audio recording part i

8/8/2019 Audio Recording Part I

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Audio Recording,

Editing and Playback

A Quick Look Back:

Turntables and Reel-to-Reel Tape Machines

Records and reel-to-reel tape machines used to be the primary source of prerecordedmaterial in TV production. Part of a reel-to-reel machine is shown on the right.

Today, they have almost all been replaced by CDs (compact discs), DAT (digital audiotape)

machines, and computer-type hard drives.

"Vinyl," a term that refers mostly to LP (long playing) records, was the primary medium for

commercially recorded music for several decades. (Note photo below.)

Most vinyl records were either 45 or 33 1/3 rpm (revolutions per minute) and had music recorded

on both sides. Records had a number of disadvantages primarily the tendency to get

scratched and worn, which quickly led to surface noise.

Unlike vinyl records, some of the newer media can be electronically cued, synchronized, andinstantly started things that are important in precise audio work.

Reel-to-reel analog 1/4-inch tape machines, which were relied upon for several decades in audioproduction, have also almost all been replaced first by cart machines (below) and thenby DAT machines and computer hard drives.


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The Return of Vinyl?

Although digital equipment has a multitude of advantages, especially in TV production, in

recent years some audiophile purists have been returning to analog recordings -- especially vinyl

LP recordings. (Note photo above.)

They say that analog equipment, including tube-based amplifiers, renders a fuller, richer tone tomusic. Unfortunately, this latest generation of analog equipment tends to cost many times what it

originally did. Then again, the people for whom such fine nuances of difference are that

important can probably afford it.

Cart Machines

Cart machines (cartridge machines), which are still used in a few facilities, inco Unlike an

audio cassette that you have to rewind, in a cart the tape is in a continuous loop. This means thatyou don't have to rewind it, you simply wait until the beginning point recycles again. At that

point the tape stops and is cued up to the beginning.

Most carts record and playback 30- and 60-second segments (primarily used for commercials

and public service announcements) or about three minutes (for musical selections).

Audio carts are now well on their way to Museums of Broadcasting along with other exhibits

of broadcast technology used in earlier years. Today, audio is primarily recorded and playedback on hard drives, CDs, and DAT recorders.rporate a continuous loop of 1/4-inch (6.4mm)

audiotape within a plastic cartridge.

Compact Discs

Because of their superior audio quality, ease of control, and small size, CDs (compact discs)have been the a preferred medium for prerecorded music and sound


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effects. (However, today, radio stations typically transfer CD selections to a computer disk for

repeated use.)

Although the overall diameter of a typical audio CD is

only about five inches (12.7 centimeters) across, a CDis able to hold more information than both sides of a

12-inch (30.5cm) LP phonograph record. Plus, thefrequency response (the audio's pitch from high to low)

and dynamic range (the audio range from loud to soft

that can be reproduced) are significantly better.

Although CDs containing permanently recorded audio

are most common, CDRs (recordable compact discs)are also used in production. These offer all of the

advantages of using CDs, plus the discs can be re-

recorded multiple times.Radio stations that must quickly handle dozens of CDs use Cart/Tray CD players, such as

the one shown on the right.

As we've noted, for repeated use, CD audio tracks are commonly transferred to computer diskswhere they can be better organized and quickly selected and played with a few strokes on a

keyboard. A computer screen displays the titles and artists, and the time remaining for a selection

that's being played.

In mass producing CDs an image of the digital data is "stamped" into the surface of the CD

in a process similar to the way LP records (with their analog signals) are produced.

When a CD is played, a laser beam is used to illuminate the microscopic digital pattern encoded

on the surface. The reflected light, which is modified by the digital pattern, is read by aphotoelectric cell.

The width of the track is 1/60th the size of the groove in an LP record, or 1/50th the size of a

human hair. If "unwound" this track would come out to be about 3.5 miles (5.7 km) long. Ofcourse, DVDs take this technology even further, but that's a story for another module.

In 2004, MP3 CDs appeared that have the capacity of as many as 10 standard CDs.

CD Defects and Problems


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If the surface of the CD is sufficiently warped because of a manufacturing problem or

improper handling or storage, the automatic focusing device in the CD player will not be able to

adjust to the variation. The result can be mistracking and loss of audio information.

Automatic Error Correction

Manufacturing problems and dust and dirt on the CD surface can cause a loss of digital data.professional CD players attempt to compensate for the signal loss in three ways:

error-correction,

error concealment (interpolation)

muting

Error-correcting circuitry within the CD player can detect momentary loses in data (dropouts)

and, based on the existing audio at the moment, supply missing data that's close enough to the

original not to be readily noticed.

