In this paper we investigate several methods to estimate the signal in the lost packet of MP3 audio using side information. Our methods are based on a packet loss concealment method using sign correction proposed by Suzuki et al. Suzuki's method uses sign of lower MDCT coefficients as redundant information, and the sign information is used when estimating the MDCT coefficients of the lost packet. In this paper, we propose a new method to use the same side information as Suzuki's method. Our method is a combination of one-bit quantization and sign correction, which is proved to be better than sign correction for improving correlation between the original signal and the restored signal. The experimental result shows that the proposed method outperforms the sign correction method. Next, we investigated several methods to use two bits for correcting one coefficient. From the experimental results, the combination of two-bit correction and one-bit correction gave the best result.