Audio: What Every Music Educator Should Know About

by Don Muro

Digital audio has been an important part of the professional recording industry for the past several years. Evolving technologies have now made it possible for many people to enjoy the benefits of this exciting and powerful medium. In this article I will cover the following topics: 1) a review of analog recording, 2) the basics of digital recording, 3) the advantage of digital recording over analog recording, and 4) types of digital audio recording systems.

A REVIEW OF ANALOG RECORDING
The word “analog” can be defined as “similar to” (as in analogy or analogous). In the analog recording process, the sound waves produced by instruments or voices are captured by a microphone which converts acoustical energy (soundwaves) into electrical energy (voltage). As the soundwaves produce changes in air pressure, the microphone produces analogous (or similar) changes in electrical energy. Here are the basic steps in creating an analog musical recording:

1) Instruments or voices move molecules in the air backward and forward. This molecular push and pull movement creates acoustical energy called soundwaves.

2) The soundwaves are captured by a microphone which functions as a transducer - a device capable of converting one form of energy to another form of energy. Microphones convert acoustical energy (soundwaves) into electrical energy (voltage).

3) The electrical signal from the microphone passes through another type of transducer - the record head on a tape recorder. The record head converts the electrical signal from the microphone into an electromagnetic waveform.

4) The tape recorder stores the information on tape.

5) During playback, the tape passes over the playback head. The playback head functions as another type of transducer which converts the electromagnetic waveform into electrical energy (voltage).

6) The voltage from the playback head is processed through an amplifier and then through another type of transducer. In this instance, the transducer is a speaker; it converts electrical energy (voltage) into acoustical energy (sound waves).

7) The sound waves, produced by the backward and forward motion of the speaker, recreate the sound of the original performance.

THE BASICS OF DIGITAL RECORDING

Here are the basic steps in creating a digital recording:

1) Instruments or voices move molecules in the air backward and forward. This molecular push and pull movement creates acoustical energy called soundwaves.

2) The soundwaves are captured by a microphone which functions as a transducer - a device capable of converting one form of energy to another form of energy. Microphones convert acoustical energy (soundwaves) into electrical energy (voltage).

3) The voltages from the microphone are fed into an analog-to-digital (A/D) converter - another type of transducer which converts voltage into digital data. The A/D converter converts the (analog) voltage into digital data that can be recognized and processed by the computer.

4) The digital data is stored until needed for playback or editing.

5) During playback the recording process is reversed. The digital data is sent to a digital-to-analog (D/A) converter - a transducer which converts the digital data back into analog signals (voltages).

6) The voltage from the D/A converter is processed through an amplifier and then through another type of transducer. In this instance, the transducer is a speaker; it converts electrical energy (voltage) into acoustical energy (sound waves).

7) The sound waves, produced by the backward and forward motion of the speaker, recreate the sound of the original performance.

ADVANTAGES OF DIGITAL RECORDING OVER ANALOG RECORDING

Digital recording offers the following advantages over analog recording.

1) Sound quality
Most digital recording devices record at a 16 bit resolution. The higher the resolution, the better the signal to noise ratio of the recording. A 16 bit resolution provides a signal to noise ratio of more than 90 dB. This is far better than the signal-to-noise ratio of most tape recorders. In addition, digital recordings are free of tape problems such as tape hiss, modulation noise, print-through, noise reduction pumping, and wow/flutter.

2) Editing
Tape recorders make it necessary to rewind and to fast forward in order to find specific parts of a song. Most digital recorders use random access which allows you to cue to any location in a song instantaneously. This feature is a tremendous time saver in rehearsals and in the classroom.

Digital recorders also allow you to edit your music with greater accuracy and ease than ever. Most digital recorders allow you to perform non-destructive editing. For example, you can slice or re-arrange your song without actually modifying the original data. This feature makes it possible for the average musician to create complex arrangements which might be impossible to do with tape recorders. (You can recall the original audio data at any time.)

Time compression/expansion is another editing technique available on most digital recorders. A song’s tempo can be increased or decreased without affecting pitch. You can also use a feature called Pitch Shift to transpose a song to a different key without changing the tempo. These two features make it possible to adjust the tempo and/or key to suit any musical requirement.

3) Digital Signal Processing (DSP)
This is an area where digital technology shines. Digital signal processors can add ambience effects (such as reverberation and echo), equalization (tone controls), and other special effects to enhance the original recorded sound.

