what does midi "expression" controller do?

Discussion in 'Converters / Interfaces' started by patrickh, Oct 4, 2005.

  1. patrickh

    patrickh Guest

    Hi. I'm wondering if somebody can explain to me what the "expression" controller (#11) does, and whether it really does anything different from the volume controller (#7). As far as I can tell, raising or lowering the "expression" value just changes the volume.

  2. Kev

    Kev Well-Known Member

    Nov 13, 2001
    All CC's
    continuous controllers
    can only do things if the sound is programmed for a change.

    Volume is an obvious one and is very simple to explain.
    more controller = more volume.

    Pitch is also very obvious
    more controller = higher pitch (for example)

    others can be very subtle
    they can seem like EQ changes ... moreor less reverb or delay ... change the delay times or repeats.

    Then comes the dynamic sound changes that can be hard to explain.
    Hit the keyboard hard and you get a sound that is louder BUT also it may have a change in tone.
    A CC can be made to induce this sound with more or less strength in the finger or stick hit.

    this is where the EXPRESSION comes in. Breath controllers are often in this expression area.

    Poor explaination I know
    often these things need to be touched and listened to ... to get the idea.
  3. patrickh

    patrickh Guest

    thanks Kev, but I know all that, and my question needs a more specific answer. Anybody out there who can help?

  4. freaky

    freaky Guest

    Interesting, I thought expression worked differently- until I did a little research and came up with this from the web:

    Number: 11 (coarse) 43 (fine)


    This is a percentage of Volume (ie, as set by Volume Controller). In other words, Expression divides the current volume into 16,384 steps (or 128 if 8-bit instead of 14-bit resolution is used). Volume Controller is used to set the overall volume of the entire musical part, whereas Expression is used for doing crescendos and decrescendos. By having both a master Volume and sub-Volume (ie, Expression), it makes possible adjusting the overall volume of a part without having to adjust every single MIDI message comprising a crescendo or decrescendo. When Expression is at 100% (ie, maximum or 0x3FFF), then the volume represents the true setting of Volume Controller. Lower values of Expression begin to subtract from the volume. When Expression is 0% (ie, 0x0000), then volume is off. When Expression is 50% (ie, 0x1FFF), then the volume is cut in half.

    If a MultiTimbral device, then each Part usually has its own Expression level.

    Value Range:

    14-bit coarse/fine resolution. 0x0000 to 0x3FFF where 0 is minimum effect.

    NOTE: Most all devices ignore the Fine adjust (#43) for Expression, and just implement Coarse adjust (#11) because 14-bit resolution isn't needed for this. In this case, maximum is 127, 50% is 64, and off is 0. So assume that a channel's volume is 100. After receiving an Expression Controller of value 64, the volume is reduced to 50 (ie, 50% of 100). After receiving another Expression of 127, the volume is restored to 100. Now, assume the volume is changed (via Volume Controller) to 80. After receiving an Expression Controller of value 64, the volume is reduced to 40 (ie, 50% of 80). After receiving another Expression of 127, the volume is restored to 80.
  5. patrickh

    patrickh Guest

    Thanks very much Freaky. That solves that question for me! (I had sort of come to the same conclusion, thinking about it after I posted the question. My guess was that that it allows you to put in small volume changes in a part, and still be able to adjust the overall volume in relation to the other parts using the main volume controller. But it's good to know for sure!).


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