by: Roger Nichols
On an April morning in 1990, I was driving down Hollywood Blvd. by Graumans
Chinese Theater, thinking about my approach to this article, when I looked
up ahead and saw a bush on the side of the road burst into flames. People
were running over to it to see what had happened. As I pulled over and got
out of my car, I heard a voice say "I have some information for you.
Please call me." I just knew that it was time for me to receive the
Ten Commandments of Digital Recording. As it turned out, the bush burst
into flames because of a natural gas leak under the sidewalk, and the voice
was from my pager. I realized that I was going to have to brave it on my
own.
In my opinion digital recording is a great medium for storage of audio information.
You can move recorded instruments from one track to another without any
loss, punch in and out of record in the middle of a vocal line without holes
the size of the Grand Canyon, make exact copies of your tape for safety
reasons or to duplicate sections to edit into other places, perform non-destructive
edits by assembling the pieces to a second machine as you would in video
editing and you can make a record at home that sounds as good as what can
be done in lots of major recording studios.
All of this is well and good, but with every plus, there are equal but opposite
minuses. Knowing what to expect can keep you from any major pitfalls and
then your album can sound as good as the studio bills look like it should
sound.
1. Record in as quiet a place as possible: Professional studios all over
the world are being re-designed to provide a quieter environment for digital
recording. When you record analog the quietest thing on the record will
be the tape hiss. On your new digital recording there will be no tape hiss
to cover up the sound of the air conditioner, the toilet flushing in the
next room or the dog barking next door.
2. Recording levels are important. With digital machines you should record
as hot as possible without any "over" lights coming on. The "over"
light means that you have just clipped your signal. This is an absolute
clip, not a gradual limiting. It will usually sound like a large click or
a tearing sound. Some engineers have said that they were told that a few
red lights once in a while were alright as long as the didn't stay red for
a long time. That is the same thing as saying that it was ok to drive through
the red light because it had only been red for a little while. It is not
a good thing to do, so DON'T DO IT!
3. Equalize the instruments the way that you want them to sound, and then
stop. A keyboard player's gene pool will not allow him to stop changing
things after the sound is perfect, but a recording engineer should be able
to stop. Digital recording will faithfully reproduce what you put on the
tape. When recording analog, you must make up for the deficiencies of the
analog medium by over compensating for the losses. Percussive sounds have
a tendency to deteriorate with time on analog tape. This is not so with
digital tape. What you start with will be what you end up with.
4. Clean the heads and maintain a clean machine. In 1959 I heard a saying,
"Cleanliness is next to high fidelity." Well, nothing is closer
to the truth when dealing with digital recordings. The best thing about
digital recording is that it plays back exactly what you record. The worst
thing about digital recording is that with enough tape errors it will playback
nothing.
Tape errors usually come from dust scratching oxide off of the tape. The
oxide piles up on the heads and causes errors. Digital recording is a very
robust medium. Extra data is stored along with your audio to make sure that
if there are any errors on the tape that they can be corrected and the signal
that comes back out of the machine is exactly what you put in to it. If
the error rate gets too high and the error correction circuitry can't fix
the data, it turns everything off until it gets good data to put out. Analog
tape was more forgiving in this department. If what was left on the analog
tape sounded like crap then the machine would just put out the crap. Personally
I would rather nothing come out than something sub-standard. Oh well.
5. Preformated tapes are common to video editors. Black video information
is put on the tape from one end to the other before any meaningful work
is done on the tapes. This formatting operation puts what is called a control
track on the tape. This control track provides information to the playback
electronics so that the machine can synchronize the electronics in the machine
with the information coming off of the tape.
Much the same thing takes place in digital audio multi-track machines. You
will always be safe if you pre-format all of your tapes before you use them.
It is possible to record on a tape that is not formatted, but you are opening
up a can of worms and you should only do this if you really know what you
are doing. On the Mitsubishi and Otari 32 track digital machines you can
format the tape as you are recording, but if you stop the tape at the end
of one take and then start up again for the next take there will be a seam
in the control track that can never be recorded over. During the Ricki Lee
Jones album, which was recorded on a Mitsubishi X-850, we did not pre-format
the tape because "I knew what I was doing." Everything was fine
until Ricki decided that she wanted to play a part that needed to extend
past the end of the track. The part crossed the seam in the control track
and the X-850 turned it into lunch meat. We had to rent another 32 track,
format the tape, transfer the take we were using and then re-do the ending
that she wanted to add to the song. It took about four hours to undo what
30 minutes of formatting would have prevented.
The Dash format machines have an additional record mode called "Assemble."
This mode will allow you to seamlessly extend the control track during intermittent
recording so that you don't get stuck. You must, however back up a ways
into the previously recorded material and go into record mode before the
seam for this to work. So, know your machine and plan ahead. If you are
recording live performances and recording non-stop through the entire reel,
then everything will be fine. If you will be starting and stopping the tape
during the recordings, use pre-formatted tapes.