Some software programs are capable of producing gender-bending effects by making a recording of a female voice sound amazingly like a male voice, or vice-versa.

TYPES OF DIGITAL RECORDING SYSTEMS
Digital recording systems can be classified by the medium used to store data - tape, hard disk, or optical.

1) Digital Tape Recorders
The most common digital tape recorder format is known as DAT (Digital Audio Tape). DAT recorders record a data onto a small cassette (approximately 7” x 5”). These recorders are often used to create stereo recordings of performing ensembles. Portable battery-operated models make it easy to record a group anywhere. For approximately $1000.00 you can purchase a portable DAT recorder and a stereo mic which can produce high quality stereo recordings.

If you want to be able to create multi-track arrangements by recording individual parts one at a time, you should consider a multi-track digital tape recorder. The two most popular multi-track recording formats are the Alesis ADAT format and the Tascam TDIF-1 (Tascam Digital Audio Interface) format. The ADAT format first appeared in 1992. It records eight tracks of digital audio onto an S-VHS videotape. The TASCAM format also records eight tracks, but records onto a Hi-8 tape. Both formats allow multiple machines to be synchronized to increase the number of tracks available.

2) Hard Disk Recorders
Hard Disk recording systems can be classified as Modular Hard-Disk Recorders or as Digital Audio Workstations.

A modular hard disk recorder can be thought of as a computer designed with only one function - to record digital audio. It is a self-contained unit with a built-in hard disk and mixer. Some units also include effects processors which can add ambient effects such as echo and reverberation to a recording. Modular hard-disk recorders are very portable and use cassette deck-type controls for recording and playback. Examples of these type of recorders include the Roland VS-880 and the Korg D8.

Digital audio workstations typically require the following components: 1) a PC or Macintosh computer, 2) a software package, and 3) a hardware interface to get audio into and out of the computer. Although computers are sold with built-in sound cards, the recording quality of many cards is not good enough for high quality recording. Several manufacturers offer high quality sound cards with 1) a variety of input types (analog/digital) and 2) a variety of inputs and outputs (from two inputs to as many as needed). Digital audio workstations offer tremendous flexibility in editing digital audio. The large display area of a computer monitor is a great aid in visual sound editing. In addition to stand-alone recording software, companies such as Cakewalk, Steinberg, Opcode and Mark of the Unicorn offer MIDI sequencing programs with digital audio recording capability. These programs enable you to record any combination of MIDI tracks and audio tracks.

3) Optical Digital Recorders
Optical recording formats include MiniDisc, CD-R and DVD-R.

MiniDisc recorders are portable units which use a 2.5 inch optical disc for storing digital audio. These recorders use Sony’s ATRAC (Adaptive Transform Acoustic Coding) data compression in order to maximize the storage capacity of the disc. However, many audio professionals agree that there is a discernible difference in sound quality between the Mini-disc format and CD format. The Yamaha MD8 is an example of a MiniDisc recorder with 8 tracks.

Unlike the other formats described in this article, the CD-R format is not used to record live audio. Instead, it is used to create compact discs. Although stand-alone CD recorders are available, most CD recording is done on a computer. CD mastering programs such as Steinberg’s WaveLab and Sonic Foundry’s CD Architect are powerful tools which combine high-level audio-editing capabilities with CD recording functions. With these programs, you can do the following: 1) import digital audio from a modular hard disk recorder or from any digital or analog source into the computer, 2) adjust the volume levels of different songs, 3) add fade-outs, 4) arrange the song order, and 5) “burn” a CD which can be played on a standard CD player.

DVD-R (Recordable Digital Video Disc) technology is still in the process of being standardized, but you should be aware that this technology is on the horizon. There are presently several DVD formats vying for acceptance - DVD-RAM, DVD+RW, DVD-Audio, etc. When the dust eventually settles, we will have a level of audio fidelity that has only recently become available to high-end recording studios.

As you can see, there are many choices when entering the world of digital audio. You should first decide on what you want to accomplish musically - make digital recordings of your performance groups, create multi-track recordings, copy and edit old analog tape recordings, etc. When you have decided on your applications, it will be easier for you to select the appropriate hardware and software. Remember that technology is constantly changing - keep abreast of these changes by reading periodicals and by talking with someone who is active in the field.

Don Muro is active as a composer, performer, author and educator in the field of electronic music. His most recent publication is Sequencing Basics (Warner Bros.). He can be reached through his website at donmuro.com.