Alesis ALESIS M20 Recording a Time Code Track, 17.3A Recording Smpte from ABS Time, 17-3

Chapter 17, Time Code Tutorial

17.3RECORDING A TIME CODE TRACK

The most stable and trouble-free method of synchronization for any SMPTE time code system is to pre-stripe all tapes with generator-locked time code first, then perform any transfers, recordings, and edits. If all time codes equal the same number, with no offsets, and are the same SMPTE rate and type (drop or non-drop), and tapes are striped completely from head to tail, this is the easiest and most foolproof system.

Make sure you record time code using the sample rate intended for the project! In a digital audio recorder like the M20, there is a direct relationship between the speed of time code and the sample rate. Time code recorded at 48 kHz will play back slow if the word clock rate coming in is 44.1 kHz when the tape is synchronized, making it impossible to lock properly.

17.3A RECORDING SMPTE FROM ABS TIME

As explained in section 17.1, you can always generate SMPTE referenced to the ADAT’s internal ABS time, even if there is no time code on the TC track. However, if you send that tape out of your facility, they must set their INT GEN ABS Offset settings to the same as yours before synchronizing. By recording the ABS Time with offset onto the TC track, they merely have to set their Chase Reference to Tape TC, and the time code will be the same as you used.

A benefit of having the TC track related directly to the ABS track is that all locate points will be numerically related, causing a minimum of confusion. In addition, if the project requires a different type or rate of time code for some reason later, it can easily be regenerated using the INT GEN feature.

1Press EDIT, then INT GEN until the display reads “1 GEN MODE: Play/Rec”.

2Press INT GEN again. The display will read “2 TC START REF:...” Press the UP/YES or DOWN/NO keys until it says “ABS Time”.

3Press INT GEN again. The display reads “3 ABS: XX:XX:XX:XX” where X stands for the last number entered in this page. Using the keypad, enter the number you want to correspond to zero ABS time. Optionally, you may press INT GEN again and enter the User Bits following the procedure in section 11.7d. (Often, this is set to the month, day and year the tape is being made.)

Tip: In most typical video applications, programs start on the hour, with a two minute preroll at the head of the tape. Set the ABS Offset to 00:58:00:00 in most cases. This will make “1 o’clock” equal ABS time 00h 02m 00s 00f 00sf (two minutes from the zero point). Often each reel of a program will have a different hour marker; the “two minutes before the hour” convention usually still applies.

4Leave EDIT mode, turn on INT GEN, and arm the TC track.

5Set the M20’s Clock Source to “INT”. Set the Sample Rate to either 44.1K or 48K. 44.1K is used to conserve space on hard disk systems and if the project will be mixed digitally to compact disc without sample rate conversion. 48K is the better choice if the project will be mixed on an analog desk.

ALESIS M20 REFERENCE MANUAL 1.06 17-3