In order to detect a specific codec sequence being used, a signal that is based on a codec sequence is analyzed. The signal is analyzed to determine if there is a pattern in the signal. A pattern of a codec sequence can be a unique pattern of frames, frequencies and/or frequency ranges that are generated based on a specific codec sequence. The pattern is compared to one or more previously stored patterns of codec sequences to see if there is a match. If there is a match, an event is generated. For example, if a known codec sequence that has a poor signal quality is determined to be in use for a voice call, the parties may be notified that the call is likely to be a low quality voice call.