INTRODUCTION This Item provides a computerised method for estimating exhaust noise spectra in one-third octave bands from a given database. The procedure is an interpolation/extrapolation routine which@ because of the variables considered@ is particularly applicable to estimating the noise from a coaxial jet. Because the procedure is essentially one of interpolation of noise spectra@ the particular form of the database need not be restricted to data for an isolated coaxial jet@ but could be of a more complex nature (such as a database obtained from an engine including combustion noise@ shock noise@ flight and installation effects and from alternative engine geometries). In order to be able to illustrate the use of the method@ an example database is provided for the case of far-field@ coaxial@ subsonic jet mixing noise from stationary@ coplanar conical nozzles. The noise estimation method has been validated for use with a provided database and also with another database using a different third independent variable. An advantage of this method over other approaches is the ease with which the database may be altered: new data can be added as they become available without modification to the computing procedure. A simple introduction to jet mixing noise@ together with other types of gas turbine exhaust noise@ is given in Item No. 74001 (Reference 3). A computer-based estimation procedure for single-stream jet noise including a database for far-field jet mixing noise from circular nozzles for a stationary source is given in Item No. 85018 (Reference 5). Two different computer programs are provided@ one in FORTRAN 77 programming language and the other in Microsoft BASIC. Using three independent variables@ a minimum of ten points is required in the database.