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LMK4+ User's Guide Page 20

APPENDIX A:

Explanation of the velocity-response curves and aftertouch curves.

When defining the parameters of the keyboard zones one can select among 64 velocity-response

curves and 8 aftertouch curves. In the following paragraph the reasons for this feature shall be discussed briefly.

The special MIDI-chip used inside the LMK2 to poll the key-contacts uses the time difference required by the

switch-contact to derive the velocity response (or dynamics-value). The relationship between measured time

difference and velocity is one of inverse proportion, i.e.doubling the time causes the velocity-response to be

halved. However, this is not the response one is used to from a piano. Thus the option of adjusting the keyboard's

velocity-response via response curves was created.

In the case of non-adjusted velocity-response (Curve 1) most people feel that the high values start too early and

that there is insufficient resolution in the lower range. There are several tables which more or less compensate for

this. The higher the number of the table (2...8) the more the velocity-response is moved upward, i.e. the harder

one must press the keys to obtain a given velocity-response. Tables 9...12 represent alternative velocity-response

curves, i.e. the dynamics rise even faster than in the inverse proportional curves. Tables 13...28 contain various

linear, logarithmic and exponential characteristic curves with start- or end-response. Table 16, for example, sends

a response value of at least 16. However, the rise of the response starts only at minimum key-pressure and ends

at a maximum value of 100.

Tables 29 and 30 contain reversed characteristic-curves, i.e. the velocity-response values decrease as the keys

are pressed harder. This seemingly illogical feature can be used for key-pressure-controlled blend-over effects

("Crossfade"). For this application one expander (or sound) is controlled with a 'normal' curve (1...28), another with

with a reversed curve (29 or 30). This is done by defining the same UPPER/LOWER key-values for two different

keyboard zones, but using different velocity-response curves and MIDI-channels for those two zones. Depending

on how hard the keys are pressed one expander will now become louder, while the other expander will

simultaneously become more quiet. The velocity-response characteristics will to some extent also depend on the

type of expander being used, since different instruments have different characteristics.

The velocity response curves 33-64 are identical to the curves 1-32 with one little exception. If a key is pressed

very slow the curves 1-32 produce a small velocity value (normally 1) whereas the curves 33-64 will send a

velocity value of 0 (this is defined as note off). The main reason for the curves 33-64 is that many expanders

produce an audible sound if they receive a note on event with velocity 1. But this is not the behaviour of a real

piano. A real piano will produce no sound in this case. So if you want to achieve the behaviour of a real piano you

have to select one of the velocity response curves 33-64 rather than 1-32. Therefore the curves 33-64 are called

"Piano Mode velocity response curves".

Velocity-response is to some extent also dependant upon the expander being used. There are significant

differences in the characteristics of different expanders. Some expanders also include various velocity-response

curves of their own. The 32 (64) curves included with the LMK4+ generally permit sufficiently good adjustment of

the velocity-response characteristics.

The LMK4+ also provides 8 aftertouch curves. In general, the same comments apply to these as to the velocity-

response curves. Curve 1 is linear. In curves 2...4 the high aftertouch values appear earlier, meaning that the

lower range of the aftertouch is more sensitive. Curves 5 and 6 have a minimum (5) and a maximum value (6),

repectively, for the aftertouch characteristic. Curve 8 is an inverted function, i.e. the aftertouch value decreases

with increasing pressure on the keys.

Graphical representations of the various curves can be found on the next page.

1 2 ... 15 16 17 18 19 20 21 22 23 24

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