Are notes sounding louder or quieter than you'd expect based on how you've hit the key? For example, hitting a key as hard as you can but you aren't getting maximum (127) velocity, or velocity response seems inconsistent? There are a couple of methods for correcting this.
The first important step is to update to the latest firmware.
After that, any velocity issues you might be experiencing can be solved by calibrating the problem keys. Learn how to calibrate your keys here.
Did You Know? You can avoid recalibrating your entire keyboard by simply not touching the keys you're happy with during the calibration process. If there's only a few keys that are behaving incorrectly, go ahead and only calibrate those, and click the green button to save your work. Any keys that remained white will retain their existing calibration data.
