Low frequency bandwidth limitation is a common problem faced by miniature speakers and highly-directional speakers that have relatively high cut-off frequency. As such, low frequencies cannot be effectively reproduced. One of the current methods in addressing this problem is to employ psychoacoustic signal processing based on the “missing fundamental phenomenon”. Nonlinear device is generally used to induce virtual pitch that enhances the low frequency perception. However, some of the difficulties in using nonlinear device include the need of precise adjustment of harmonics' magnitudes, harmonic order and its decay rate to achieve good perceived bass. In this paper, we propose two techniques on synthesis of polynomial-based nonlinear device and harmonic shifting by modulation in an attempt to overcome these difficulties. Real-Time implementation and listening tests were conducted to verify the effectiveness of the proposed algorithm.