Like hum, SMPTE time code recorded on magnetic audio tape allows for frame accurate film or video synchronization during the post-production editing process. Being a rectangular wave signal, it is heard as a pulse similar to that of a fax machine or dial-up modem. It has been described as an “obtrusive noise and often a fairly high level signal.”1
Can it be fixed?
In the example on this page, the 1/4” open reel tape was transferred with a two-track head to produce a quick access copy. Since the actual program was on the left channel and the pulse was only heard on the right channel, mono derivatives with just the program proved adequate. Even though the actual process of synching audio to moving image may not factor into the preservation transfer, that does not remove the need for proper playback. Capturing everything on the tape accurately requires an appropriate playback head with time code. However, even with the appropriate head, there is still a potential for crosstalk depending on the recording level of the pulse.
Listen to a tape with SMPTE time code on SoundCloud