6. When dealing with DAT and 2 track machines you do not have to worry about
formatting tapes, but you do have to make sure that you leave plenty of
run-up and run-out on either end of your mixes. Remember that a digital
machine needs the control track signals to synchronize all of the various
electronics and transport mechanisms and that it takes a second or so after
the tape starts before audio starts coming out. If you start the tape machine
recording to close to the beginning of the music, chances are that the front
of the tune will be clipped off during playback. It is better to have 10
seconds too much before the start of the music than a quarter of a second
cut off the beginning of a killer mix.
On an open reel machine, if you need to add some blank tape between tunes
to improve the spacing, you can't use virgin tape to do it. The tape must
contain the control track information or else there will be another mute
at the beginning of the next tune. Use a piece of tape that has control
track recorded on it.
When it comes to DAT machines, some machines are able to start recording
closer to the beginning of the tape than other machines. It is possible
to record something at the top of the tape on a Panasonic 3500 DAT machine,
and then not be able to play back the first few seconds on a Fostex D-20
DAT machine. Leave extra room!
7. Make back-ups of your masters. If you are using a digital multi-track,
make safety copies of the master tapes after the original tracking sessions,
and then every couple of weeks after that. It sounds like a lot of extra
expense and work, but believe me that it is cheaper than re-recording the
stuff that got lost or damaged. During all of the Steely Dan records, we
never made safety copies of any of the multi-track tapes. We knew that it
was risky, but we would never want to use an analog copy of anything we
did because of the generation loss, so we elected not to back up our tapes.
During the Gaucho album a tune got erased. We did not have any copies of
the tune. It cost over $60,000 to try to re-record it. The re-tries didn't
come out as good as the original so it never made it onto the album. With
digital recording there is no excuse for not making copies.
If you are printing mixes to a DAT machine, put in a second tape and print
the mix a second time. If you are using a professional digital two track,
print a second copy of the mix and put on another reel. In March of this
year I recorded and mixed three tunes for Michael Franks. When it came time
to assemble the mixes for mastering, the Mitsubishi X-86HS ate one of the
mixes. I had printed safeties of everything, so all I had to do is replace
the mix with the safety and I was back in business.
8. Listen back to your tapes. It is always a good idea to play back your
mixes after you have printed them to make sure that they made it to the
two track. Everybody usually does this, but very few people I have run into
listen back to digital copies of their tapes after they are made. It has
been pretty much assumed that digital clones are exact copies of the original.
This is true in most cases, but I have run into problems when making copies
of tapes. It may be a temporary problem with one of the machines, or a design
problem in a particular machine, but the only way you are going to find
out is to listen. Compare the original to the copy. Make sure that they
are the same. In certain cases, I have achieved better results making the
copy in the analog domain than in the digital domain. The companies involved
have been put on notice. Hopefully it will get better, but in the meantime,
listen to the copies.
9. Sample rate choices will turn any sane engineer into a blithering idiot.
The four basic sample rates are 48kHz, 44.1 kHz, 44.056kHz and 32kHz. The
easiest one of these to deal with is 32kHz. That is because you won't be
able to find a machine that records it, it is only used, maybe, for broadcast
of digital audio information and it is the worst sounding of any of the
sample rates because it won't allow any frequencies over 15kHz. If you insist
on recording anything at a 32kHz sample rate we will know about it and you
will not get your next issue of EQ magazine, and your subscription to Road
& Track will be forwarded to Montana.
If you can't decide which sample rate to use, go with 48kHz. Everybody else
does their multi-track digital recording at 48kHz, so you might as well
do it to. If you are recording a digital multi-track while it is locked
to video, you may be better off using 44.1 kHz because of the ease of synchronization
between the video and digital machines at this sample rate. There are actually
devices that will let you sync anything to anything no matter what the sample
rate, but that is a whole other article.
If you are mixing to a DAT machine in the studio and you want to be able
to make copies of the DAT tapes at home between two home type units, then
by all means set the studio machine to 48kHz. Home DAT machines will not
make copies of tapes that were recorded at 44.1kHz. Also, the home DAT machines
can not record analog in at 44.1kHz, so if you recorded some stuff in the
studio at 44.1kHz and then want to record something else on the tape at
your home studio, the sample rates will change between cuts and mute the
output of the DAT machine during the transition.
Sony 1610, Sony 1630, JVC DAS-90 and DAS-900 machines can record at 44.1kHz
or 44.056kHz. The 44.1kHz is the standard for CD masters. 44.056kHz is for
locking to a video reference. Sony F-1 and compatible video based machines
record at 44.056kHz if they are NTSC standard units or 44.1kHz if they are
PAL format units.
There are plenty of sample rate convertors around, and they are pretty good
at maintaining the quality of the audio during the conversion. I personally
do all my recording and mixing at 48kHz, and then go through one sample
rate conversion to the CD master, which must be at 44.1kHz whether you like
it or not.
