To solve daily problems, sometimes information needs to be accessible digitally or online by authorized parties. However, accessing some information may need secure data transmission. This reliable process can be achieved by using data security techniques to protect the transmitted information, such as cryptography or steganography. As part of data hiding methods, steganography works by hiding private information inside other public data, mainly multimedia data, in plain sight. Nevertheless, there are some main concerns regarding previous research, such as the similarity level and hiding capacity of the respective audio file. In this research, private information is embedded into an audio file as cover data so it can be retrieved later by the receiver without any suspicion of other parties. Therefore, this research focuses on providing flexibility in the embedding capacity of cover data by using an interpolation-based approach as the core sampling technique and then enhancing the similarity level by adding bit threshold values to evenly distribute hiding capacity on each sample as even as possible. Experimental results show that this proposed method can achieve an average similarity level of 103.56 dB on 100 Kb private data to an average of 93.95 dB on 300 Kb private data. It is better than some existing studies.