You will need an adapter, unless your synth has Bluetooth MIDI in.
The re.corder connects only through MIDI over BLE which is a wireless MIDI standard and allows for full wireless MIDI compatibility.
Your Synth probably does not read BLE MIDI in but it is likely that your laptop or smartphone will.
Both modern versions of Windows and OSX support it and IOS does as well. Latest versions of Android does connect reliably with BLE midi controllers. More info to come.
Learn more about this topic by reading the following post on our FB Group
“How to connect your re.corder directly to MIDI instruments (without a computer or smartphone)” https://www.facebook.com/groups/re.corderplayersunite/learning_content?filter=140443004736938&post=1051832435585394