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Recording Handbook
Chapter 2: Getting Your Sound On Tape

 2.Getting Your Sound On Tape

IN THE OLD DAYS... "Analog" was the only kind of recording available to the average musician. The first sign of the digital revolution reaching the streets in the late 1980's were DAT recorders, Alesis ADAT 8-tracks, Tascam DA-88 8-tracks and later, hard disc recorders like the Emu Darwin, Akai and Vestax machines came along and the genie was out of the bottle. Of course the early digital samplers were also in the mix. Now you can run a digital multi-track recording session from your iPad, for crying out loud! 

Still, the process is the same even though there are different technical considerations and format specific issues to address.

a. The Analog Recording Process

Analog recording devices use a plastic tape coated with magnetic particles moving across a magnetic recording head at a constant speed to record and playback. There is always an "erase head", first in the tape path, to erase and re-align the tape particles before they hit the "record head". In the "two-head" machine there is one head for both recording and playback. The "three-head" design features one head dedicated to recording, the "sync head", and another for playback, "the repro head". Professional machines have three heads.

There is a limit to the intensity of the signal that the tape particles can actually absorb and reproduce. The two parameters that interact to maximize the tape's ability to correctly record and playback are "tape speed" and "bias". At a faster speed, there is more tape area for a given signal, i.e. more tape particles to record. Most professional analog multitrack recorders run at 30 ips (inches per second). "Bias" is a process that was discovered by accident. It was found that when a high frequency signal, 100 Khz or so, much higher than human hearing, was recorded along with the normal signal, the magnetic particles did a better job of recreating the higher frequencies.

It is a complicated process and there are lots of things to go wrong! The tape machine must be mechanically and electronically aligned to very fine specifications. First, to ensure that it physically handles the tape gently during shuttling, rewind and fast forward. Although tape formulations have improved greatly over the years, mechanical problems can damage the tape by stretching or wrinkling it. There is no error correction for this! Treat your tapes with care and respect. Other problems include loss of particles off the tape, called shedding, speed fluctuations which produce "wow and flutter" and improper tape to head contact.

Furthermore, the electronics have to record the input signal and play it back faithfully. This is where tones on your master tapes becomes so important. They are required to properly align the electronics in the tape machine so when you work at different studios, your tape sounds like you remembered. When all these parameters are aligned correctly, you stand a good chance of hearing back a reasonable facsimile of what you recorded previously.

b. The Digital Recording Process

The digital recording process is far simpler mechanically, but much more involved electronically. The input signal is sampled 1000's of times per second and each acoustic slice is given it's own digital number, consisting of 0's and 1's. Theoretically, the "analog-to-digital converter" (ADC) receives the analog input and converts it into a stream of numbers and conversely, the "digital-to-analog converter" (DAC) reverses the process.

The "sampling rate", or how many times per second the sound is sliced is the main factor in how well the sound will survive its digitization. CD's are sampled at 44.1 K or 44,100 times per second, and that has become an industry standard. Some formats offer 48 K sampling as well. DAC's and ADC's aren't created equally however and there are differences in how these machines sound, despite the theoretical consistency of 0's and 1's!

Digital tape machines use mechanical transports and plastic tape as a storage medium for the digital information. The Alesis ADAT and Tascam DA-88 are examples of the inexpensive digital tape multi-tracks. Another approach gaining acceptance are hard disc recorders. Some have computers with software as front-end controllers, like the Digi-Design and Soundscape machines, while others are dedicated boxes you plug hard discs into for storage, like the EMu Darwin, Vestax and Akai recorders.

With these random access digital recorders, the size of the hard discs limits the amount of recording time. Locating is a snap, as is editing. When this approach is combined with a computer as the interface, you have a powerful word processor for music. Anyone who has used a Mac or Windows on an IBM knows how to drag and click with a mouse and that's basically how you manipulate the sound files.

c. Theory of Multi-track Recording

Multi-track recorders are simply tape machines that allow you to record tracks and then overdub additional tracks in any order. For instance, you might record a drummer on four tracks, then go back and record a guitar part, etc. To do this, the tape machine must be able to record one track while its playing back the others. In an analog machine, it must do this from the same recording head. This is the job of the "sync head".

Digital machines don't rely on sync heads and repro heads, they're just reorganizing 0's and 1's. Depending on the device, sometimes the tape based digital machines are not as flexible as the random access machines.

It is possible to "lock up" more than one multi-track tape machine to get more tracks. This is usually done with two identical machines and SMPTE. SMPTE is an acronym for a timecode that was originally developed for the motion picture industry. It sounds like a high pitched squeel but to devices that can "read" it, it looks like a running clock. For lock up, we would "stripe" two multi-track tapes; for one song we might need five minutes, so we set the SMPTE "writer" to write from 0:00:00:00 to 5:00:00:00 minutes.

SMPTE is displayed as "hours:minutes:seconds:frames:sub frames", although not all devices read subframes (there are 80 subframes). There are four types of SMPTE. They are 30 frame per second (fps) drop frame, 30 fps non-drop frame, 25 fps, and 24 fps. In the United States, audio professionals generally use 30 fps non-drop frame and in England and Europe, they use 25 fps. The 30 fps drop frame, sometimes called "29.97", is used for video and film applications in the United States.

As has become the industry practice, we record this SMPTE on the highest edge track on each tape. For example, track 8 on an 8-track, track 24 on a 24-track, etc.. So, now we have identical "striped" tapes on their respective multi-tracks. The next step is to use a synchronization device designed to read the SMPTE off each machine and control the motors of both to keep them locked together. 

One machine becomes the "Master" and the other, or "Slave", chases the master machine. Two of the most popular professional systems that do this are the Lynx and Adam Smith synchronizers. This is the basic concept and it is possible, with the right interfaces and connections, to lock up different types of multi-tracks, VCR's, timecode equiped DAT machines, digital editors, etc.

The concept is simple, the execution can be complicated. The most important thing to remember is what kind of code you've got. Keep good notes! 

 

     
     
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