Continuous positive airway pressure (CPAP) is a typical medical treatment for obstructive sleep apnea syndrome. Without using a small CPAP machine which are patented, we aim to design a new technique using microphone array for measuring respiratory sounds. Hence, it is necessary to obtain effective features of respiratory sounds such as, inspiration, expiration, and snoring in order to supply appropriate pressure depending on the respiratory conditions of patients. Furthermore, it is often difficult to measure only respiratory sounds separately from other environmental sounds by the use of CPAP machine operation, for example, blowing sound of subjects should be eliminated for CPAP machine. As the first step, short-time Fourier transform is applied then we can compare the sound features of inspiration and expiration observed by the microphones. Some different features can be observed in the time-frequency magnitude spectrogram. From these results, the feasibility of using inspiration and expiration features independently in a prospective detection technique.