TIPS FOR MIXING TO DAT

If your preferred mixing medium is DAT tape, here are
some important details that will assure the easiest mastering
session and therefore the best sound quality for
your finished product.

 

 

"POLISH" YOUR BLANK DAT

"Polishing" simply means to fast-forward & rewind a new blank tape before recording on it. This will most often strip off any microscopic particles on the tape surface that can cause glitches. This is a recommended practice for any format of analog or digital tape, either audio or video.

RECORD AT 44.1KHZ

The sampling frequency of an audio CD is 44.1Khz. If your DAT is recorded at 48Khz, then a sample rate conversion has to be performed in order to get the proper sampling frequency. Although there are many good sample rate converters (such as the HHB BitBox or Sonic Solutions SR Conversion used by D.E.S.), none are totally transparent, and you will lose some sonic detail by having to use this process.

Don't be fooled into thinking that recording at 48khz will give you a better high frequency response. In theory this may appear to be true, but in reality the digital filters in the D-to-A converter have a sharp cutoff at 20khz, so the extra response is not realized in playback. Even so, any extra high frequency brilliance gained by the higher sampling rate would be negated by the sample rate conversion process.

There are now 24 bit DAT machines, such as the Tascam DA-45HR at D.E.S. If you have this capability, by all means use it. However, most mastering houses will not invest in a DA-45HR or other 24 bit DAT machines unless they become widely used, so be prepared to have to take your machine to the mastering house, or to pay for the rental of one.

Also, you must be sure that your mastering house has full 24 bit capability in order to realize the advantage of your 24 bit recording. Even if you mix to standard 16 bit DAT or Audio CD-R, there is a HUGE advantage to mastering at 24 bit or higher resolution. Don’t be fooled by systems that claim 24 or 32 bit "internal processing". Most of these workstations cannot truly record or output a proper 24 bit digital signal; this is just a spec-sheet manipulation to fool customers into thinking it is something it is not. Most workstations will pass 18 bit at best.

Caveat: We are moving into the brave new world of high-density audio. The first high-density mastering system is represented in Digital Editing Services' Sonic Solutions SSHD, which will up-sample the incoming digital audio to 88.2khz (if recorded at 44.1k) or 96khz (if recorded at 48k), and will then down-sample to 44.1khz when burning the CD master disc, DDP or DAT. We have not formulated an opinion yet as to whether 48khz sample rate on the DAT would offer any advantage in this case, but it is doubtful. However, as we move into the new DVD-Audio and SACD formats, which will be 96khz/24 bit, it may be the case that 48khz is better for up-sampling to 96k than starting from 44.1khz. Check back here for details.

 

 

RECORD YOUR DAT WITH A-TIME

A-Time (absolute time) is a time code that is recorded on the control track of the DAT, and is read out in hours, minutes, and seconds on the DAT's display. In order to get proper A-Time on your DAT, two things have to happen:

1. You must begin recording from the very beginning of the DAT tape. Rewind to the beginning of the tape, put the machine in record, and record silence up to the beginning of the first mix on the DAT. This begins the A-Time process and you will see the machine’s counter count up from 0:00. Whether the DAT is recording silence or music, it is recording the control track. Begin the first song after approx. 1 minute (see next subject).

2. The control track has to be continuous. If there is a break in the control track, you will lose A-Time. A break in the control track happens whenever there is unrecorded tape, no matter how little, between tracks. Even a fraction of a second of unrecorded tape will cause this.

This most often happens when you stop recording on a blank DAT, and then begin recording again from the same spot - the machine will sometimes leave a little gap between the last recording and the new one. This is why you may suddenly lose A-Time half way through a DAT. There is a simple way to prevent this; always let the DAT machine record several seconds longer than necessary after you finish a song, then when you are ready to mix the next song, back-cue the DAT a couple of seconds, so you go into record/pause where silence has already been recorded, and therefore there is a control track.

