LTC is a biphase-mark audio signal. For gear that has to chase the code, use WAV — MP3 is lossy and can corrupt the waveform. Give devices a second of pre-roll; a from-silence start has no leading edge on its first frame. The clip runs start to end inclusive, so the final frame equals your end timecode.
Add/subtract and conversions are drop-frame aware. Frame-rate convert keeps the same wall-clock instant — useful for checking what a cue lands on at 25 vs 24 vs 30.
Route LTC into your computer's line/mic input (or a USB interface) and press Start. This is a diagnostic tool — it tells you what timecode is on the wire, the frame rate, and whether it's clean and locking. It is not a frame-accurate master; use hardware to actually chase. Browser mic processing is bypassed where possible for a cleaner read.