If you have activated the hold function correctly, you should see the ‘Tap/ Hold’ button stay solid blue. If this is not the case, simply hold this button down until it is. If the button is solidly lit and yet the hold function doesn’t seem to be working, this may be an issue with:

-    The firmware. Go to the Deepmind 12D product page and download the latest firmware updater for the device, and try updating the firmware.
-    The keyboard/ MIDI device that you are sending MIDI into the Deepmind from. The keyboard may be sending an ‘all notes off’ message when all keys are released, which could be overriding the hold function. If possible, try connecting a different MIDI keyboard to the Deepmind 12D, or see if there is such a function on the keyboard and whether this can be disabled.