Nice Piccys. Is the loco fitted with a Massoth pulse wheel sensor ?
No - but it definitely would be improved with one. For either the LS or the XLS decoder the sound is distinctly out of phase during the start up!
To get the sound more closely synchronised with the start, I tinkered with CV194 (trigger threshold for sound - digital), the starting voltage (CV2) and the acceleration time (CV3). It's easier if you've already reduced the top speed (CV5) to something realistic (>100) and suitably adjusted the mid speed (CV6) to around 30, to compliment the new top speed value (I run my locos 28 speed-steps, which. if that's your preference, should also be set in advance).
Slow speed running is improved if you increase CV61 (readjustment retard) from the curious Massoth default setting of 2 to something above 20 (the default shown in the tables).
That way I've found that I can get movement at the start to coincide with the starting sound and not lagging about half-a-dozen chuffs behind! Nevertheless I suspect pulse control from a wheel sensor is a better solution.