I am facing a trouble implementing the fft and appreciate your advice. My data structured as follow: The data are retrieved from the share market for one day change in the share price. The time range from (11:00:00 to 15:00:00) this means 16200 Sec. In matlab its represented as serial so it will be from 0.4584 to 0.6458. Data are not sampled in fixed freqency. Price is sampled only when there is a change in price. For example ( it can be sampled in each second and sometimes in 30 Seconds interval).