1. A system comprising: a gas turbine engine comprising a combustor and igniter configured to produce hot gas to propel an axial shaft; a dynamic pressure sensor mounted to detect acoustic frequencies in the combustor; and a processor in electrical communication with the dynamic pressure sensor, the processor configured to: receive from the dynamic pressure sensor first data that indicates signal changes in each of a plurality of time bins during operation of the igniter in the combustor; determine information characteristics of the first data in each of the plurality of time bins; determine a value of a similarity measure that indicates similarity of the information characteristics to target information characteristics; determine a condition of the igniter based on the value of the similarity measure; and output a remedial response for the igniter based on the condition of the igniter.