Apologies, the response was mainly for the original poster ayang02 and the other poster using the default midi tools in macOS. And the ‘isolation’ in galvanic isolation is not isolation from noise but isolation of electrical current via a magnetic field in a transformer. if you are lucky it will give you maybe 40 or 50db noise attentuation across a certain frequency range. Low level noise in the signal will get transferred just like the signal is transferred, some high frequency noise is attenuated and other high frequency noise capacitatively couples across the windings. The better USB decrapifiers will do a lot better than this. There are many many fantastical assumptions about galvanic isolation on forums such as this and I think the misinterpretation of the word isolation Is where it comes from.