(n) is the digitized data from the (n)th sampling point in the (i)th frame.
The foregoing equation is too complex to perform. The following less complex equation can be used instead to compute for E(i): ##EQU2##
Therefore, it requires M-1 additions and one division to perform the operation of Eq. (A2) to obtain the value of E(i). In the case of using a sampling frequency of 8 kHz (sampling period=0.125 ms) to digitize the voice signal into 8-bit digital signal, then M=160 for a frame length of 20 ms, which requires 159 additions and one division to obtain the value of E(i). The hardware needed to perform this operation is therefore quite complex. Moreover, in order to prevent overflow, an accumulator of a large bit length should be used. This further increase the complexity of the hardware needed to implement the conventional voice detection method.
To make the products of voice detection apparatuses more competitive on the market, the manufacturing cost should be down. One conventional voice detection method and apparatus utilizes an accumulator of a large bit length and a preemphasis circuit that involves multiplication operations. This voice detection apparatus is therefore quite complex in hardware architecture and thus high in manufacturing cost. Another conventional voice detection method and apparatus utilizes a cascaded series of registers to implement the large bit-length accumulator. One drawback to this scheme, however, is that it would cause a degrade to the system performance and throughput and an increased degree of complexity in programming. There exists, therefore, a need for a new voice detection method and apparatus, which can be implemented with less complex hardware circuitry.