Another import thing I need clearing up: why is the beep so long!!?
I can answer that one, RedForShort. In my former career, I used DIR tapes for staff investigations (not the police but the interviews were always conducted to PACE standards - but I can't say more than that, sorry!)
There are always two DIR tapes, both sealed in their original wrappers. For the purposes of a clean chain of custody, both tapes are unsealed in the presence of the subject of the interview and both new tapes are placed in the recording unit. Because they are similar but not identical to cassette tapes (see next para), there is always a long piece of blank (non-recordable) tape at the beginning and at the end because it is wound around the spools. The long beep indicates that it is the blank piece of tape that is being spooled, which is why no one speaks during the beep. Once the beep stops, it indicates that the DIR tapes are recording.
On conclusion of the interview, one DIR tape is always sealed in an evidence bag then and there in the presence of the subject and the evidence bag signed. It is retained in a safe place unless it is needed to counter allegations of tape-tampering. The other tape is the "working tape" because it is used to produce a typed transcript of the interview. The reason why DIR tapes are not identical to ordinary cassette tapes is because they already carry a pre-recorded time stamp (a voice saying "one minutes and ten seconds, one minute and twenty seconds, one minute and thirty seconds" and so on) so that an exact quote can be pinpointed on the DIR tape. The pre-recorded time stamp can only be heard on a special DIR transcription player.
Phew! Bit technical but HTH!