If the loss of data is more significant, error-correcting circuitscan instantly generate data that

more or less blends in with the existing audio. If this type oferror concealmenthas to beinvoked repeatedly within a short time span, you may hear a series of clicks or a ripping sound.

Finally, if things get really bad and a large block of data is missing or corrupted, the CD playerwill simply mute (silence) the audio until good data again appears a solution that's clearly

obvious to listeners.

Audio Recording, Editing and Playback


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DAT

DATs (digital audiotapes) are capable ofaudio quality that exceeds what's possible with

CDs.

The 2-inch by 2-7/8 inch (5 X 7.6 cm) DAT

cassette contains audiotape 3.81mm wide. Thecassette (shown below) is about two-thirds the

size of a standard analog audiocassette. The

two-hour capacity of a DAT cassette is 66percent greater than a standard 80-minute CD.

RDAT (recordable digital audiotape) is

designed for professional applications, as are

the very high quality ADAT machines (types Iand II).

DAT systems use a headwheel that spins at 2,000 rpm (revolutions per minute), similar to what's

found in a videocassette recorder.

Various types of data can be recorded with the audio. Examples are time code and the MIDI

machine control data used in sophisticated postproduction audio work.

DAT Time Code

The DAT time code system, referred to as the IEC Sub-code Format, also insures that tapes

recorded on one DAT machine can be played back without problems on any other machine. DATtime code is similar to the SMPTE time code that we'll discuss in the sections on videotape

editing.


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Computer Hard Drives

Today, radio stations and professional production facilities rely primarily on computer hard

drives for recording and playing back music, commercials, sound effects, and general audiotracks. Recording audio material on computer hard drives has several advantages.

First, the material can be indexed in an electronic "table of contents" display that makes it easy to

find what you need. This index can also list all of the relevant data about the "cuts" (selections) --

durations, artists, etc. Second, by scrolling up or down the index you have (with the help of amouse or keyboard) instant access to the selections.

Once recorded on a hard drive, there is no wear and tear on the recording medium as the audio

tracks are repeatedly played. Another advantage is that the selections can't be accidentallymisfiled after use. (If you've ever put a CD back in the wrong case, you know the problems this

can represent.) And, finally, unlike most CDs, hard drive space can easily be erased and re-used.

Data Compression

Both digital audio and video are routinely compressedby extracting

data from the original signal that will not be missed by most listeners

or viewers.

This makes it possible to record the data in much less space, and, thus,

faster and more economically.

As we will see in the chapters on video where this process is discussed

in more detail, data can be compressed to various degrees usingdifferent compression schemes.

Although hard drives are extremely reliable today, they do occasionally "crash," especially

after thousands of hours of use or a major jolt ends up damaging the delicate drive and head

mechanism.

Unless anti-virus measures are instituted, and assuming the computer is connected to the

Internet or "the outside world," the computer operating system can also be infected with viruses,which can result in a complete loss of recorded material. With these things in mind, critical files

and information should always be "backed up" on other recording media.

C and PC Card Recorders
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Some audio production is now being done with PC card and IC recorders. These and similar

audio and video recorders use a variety of solid-state devices, referred to as flash memory.

These memory cards contain no moving parts and are impervious to shock and temperature

changes.

The data in these memory modules can be transferred directly to a computer for editing.

These units typically give you the choice of two basic

recording formats: MPEG-2, a compressed data format, and

PCM (pulse code modulation) which is an uncompresseddigital format. The latter is used with CD players, DAT

recorders, and on computer editing programs that use wave

( .wav) files.

RAM Audio Recorders

As shown on the right, this new generation of recorders can

be a fraction of the size of other types of recorders.

However, unlike recorders with removable media, the storedaudio must generally be played back from the unit, itself.


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The iPod Era

When iPod-type devices and computers that could "rip" (copy) musical selections from CDs

and Internet sources arrived on the scene, consumer audio recording and playback changed in amajor way.

Users can assemble hours of their favorite music (up to 2,000 songs) on a computer and transfer

it to a pocket-sized, solid-state listening device such as an iPod (on the left) or to one of the newgeneration cell phones (on the right).

"Podcasts" of broadcasts from TV networks

(photo on the left) can also be downloaded andlistened to or viewed at the user's

convenience.

With the iPod nano you can watch up to 5

hours of TV shows, music videos, movies, andpodcasts.

