The way the expression pedal works on the X-Station is that you can assign it to any MIDI message you like in synth mode. This allows you to control any X-Station synth parameter using the Expression pedal by assigning it to the corresponding CC or NRPN message. The MIDI Control data for the X-Station can be found in the 'X-Station MIDI Implementation' pdf, available to download from here. As an example, to assign the expression pedal to filter cutoff do the following:
1. Look up which CC number filter cutoff is mapped to in the 'X-Station MIDI Implementation' pdf - it is CC105.
2. Put the X-Station into synth mode and press the 'template edit' button to enter edit mode.
3. Operate the expression pedal to bring up its settings and make sure it has the following set:
Control Type: CC
Control Num: 105
Low Value: 0
High Value: 127
4. Press 'write' twice whilst still in edit mode to save the settings and then press 'play/synth' to return to play mode.
The expression pedal will now control filter cutoff regardless of what synth patch you select because the expression pedal settings are saved with the synth mode template, which is recalled every time you switch into synth mode.
You may want the expression pedal to control a different parameter for each synth patch. If this is the case then you will need to assign the expression pedal, as described above, to one of the CCs which can be assigned to different parameters on the X-Station. These are:
CC1 - Mod Wheel
CC2 - Breath [NOTE: CC11 is the standard CC number for expression but it is mappped to the breath control settings on the X-Station. You can assign the pedal to CC11 and this will be equivalent to CC2 - you still use the AT/BR menu to assign it so it makes no difference whether you choose CC2 or CC11]
If you assign the expression pedal to CC1 then you can set what synth parameter it controls in the 'Wheels' menu. If you assign the expression pedal to CC2/CC11 then you can set what synth parameter it controls in the 'AT/BR' menu. If you assign the expression pedal to CC1 then it will have the same effect as the mod wheel.
When you set how much the pedal controls a parameter in the 'Wheels' or 'AT/BR' menus, you will find that the settings have a range of -64 to +63. The value you set will be the amount by which the pedal will change the parameter from its current value. Lets say you assign the pedal to output volume and set this to +63. If the current volume output setting is 25 then when the pedal is up the output volume level will be 25. When the pedal is down the output volume level will be 25+63=88. Thus the pedal will vary the volume between 25 and 88.
Now lets say you assign the pedal to output volume and set this to -52. If the current volume output setting is 127 then when the pedal is up the output volume level will be 127. When the pedal is down the output volume level will be 127-52=75. Thus the pedal will vary the volume between 127 and 75 (note the action will be inverted!).
Remember that the 'Wheels' or 'AT/BR' menu settings are saved with each patch. Thus if you change them you must write the patch to save the settings.