10. When it comes to deciding what format to use, you have to weigh many
variables. The number of tracks, the reliability of the machine, the cost
of the rental or purchase, the ease of use, the availability of another
machine of the same format for copies, which machines are compatible in
case you have to go somewhere else to work on part of the project and one
of the most overlooked considerations, what the cost of the tape is for
the particular machine in question. Try to figure out how many tracks you
need and how many reels of tape you are going to use. Factor this in along
with the cost of the digital multi-track. The machine that you thought would
be the most cost effective for your project may end up being the most expensive.
By the way, an hours worth of 24 track analog tape costs 4 times as much
as an hours worth of 24 track digital tape. During the Steely Dan "Gaucho"
album we used 360 rolls of 2" analog tape.
Digital tape comes in 2 basic groups. Reels of tape for reel to reel machines
and tape loaded into some sort of cassette for hands off ease of handling.
The tape available on reels comes in widths of 1", 1/2" and 1/4",
and is stored on your choice of 10 1/2", 12" or 14" reels.
The length of time that can be recorded on a reel of digital tape depends
on the transport speed of the machine and the size of the reel that you
are using. Cassette based tapes include 3/4" video tape, 1/2"
video tape, DAT tapes, 8mm video tape and proprietary 8mm digital tape.
Table 1 shows the playing time vs. speed & reel size. Table 2 shows
what machines are compatible with what other machines.
11. When making razor blade edits on an open reel digital machine, you must
leave a hair line space between the two pieces of tape that are being edited
together. This tells the machine that there is indeed an edit coming up
and causes the electronics to perform a cross fade across the edit point.
Use a residue free marker to mark your tapes. Under no circumstances use
a grease pencil to mark digital tape. I will personally come over to your
house and do strange things to your dog with a fork. Make sure that you
use "digital" splicing tape. This tape is specially formulated
not to leave any residue behind. I guarantee that if you use regular analog
splicing tape that your edits will not play back two weeks after you did
them.
12. Finally we get to the end product of all of this high tech foolishness.
Remember that all albums end up digital in the end. Whether they are analog
or digitally recorded in the beginning, it all comes out in the wash. Your
master mixes will be transferred somewhere to a Sony 1630 master tape and
then be sent to the CD plant where they make those little silvery disks.
If you are assembling your final mixes onto a digital 2 track machine, you
must obey the following rules before mastering:
Place plastic leader before the first tune and at the end of the last tune
of your album. There must be at least 1 1/2 seconds of blank formatted digital
tape between the leader and the start of the first tune. The spaces between
the tunes must be made up of blank formatted digital tape, not leader. Be
careful when editing in these little spaces, digital tape will only play
in one direction. If the piece is in backwards the digital machine will
mute. After the last tune, use blank formatted tape for a few seconds before
the end leader comes up. After the end leader, place about 1 minute of reference
tone. There is no need for multi-frequency tones but you can put them there
if you want. The one that is needed is 1kHz at 14dB below clipping. If the
level is different than -14dB then note it on the box label.
Well, that about covers it. If this helps get you through any rough spots,
then it was all worth the effort. Have a good time with your digital recording,
I'll be down at Tower Records waiting for your CD.
Table 1. Tape playing time
Reel Size 30ips 45ips 15ips
10 1/2" 4600ft 30 min 23 min 60 min
12" 7200ft 48 min 36 min 96 min
14" 9700ft 64 min 48 min 128 min
Table 2. Compatibity Between Machines. Machines with the same letter will
play each others tapes. I know that with the video formats that it is possible
to use other video decks and tape sizes, but these are the intended formats.
Machine Tape Width Compatibility Group
Sony 24 track 1/2" 30ips A (first 24 tracks only)
Sony 48 track 1/2" 30ips A
Tascam 24 track 1/2" 30ips A
Studer 48 track 1/2" 30ips A
Otari 32 track 1" 30ips B
Mitsubishi 32 track 1" 30ips B
Mitsubishi 16 track 1/2" 30ips C
3M 32 track 1" 45ips D
3M 4 track 1/2" 45ips E
Mitsubishi X-80 1/4" 15ips F
Mitsubishi X-86 1/4" 15ips G
Mitsubishi X-86-C 1/4" 15ips G, F playback
Mitsubishi X-86-HS 1/4" 15ips H,G
Sony 3202 1/4" 15ips J
Sony 3402 1/4" 15ips J
Sony 1610 3/4" Video K
Sony 1630 3/4" Video K
JVC DAS-90 3/4" Video L
JVC DAS-900 3/4" Video L
Sony F-1 1/2" Video M
Sony PCM-701 1/2" Video M
Sony PCM-601 1/2" Video M
Sony PCM-501 1/2" Video M
Nakamichi PCM-100 1/2" Video M
dbX-700 3/4" Video O