It’s true bypass to ensure signal path integrity and when the tuner is engaged your output is muted. The EHX-2020 can be calibrated to a reference standard of 436 to 445Hz in 1 Hz steps so being able to tune to and play together with instruments that might not be at 440Hz is not a problem. It has a wide tuning range of B0-B7, plus three flat tuning modes so you can tune down ½ step, a whole step or a minor third. The compact, affordable EHX-2020 Chromatic Tuner Pedal comes with its own 9V DC Adapter. • MFSKU 2020TUNER • UPC 683274032023