Audio

Recording,

Editing and

Playback

DAT

D ATs (digital audio tapes) are capable of audio quality that exceeds what's possible with CDs.

The 2-inch by 2-7/8 inch (5 X 7.6 cm) DAT cassette contains audio tape 3.81mm wide. The cassette (shown below) is about two-thirds the size of a standard analog audiocassette. The two-hour capacity of a DAT cassette is 66 percent greater than a standard 80-minute CD. RDAT

RDAT (recordable digital audio tape) is designed for professional applications, as are the very high quality ADAT machines (types I and 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. DAT time code is similar to the SMPTE time code that we'll discuss in the sections on videotape editing.

Computer Hard Drives

Today, computer hard drives are the choice for broadcast music, commercials, and general audio tracks. Recording audio material on computer hard drives (generally with MPEG-2 or MPET-4 compression, see below) 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, you have almost 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 accidentally misfiled after use. (If you've ever put a CD back in the wrong case, you know the problems this can represent.) And, finally, the hard drive space can easily be erased and re-used.

Data Compression

Both digital audio and video are routinely compressed by 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 using various 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 mechanism.

Unless anti-virus measures are instituted, 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.

IC and PC Card Recorders

PC card recorder Some audio production is now being done with PC card and IC recorders. Both use solid-state memory cards, such as CompactFlash and ATA Cards.

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

The date 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 uncompressed digital format. The latter is used with CD players, DAT recorders, and on computer editing programs that use wave (.wav) files. solid-state recorder

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 stored audio must be played back from the unit, itself. For this reason these recorders have found limited acceptance in production work.

Audio Editing Systems

Audio editing used to require physically cutting and splicing audio tape — an arduous process.

Today, there are numerous audio editing system 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 it quits working and you need to pay for it. Payment is generally between 5 and 50 dollars.

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 will be 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 position.

Much as a cursor is used to mark words in a word processing program to make changes as needed, 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.