Acoustic communication is transmission technology with sound and data by using speaker and microphone. In this paper, we propose a parallel acoustic communication system that is able to transmit text data in office environment using unused high frequency band in audio signal. So, we analyze the performance of acoustic communication. This system sends both sound in low frequency band and OFDM (orthogonal frequency division multiplexing) data in high frequency band at the same time. In the case of acoustic communication system, frequency offset is generated from speaker and microphone. Therefore, we compensate frequency offset and perform real experiment to ensure the good system performance.