Abstract: The proposed technology generally relates the field of data transmission, in particular it relates to decoding an encoded data signal received at an audio interface of a portable electronic device, wherein the encoded data signal is encoded with an encoding scheme having an adjustable encoder clock frequency. The proposed method comprises pre-processing the received encoded data signal; scanning the received encoded data signal for a known start sequence and when a known start sequence is successfully detected then calculating an actual frequency based on the detected start sequence; interpreting, a data block succeeding the start sequence using the assessed actual frequency; and assessing whether to request adjustment of the adjustable encoder clock frequency based on the scanning and/or the interpretation. The proposed technology relates to a method performed in a portable communications device well as a corresponding device and computer program.