If you want decent sound, be prepared to pay over a hundred quid for a decoder, sound file and decent speaker. I prefer Zimo sound decoders but a lot like ESU as well.
With all respect to the suggestions above, are you sure you really want this? It was an appalling racket, with some very unpleasant high frequency effects. If relatively accurately reproduced, unless you actively enjoy aural torment, I feel it will be turned off quite rapidly....Can anybody recommend the best sound to replicate 1980's HST...
They were OK for travelling in; but then the class91+ mk4 sets appeared and kicked them into the dust in all respects; so that's where my later BR designed express passenger train affections will ever reside.... dont we all miss the Valenta powered HST's ....