Tip : If your DAT machine has a switch marked “Program Time”, turn this off. This was a hi-fi feature that starts the time counter over at 0:00 at the beginning of each song, and defeats A-Time recording.

 

 

 

BEGIN RECORDING THE FIRST MIX AT APPROXIMATELY ONE MINUTE ON THE DAT TAPE

If there is going to be a problem with a DAT tape, most often it will occur during the first thirty seconds of tape, where problems may have occurred during manufacturing in spooling or loading. Also, I have personally had to repair DATs that have come loose from the spool, and in a case like this you can count on loosing the first 10 seconds or so. Giving yourself one minute of space gets you well into the “good” tape. Also, it gives the mastering engineer plenty of room to pre-roll to make sure all clocks have locked in and stabilized.

As outlined above in the A-'Time discussion, start recording silence from the beginning of the DAT tape so Absolute Time is recorded in the control track. Record silence to 1 minute 10 seconds or so. Back-cue the DAT to 1:00, and go into record/pause for the first track. The exact start time of the first track is not critical - 0:58, 1:03, whatever - as long as you are approximately one minute into the DAT.

THE BIG MISTAKE: I see it all the time; people who start the first song at the very beginning of the DAT. They mistakenly think that this space will directly translate to the CD, and any extra space will show up before the first song begins. The problem here is twofold.

Firstly, as pointed out above, any tape problems or glitches in the DAT tape itself usually occurs within the first few seconds, so the beginning of the song is about 70% more likely to contain glitches than if it were started at 1 minute as recommended.

Secondly, it takes digital converters a couple of seconds to read the control track off of the DAT and lock to the digital clock, and until this happens, DAT machines will mute both the analog and digital outputs. When the first song begins at 1 or 2 seconds on the DAT, the attack of the first note will invariably be chopped off on some DAT machines' playback even though it may play on the machine that recorded it just fine.

 

NEVER SWITCH SAMPLING RATES

Whether your DAT is recorded at 44.1k or 48khz, it should stay at the same frequency all the way through. Some of the most sophisticated digital processing gear that may be found in a mastering room is VERY sensitive to sample rate changes, and in some cases the gear will glitch and have to be powered down, or even will be damaged. Also some processors will pass huge glitches where the sample rate changes potentially damaging monitor speakers.

THE BIG MISTAKE: If you accidentally switch sampling rates part way through your DAT, what will compound the problem is if the next mix begins immediately after the sample rate changes. As I explained before, it takes about a second or more for digital devices to lock & unmute when they receive a new clock signal, and if a mix starts too soon after a clock change, the beginning of the first note will be clipped.

TIP: Even if your DAT doesn't switch sampling rates, the safest thing to do is to let the DAT tape roll in record for a few seconds before you begin the next mix. If you followed our advice on keeping the control track continuous, you also let the tape roll for several seconds after the previous mix ended, and back-cued a couple of seconds before going into record. This means that you will have at least 9 or 10 seconds between each mix. You do not need to be concerned with the amount of time between mixes on your master DAT or disc. The mastering engineer has total control over the song spacing (and order) for the final master. Too much time between mixes is much better than too little.

 

 

MAKE SURE YOUR DATS ARE PROPERLY ID'D

DAT machines will automatically write ID's while recording, but sometimes they will miss one, or write unnecessary ID's because of noise. Go back and check your original master and make sure that every track has an ID and that they are properly numbered. Manually write ID’s where any were missed, erase any erroneous ones, and renumber if necessary.

Tip: These manually-placed ID’s don’t have to be that accurate. The mastering engineer will always back up and begin recording into the editor several seconds before the beginning of a song.

THE BIG MISTAKE: One of the things that I most hate to see, and that happens way too often; a DAT with no A-Time and mis-numbered or unnumbered ID's. Or the worst case possible: no A-Time AND no ID's! This is a mastering engineer's nightmare.

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  Sorry, that's all for now. Check back soon. Last updated 10/3/01.

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