Technicolor DTMF sequences

Many SP-mode videotapes duplicated at Technicolor in Livonia and the East Coast beginning in 1989 and ending in 2006 included a sequence of DTMF tones at the start and/or end of the tape. It is not yet known exactly what each tone in the sequence indicates, except there's usually a pause between the first and second tones, the second tone is always 1, the third tone is always #, and the fourth tone is always D. This sequence was used to encode audio and video on the master tape by providing information on settings such as format, running time, audio level balance, volume control, etc. to automatic videotape duplication machines, allowing better replication. On most tapes, the tones are heard on the left channel of the hi-fi audio track. However, on some tapes, the tones are heard either on the right channel of the hi-fi track or exclusively on the linear audio track.