Although Apple Computer initially popularized

these devices, many manufacturers now

produce their own versions.

Audio Editing Systems

Audio editing used to require physically cutting and splicing audiotape an arduous

process.


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Today, there are numerous computer-based audio editing programs available. Many are

shareware that can be downloaded from the Internet.

Shareware can be downloaded and tested, generally for about a month, before the programquits working and you need to pay for it.

Once you pay, you may be given an unlock code that will enable you to use the program for an

unlimited time.

Often, minor updates to the program are free; major updates will probably involve an update

charge.

In addition to basic editing, audio editing programs offer audio filtering, manipulation, and an

endless range of special audio effects.

The audio line above shows how a single channel of sound appears in an audio editor. The

vertical red line indicates the cursor (selector) position.

Much as a cursor is used to mark words in a word processing program to make changes asneeded, the cursor in an audio time line provides a point of reference for making audio changes.

The display above shows how the time lines are integrated into a typical audio editor. Most

programs use a computer mouse to drag-and-drop segments and special effects onto a time-line(the longitudinal graphical representation of the audio along a time continuum).

Audio editing in television production is typically handled along with the video on a video

editing system. This will be covered in more detail in Module 56.

The hard drives on computer-based audio editing systems can also store a wide range of sound

effects that can be pulled down to a time line to accompany narration and music.
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Wrapping Up Audio

Audio Level

Control Devices

Although manually maintaining audio levels is generally the best approach, there are someautomatic devices that can help, and even do some things that you can't do manually.

AGC Circuits

We'll start with a simple audio control circuit, one that is built into most consumer audio

equipment.

If the average audio level is low, an AGC (automatic gain control) circuit will raise it; if the

average level is too high, the circuit will bring it down.

Even though AGC circuits can free you from having to worry about manually controlling audio

levels, they can't intelligently respond to different audio needs.

When no other sound is present, as, for example, during a pause in dialogue, an AGC circuit willin an attempt to bring an audio level up to a standard setting. This can momentarily makeannoying background sounds louder.

If subsequent audio processing circuits (in editing equipment, for example) have AGC circuits,

the problem can get progressively worse as each piece of equipment further increases

background noise.


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AGC circuits can also introduce a reverse problem. Since they respond to loud noises by

quickly pulling down audio levels, this means that words can be lost when an AGC circuit reacts

to a loud sound, such as someone bumping the microphone.

In professional camcorders audio levels can be manually controlled, but in many consumer

(nonprofessional) camcorders the AGC circuit can't be switched off.

Because of the effect of the AGC circuit in bringing up sound levels during a period of silence,

the first few seconds of audio may be distorted until the AGC sets the proper level.

To get around this problem, many videographers (stuck with an AGC circuit they can't switch tomanual control) have the on-camera talent say a few words just before the actual start of the

segment. This can be simply counting, "5, 4, 3, 2, 1," to allow the AGC to adjust proper audio

level. This countdown is then deleted during editing.

Compressors

Audio compressors also bring up low amplitude sounds and pull down the amplitude of loud

sounds -- but they are much more sophisticated than AGC circuits.

Unlike AGC circuits, compressors can be adjusted so that many of the negative effects of

automatic control go unnoticed. Program audio that has been compressed seems louder to the earthan non-compressed audio, a feature that hasn't escaped the attention of the producers of TV

commercials.

Compressors typically have three controls:

threshold, which establishes the audio level were compression begins

compression ratio, which determines the amount of compression (which would be like

expanding or narrowing the area on the right side of the illustration above)

gain, which is simply the maximum output level

Some compressors have only two controls: inputand output levels.

By raising the input level while keeping

the output the same, a greater compression

is achieved, at least until major distortionbecomes evident. The compressor shown

here has VU meters for input and output

levels.


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Compressors and AGC circuits can create problems with music. Although AM rock radio

stations of the 1960s and 1970s may have preferred a maximum-loud sound, the artists often

complained that their carefully balanced audio levels were destroyed. Everything in therecording, whether intended to be loud or soft, came out sounding about the same.

Limiters, Peak Limiters

A basic audio limiterisn't as sophisticated as a

compressor or even an AGC circuit. As the name suggests,limiters simply keep the audio from exceeding a set

maximum level.

By setting a limiter at 0dB, for example, you can be assured

that a sudden loud noise, such as a door slamming, will not "pin" the VU meter and cause majoraudio distortion (and possibly jar listeners out of their seats!).

