I downloaded the observation car in Train-sim.com library (obsrvcar.zip), and added the interior from the oebarcar (oepassview.s, .sd, and .ace). Changing the RotationLimit from 80 t0 180 gave me a view out on the observation platform, only because Microsoft/Kuju didn't make a rear view for the interior. Works for me. Anyway, I got a little irritated by the same piano tune looping over and over. I tried the Random modification posted here by Stuart, but never got random playback. So I decided to use the original file unmodified and made one large .wav file and rename it oe_pamb_piano1.wav. But before embarking on this, I thought I'd better ask here if anyone sees a problem with a large .wav file (maybe 10-20 minutes) other than wasted hard drive space? Also, would it be possible for the .sms file to trigger the CD drive? I could burn music to a CD in .wav format, and not have to waste the HD space. Or, could I trigger Windows Media Player (gee, wouldn't you think Microsoft would have thought of that) from the .sms file?
Not sure about the CD etc, but can advise the following. In the Global folder is a file called sound.cfg which lists various audio system settings. It seems that between the various levels of sound quality (ie ScalibilityGroups) the only difference is an allocation of memory. It seems that the highest (SG5) gets 30Mb. Don't know what this represents, but at a guess it's a memory allocation for storing the scripts (.sms files), their variables, and the .wav files. Hence I'd guess that if files get too large you can exceed this allocation. What happens then? Don't know. Maybe more disc accessing will occur (hence stuttering during the game) or MSTS locks up! However I have increased this memory allocation (doubled it) with success in the past.
Thanks for the reply. I didn't know what ScalabilityGroups was (were). I've been making new Sound Sources. If I see that too many of them are affecting frame rates, I might be able to adjust memory allocation, or would it be better move them to a different ScalabilityGroup?