As the popularity of electric stringed instruments is increasing, there is a need for developing new processing unit for these instruments instead of using music synthesis, which has difficulty in retaining the playing styles. This research is to design and implement a real-time digital resonator for electric cello to reproduce a musical sound like acoustic cello by using TMS320C31 development board. The digital resonator consists of robust fundamental frequency estimation (FFE) and transformation filter. The digital resonator first determines the musical note by estimating the fundamental frequency of the picked-up signal and then processes the signal with the filter associated with the note being detected. An FFE algorithm and a modified time-domain least-square (MTLS) finite impulse response (FIR) filter design method for transformation filter were developed. The FFE algorithm is based on least-square error (LSE) fitting and harmonic structure hypothesis testing. Evaluations show that the FFE algorithm can cope with the problems of low frequency resolution and complicated harmonic structure for short window size. With the same order of computational complexity, the algorithm outperforms the other FFE algorithms. It also has a good frequency tracking capability and can operate in real time. In the MTLS filter design method, a new criterion, total harmonic gain to noise ratio, in addition to the least-square (LS) criterion is introduced. Compared to the Time-domain LS FIR filter design method, MTLS offers a better solution having low noise gain and small time-domain distortion. The digital resonator has been implemented on a DSP board based on TMS320C31 with transparent delay time. In addition to objective evaluations, perceptual evaluations for the digital resonator were conducted. Results indicate that the digital resonator not only improves the sound quality of the electric cello but also produces targeted acoustic cello sounds with playing styles retained. The digital resonator introduced in this thesis is a general design, not exclusively to cello, that enables one to improve the sound quality of any electric stringed instrument.