So now all is revealed.
A - Genos
B - 970
C - CVP 605
D - Tyros 5
Some got some right, I think one or two got them all correct. Not sure of they have very discerning hearing or if it was blind luck, law of averages!
But most did not and an interesting point for me was how several rated B, the lowest cost keyboard on the list.
The main feature of the comparison was not the differences, but that it was so little. And that is even when you are trying hard to hear differences, not just listening to a performance. Most people were probably not even listening to the music, just focussing on the sound - and it was still hard.
But I am not saying there is no difference. I am sure that with a more technical test the differences might be more obvious, but they are really small at the level where it matters - when played normally. Certainly as I have said on this forum many times, the piano voice on even the much older arrangers like the PSR 3k, -the first model I had - was good enough. Put simply, no listener is going like or dislike what they hear because of the model or piano voice. it's what is played that matters.
So why do so many people think the piano voice on Yamaha arrangers is poor?
I believe it is because of how they are mostly used by arranger players, - single note melody line over full accompaniment and they feel like they would like a much richer sound. Yamaha could probably do that, and there have been many modified voices posted that achieve this. But then it may not sound like a piano when fully played as a piano.
I hope some of you found this an interesting exercise.
Thanks again to Toril for her help, and thanks to everyone who took the time to listen to the samples.
Mike