In our SYNTH BASICS series or articles, we are working our way toward the subject of the control you have over the resulting sound via the available parameters. We've been discussing organs, and most recently piano, but will cover the types of control that you can implement using the various synthesis methods in upcoming articles.

Analog synthesis is the basic model upon which Sample-playback synthesizers are built. The basic OSCILLATOR (tone source), FILTER (tone modifier) and AMPLIFIER (loudness) paradigm is used in both systems. With analog you are often limited (if by budget alone) to the number of components you have available. Typical is one or two oscillators, a single Filter and Amplifier for all oscillators together... in the typical sample playback synth - you are not so limited, for example, in the Motif XF Voice you have as many as 8 oscillators each with its own complete set of synth components (not to mention effect routing, et al).

When you think about it, the sample engine has the ability to customize (to a ridiculous degree) the resulting sound you get... just because most users never avail themselves of this potential is a huge worry for synth manufacturers. Nothing could be more heartening to see is interest in customizing sounds. Even tweaking a few parameters can turn a Voice into something special!

Each of the Elements within your piano Voice has multiple Oscillators (tone sources) - each responsible for some portion of the whole sound. You will need to take a look inside this VOICE and see how the original programmer put this together (or you can learn from it and build your own from scratch). Some Elements may be responsible for responding only at a specific VELOCITY RANGE or KEY RANGE on the keyboard.

Typically, the main body of the piano (usually up to about G5 on the keyboard) is made from different samples than those above G5 - where the dampers of the acoustic piano end - the behavior of the top notes of a piano are markedly different from those with hammers and dampers. Often multiple velocity ranges are used throughout the main body of the instrument - each set of samples (called a "Waveform" in the Motif XF) are referenced by the Element on the OSCILLATOR page
Press [EDIT]
Press [1] to select Element 1 parameters
Press [F1] OSCILLATOR
Here the first Element is referencing a set of samples (Waveform) that is performing a role within that VOICE. You can SOLO it by pressing the [SOLO] button (or by muting the others). You will quickly discover that it is not played across the entire keyboard, nor probably is it sounded at all velocities... The settings are also found on this screen for NOTE LIMITs and VELOCITY LIMITs.

Explore the VOICEs Elements and their roles.

You want to concentrate on the AMPLIFIER screen found at [F4]
Here you will see the Envelope (the shape of how the Element comes in, what it does while it is in, and how it disappears) the AMP envelope is responsible for the loudness.

Of particular importance to your question is the Velocity Sensitivity as applied to the EG (Envelope Generator) Time. You can profoundly affect how the envelope shape changes as you increase velocity. (see page 81 in the REFERENCE MANUAL) "EG Time Vel Sens"

You may want to experiment with how Velocity of your Note-on event is applied to the "DECAY" portion of the Envelope. Changing the value negatively will reduce the speed at which it traverses this portion of the envelope. This particular parameter is an OFFSET - this means it is applying this change by adding/subtracting values as set for the DECAY 1 TIME and DECAY 2 TIME parameters (those responsible for what happens during the time you are holding a key). The DECAY 1 LEVEL is important because this is the level at which the sound falls after the attack. On a piano DECAY 2 LEVEL will always be 0 (Decay2Level actually describes a sound as a percussion sound, meaning that the sound will eventually die away completely. If Decay2Level is not 0, the sound will sustain indefinitely, as in forever, or you RELEASE the key).

If you cannot find the exact offset value that works, you can dig deeper and adjust the Decay parameters themselves (careful do not change Decay 2 Level). You will know when you cross from the real world into the science fiction world - it is a synthesizer so you can do outrageous things to envelopes and stuff. If you want to keep it real world (acoustic like) let your ears and sensibility be the final judge!

For a discussion of the envelope found in the Yamaha Synths please see this article:
Synth Basics: Sound Experiments

A couple of tips: In general, the harder you strike a key the brighter the timbre (handled by the Filter and FEG) but also the longer the sound lasts... so you must be careful to recognize how each Element contributes to the whole of the sound. There are likely Elements for low velocities, another for medium velocities and yet another for forte velocities... each with its own Amplifier and Amplitude EG

I highly recommend working with a single Element when experimenting with just what each parameter can influence. Working on someone else's 'sculpture' can be enlightening but also can be confusing if you are not aware of why they made certain decisions. Any way if you get stuck post back here.