Units - Lexicon MPX 1 V1.10 - MIDI IMPLEMENTATION DETAILS Midi Implementation Manual

MPX 1 V1.10 MIDI Implementation Details Lexicon

Units

While most parameters in the MPX 1 use a single form of measurement, there are some that can be
measured in 2 or more unit types. The LFO's Rate parameter, for instance, can be adjusted in Hz or in
a ratio of the cycles per second. Another example is the delay time parameters which can be set for
milliseconds, a ratio of the number of echoes per beat, in meters or in feet.
When a parameter can be set using different units, the Parameter Description will include additional
minimum and maximum values as well as display units for these unit types. The currently selected
units"are defined in two ways — both of which are "options" to the parameter. The most straightforward
method uses a single byte option parameter which contains the currently selected units. In this case, the
actual data is transmitted with the parameter data as an additional byte (the Parameter Data message
packet for a one byte parameter with a units option would be sent with two bytes — the actual parameter
data and the option data). In this case, the second byte (the option data) would be read first to determine
the unit type. This is the method used for delay parameters.
The other method, typically used for Rate parameters, uses the MSB of the parameter data itself to
determine the units to use. In these cases the MSB is stripped off the parameter before it is used (for
display etc). In these cases, the "number of bytes" field in the Parameter Description for the option
parameter is 0.
Though the MSB method is used on all Rate parameters, the separate byte method is preferred.
Note that, while the Delay "Time" parameter can be set for "echos:beat" much like the Rate parameters
have "cycles:beat", the option value which defines the mode is a separate byte. The Rate parameters use
the MSB of the parameter value itself.
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