Audio Expanders

Although they have more limited use, audio expanders

increase the dynamic (loudness) range of audio that has been

overly processed. Audio that has gone through satellite relays, forexample, often ends up being overly compressed.

Expanders can restore the audio to its normal range and in the

process, reduce noticeable background noise.

Audio Filters

An audio filtercan be used to cut or attenuate audio frequencies either above or below

certain points or within the audio range.

For example, you may need to reduce or eliminate the low rumble of air conditioning or the hum

of alternating current. In both cases a filter that eliminates frequencies below about 120Hz maysolve the problem.

On the other end of the frequency range, you may want to try to eliminate upper range

frequencies associated with the rustle of clothes or paper. For this you can try cutting off

everything above about 8,000Hz.

By cutting all frequencies below about 2,000Hz, you can simulate the sound of a telephone

conversation -- or possibly a radio or TV in the background of a dramatic scene. You can use a


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graphic equalizer to do this, or on some audio boards, you can switch a specific filter into an

audio channel.

Production Communication Systems

PL Systems

Since a live, multi-camera TV production involves the closely coordinated efforts ofnumerous people, reliable behind-the-scenes communication links are critical.

Using a PL (private line orproduction line) headset such as the ones shown here, production

personnel can talk to each other and receive instructions from a director.

Most PL orintercom systems are wired together on a kind of party line. In this way, eachmember can hear and talk to everyone else.

Normally, the headset microphones are always on so that both hands can be kept free to operate

equipment.

But, for high-noise situations some PL headsets have a push-to-talkfeature, which means thateveryone's headset mic isn't on at the same time and contributing to the overall noise level.

Another feature that's useful in high noise situations is a large padded earphone, which will help

screen out competing sound.

IFB Systems

In ENG (electronic newsgathering) and EFP (electronic field production) it may be

necessary for a director to relay messages directly to on-air talent while they are on the air. Thiscan be done if the talent uses a small earphone, or earpiece. This system is referred to as IFB


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(variously called interrupted feedbackorinterruptible feedback, or more accurately, interruptedfoldback, because, technically, the signal comes from a foldback bus of the audio console).

When switched to program audio (or the basic audio being recorded or transmitted during theproduction) IFB systems allow on-air talent to hear questions or comments from studio anchors.

Video Recording Media

Although the concept of "live" may have exciting connotations, recording a production has many

advantages.

the length of a program or segment can be shortened or lengthened during editing

mistakes on the part of the talent or crew can be corrected, either by restarting the show,or to some degree during postproduction

program segments can be reorganized and rearranged for optimum pacing and dramatic

effect

program content can be embellished through the use of a wide array of special effect and

editing techniques

production costs can be saved by scheduling production talent, crew, and production

facilities for optimum efficiency, and

once recorded, programs can be time-shiftedor played back to meet the needs of time

zones and the programming preferences of local stations

With the exception of some prime-time dramatic productions that are still done on film, most of

today's television programming is recorded on videotape or computer hard disks. Even whenproductions are produced on film, they are routinely converted to a video recording before


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broadcast.

The Videotape Recording Process

Although videotape is being replaced by various configurations of solid-state memory, it'sstill widely used and, generally speaking, it still represents the highest quality recording and

playback medium.

Videotape resembles audiotape in its makeup. It consists of a strip of plastic backing coated witha permanent layer of microscopic metal particles embedded in a resin base. These particles are

capable of holding a magnetic charge.

The videotape recording process was first demonstrated in 1953, and the first machines went

into service in 1956.

Video recording revolutionized TV production.

Two-inch wide videotape (pictured at the left) was the first practical

video recording medium and one that was used for several decades.

Because it used four video heads to scan a complete

video picture on two-inch wide tape, this system was referred to as the 2-inchquad system.

At the other end of the size spectrum is this Hi8 camcorder (right) that uses

videotape that's only 8mm wide.

All videotape formats use video heads that travel across the surface of the tapeand leave magnetic traces in the tape's coating.

To be able to record the very high frequencies associated with video, not only

must the tape be moving, but also the heads, themselves, must spin over the surface of the

tape. This ends up being a little like walking along a moving sidewalk; the two speeds are addedtogether.

A top view of a headwheel with six record and playback heads is

shown at the left. In a VCR this spins at a high rate of speed while

the videotape (wrapped around the side) moves across the spinning

surface.

This whole scanning process is reversed when videotape is played

back.

The magnetic imprints left in the surface of the tape inducemagnetic changes in the video heads, which are then converted into minute voltages. These are

amplified millions of times before being passed on to various pieces of video equipment

audio recording part i

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