what is the difference in 3 and 4-level AWM Dynamic Stereo Sampling(yamaha digital pianos) quality ? is there a significant difference?
Ah, the key word is "significant". That depends. As your ear gets better and you learn what pianos sound like even "4" becomes a low number. That said Yamaha in the P95 does a surprisingly good job with just 1 layer. So number of layers does not tell the whole story
A beginner will likely not notice the difference between 1 and 4 layers because he plays all keys with the same force and at first is not to concerned with dynamics as it is hard enough to just play the correct notes in correct time.
But later you find a piano makes different sound when you play lightly, not just less loud but different. How many shades of different is determined by the number of layers.
It is more complex than that. Yamaha, in their better pianos, does not simply switch between the layers, they mix or bland two of them to get intermediate sounds. Some of their 3 layers pianos don't do this blending, the newer P155 blends with four layers. So you gain more then just one layer, they've added blending too. This level of detail does not show up in the specs, you have to listen to the piano.
Other things added like key-off samples and string resonance do show up in the specs and maybe might matter as much as the extra layer.
Going back to the P95 with it's one layer. Yamaha applies a filter to the sound of that one layer and the parameters of the filter depend on key velocity. This has the effect of making the sound change from mellow to bright as you play harder on the keys. It is not 100% realistic but works.
Bottom line is to not imply count layers as there is more going on.
Now to directly answer the question. I can tell a difference at the upper end between my P155 and other 3-layer Yamahas but can't tell much different if playing only mid range loudness, but I can deffinatly tell if I smak the key hard, the P155 has what I think of as a metalic sound to it, (Maybe there is a better word)
Anyone here undertand the physics? On a guitar if I play louder it means I pull harder in the string and it makes the pitch sharper during the attack phase of the note. I see the effect clearly on a chromatic tuner. maybe this happens on a piano?