Click on the Engine Sounds tab. You'll see the following dialog.
The Sound TypeENG1_COMBUSTION is made up of 4 sound files mixed together. Each one is described by a Sound List entry. Click on the Preview Sound button, or double click on ENG1_COMBUSTION in the Sound Type list box to begin the Preview dialog. More technical info on Sound Types and Sound Lists can be found in the Sound Background section.
The Preview dialog shows us the 4 Sound List entries. Along with their names is the FS Sound Studio calculated Volume and Rate information for the current simulated RPM. The Volume Envelope graph displays the 4 Sound List's Volume envelopes, each in a different color. The Rate Envelope shows the corresponding Rate envelopes. The Sound Source box tells us a bit more about these sounds. In this example, we'll be listening to Internal sounds - sounds heard in the cockpit. (There are a number of Flag entries which can be set to associate the sounds with specific Engine events. Please see the Microsoft SDK for detailed information.)
Listening to the Mix
Press the PLAY button to hear the ENG1_COMBUSTION sound as you would in FS2002. Move the RPM slider to vary the simulated aircraft RPM. Note the change in sound. As the RPM slider moves, FS Sound Studio updates the Sound List entries to show each one's Volume and Rate for any given RPM. Click on the COMBUSTION.1.02 entry in the list box. The Line Color box under the Edit... button shows the color used in the graph for this particular entry.
Simulated Engine RPM
Move the RPM slider so that the simulated RPM is approximately 1275 RPM, as in the screenshot above. The cursor line displays the current simulated RPM exactly in the Volume envelopes. In this case, we can see that almost all of the sound being produced is a result of the COMBUSTION.1.02 sound. All the other entries have a calculated Volume of -100db, the minimum.
Turning Individual Sounds on or off
Click on the checkbox at the left edge of COMBUSTION.1.02. With the checkmark removed, FS Sound Studio will remove the entry from the preview mix. Move the RPM slider to hear the contribution made by the missing entry. When Finished, click on the checkbox to restore the sound. Adjust the RPM Value back to 1275RPM. Note that these checkboxes do not affect how the sounds are heard in FS2002.