Understanding Digital Audio

Mark Frankel
Reprinted with permission. From Tempo, The Official Publication of the
New Jersey Music Educators Association. October, 2001, Thomas Mosher, Editor

Your students already know about it. They are probably carrying around little mp3 players and downloading tons of music off of the internet. My students, without my asking for them, burn CD's for me which contain recordings of pieces we are currently working on in band, orchestra and jazz ensemble. It is pretty amazing what our students can do with technology. I asked my brother Mark, an audio engineer and musician who currently works for Sennheiser Electronics Corp., to write this article to give a basic introduction to digital audio and how you can get started using it in your classroom. Take it away, Mark...

LP's; cassette tape recorders; dolby NR. These are the buzzwords of a bygone era. Words and codes like mp3, wav, and CD-R are their successors. The way the world experiences music has always been in a state of flux, but since the advent of digital technology and the PC, things are changing more rapidly than ever. With the massive proliferation of user friendly software, inexpensive equipment and a built-in distribution network known as the internet, it has never been easier to create, record, distribute, and listen to music. Let's take a closer look at the various components needed to get the most out of your computer without spending a fortune.

Not too long ago, everything was analog. Music was (and sometimes still is) recorded magnetically by tracing sound waves and playing them back in a similar fashion. Then in the early eighties, the compact disc was introduced and it revolutionized the music industry. Still some don't understand what it means to record and playback digitally. Here's a simple, albeit vague explanation: in essence, digital recording breaks up the audio stream into small consecutive fragments or snapshots called samples, assigning each one a binary number (a number consisting of two numerals, 0 and 1). Each digit is referred to as a bit. According to the Compact Disc standard set by the Audio Engineering Society, the samples are taken 44,100 times per second (measured in Hertz) and each sample is sixteen bits long. Thus the CD specification of 44.1 kHz/l6 bit was set.

How does all this benefit the audio fidelity? By assigning code to the audio stream, it allows the music to be copied time and time again with no loss; the code is simply read, rewritten and played back without any degradation at all. Also, it records and plays back without introducing any noise. With vinyl LP's and cassettes, the recording and play back mediums themselves generated a certain amount of noise known as the noise floor (heard as hiss, crackles and pops). With quiet musical passages, often this noise floor is louder than the actual music. While some argue that the CD audio standard lacks the fidelity and musicality of analog equipment (failing to mention how expensive top quality analog gear is), there is no denying that for most people, recorded music has become much clearer and more enjoyable to use and listen to.

It's no surprise that computers would come into play in this digital music revolution, as they process information in the same way as CD players: digitally, using binary code. Thus, the merging of digital music and the home PC was inevitable but didn't become common until recently, as the freshman attempts were costly and at times, unreliable. However, music software and hardware has been refined and is less expensive than their predecessors, and sounds better, too. So as musicians, we are now faced with the problem of too many options. Here are some of the better ones.

Let's use this model: a band teacher wants to record his or her spring concert in stereo and put it on a CD. First we need a pair of good microphones. All things being equal, microphones play the most important role in the audio chain. A good microphone makes up for mediocre recording equipment, but a recording with a cheap microphone can never sound good even when used with the finest recording studio gear. Look for microphone brands like Sennheiser, Neumann, Earthworks, Oktava, AKG and Audio Technica. You'll need a pair of identical microphones; one for the left and one for the right channel of the stereo.

Next, you'll need some kind of digital recorder. The most common formats are Digital Audio Tape or DAT, MiniDisc, a stand alone hard disk recorder or your computer's hard drive. You don't necessarily need a stand alone digital recorder, as your computer (which you need anyway) can be used to record as well as edit. An advantage of stand alone digital recorders, though, is that you can archive your recordings without taking up valuable hard drive space. Either way, brands like Tascam, Macintosh, Sony and Yamaha are recommended.

Regardless of which option you choose, you'll need some kind of microphone pre-amplifier which can either be built into the recorder or found externally in a mixer. I would stick with an external microphone mixer like a Mackie, as you'll have more options to adjust the sound, such as EQ.

Once the music is recorded, you have to transfer it into your computer, if you didn't record directly to it already. You'll need some software and hardware to do this. A great stereo editing software, Peak, is made by a company called Bias. Also, Pro Tools by Digidesign is widely used and you can get a free version off of the internet from www.digidesign.com. I recommend audio cards and hardware also by Digidesign and Digigram for stereo capture of digital audio using a Macintosh computer, G3 processor or higher. You'll need a big hard drive, as 44.1 kHz/l6 bit digital audio takes up 10 megabytes of space per minute, with a full length CD taking up 740 megabytes or 3/4 of a gigabyte.

The music must then be saved in one of these file formats: .aiff, sd2, or with a PC, a wav file. These are the formats that CD-R burning software recognizes as a CD audio file. As far as CD burning software, Toast by Adaptec, and for CD-R burners, manufacturers like Yamaha and Philips are good names to stick with. Be sure to use quality CD-R's such as Quantegy or Mitsui.

While we're on the subject of CD-R's, it's important to point out what they are, technically. The name is an abbreviation that stands for Compact Disc-Recordable. It is not identical to a standard store-bought CD. With the store bought version, the binary code that I mentioned earlier is represented by the presence or absence of tiny recessed pits. The laser that reads the disc interprets the reflected light to determine if a pit is or isn't present. With a CD-R, a heated laser burns a shaded spot in a dye mat on the CD-R to trick a CD player's laser into thinking it sees a pit. Essentially, to a CD player, a CD and a CD-R are indistinguishable from one another. Though, older CD players whose lasers may be slightly out of focus may have trouble reading a CD-R.

Along with standard digital recording formats, data compressed formats such as MiniDisc and mp3 are very common. Both use a method of not recording bits considered to be the "least significant;" in essence disregarding information that you probably wouldn't hear anyway. The benefit of this is that you are able to fit more information in a smaller space. You'll notice that MiniDiscs are much smaller than CD's and mp3 files take up a fraction of the hard drive space of a standard CD audio file. Another benefit is faster data transmission. Because mp3 files are smaller, it takes less time to transfer them to other computers via the internet. The trade off is decreased audio quality. If you are mainly listening to music with a narrow dynamic range such as rock or pop, you may never notice this drop in fidelity. But, if you listen to more classical and jazz, you may notice that the fidelity on the quieter passages is diminished; one may describe the sound as "grainy."

For encoding and decoding mp3s from other audio formats for the Mac, I recommend iTunes, a free Apple product. Other applications such as SoundJam do a good job, too. For your IBM PC, WinAmp is recommended. Once you've encoded your mp3, it's easy to email it to other users or post it on a website. It's really very simple and the most common way that music is exchanged on the internet.

So, you want to do it? Cool. Here's a recommended setup with pricing. For the sake of brevity, I've listed only the major components; stands, cables and some other accessories are not listed. This setup does not include the stand-alone digital recorder, as I decided to go with a direct-to-hard disk system for this example. All pricing is suggested retail:

2 Neumann KM 184 cardioid condenser microphones, $749 each, $1458 total.
_ 1 Mackie 1202 mixer, $459
_ l Digidesign AudioMedia III computer interface card, which comes with Pro Tools recording/editing software, $545
* l Power Mac G4/466 MHz processor with 384 MB of RAM and a 30 GB hard drive. $1394 (without monitor).
* 1 Yamaha 16X CD-RW recorder with Firewire connection, $320
* Adaptec Jam CD writing software, $199
* Total cost of system, $4375.
Considering the quality of this system (and that it includes the cost of a computer), the price is reasonable. And, it's a fraction of what it used to cost to get the same quality in your end result. Best of luck