Real World Digital Audio

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With your microphones in place, you’re ready to begin recording to disk.

Double-check the input and output settings in your software first. On Mac

OS X, look for preferences under the application menu (the menu with the

name of the program, like Audacity or Live), and on Windows select File >

Preferences. You can then proceed to record.

Setting Levels

With an input enabled, you’ll need to make sure you have the right input

level. If the signal is too weak, the recording will be too quiet, and amplifying

it to an audible level will add noise. If the signal is too strong or “hot,” it can

cause distortion. By setting your input gain so that the level saturates your

dynamic range without distorting, you’ll get the cleanest possible recording.

This means you need to watch your meters while you’re recording and

make appropriate adjustments as needed (Figure 6.23).

Headroom

Every device has a dynamic range (the amplitudes it can accommodate from

minimum to maximum). On analog equipment, there’s an additional range

above the maximum recommended level (labeled on a meter as 0 dB), up

to the level at which signal significantly distorts or clips. This range is often

colored red on equipment meters. If you’ve ever gone “into the red,”

you’ve exploited the additional range, which is called dynamic headroom

(Figure 6.24).

On analog equipment, you’ll want your meters to read approximately 0 dB

as often as they can, with an occasional excursion slightly “into the red.”

Meters on analog equipment can show a little bit of clipping when the sig-

nal isn’t actually significantly distorting. Digital equipment works differently:

because amplitude is stored as a number and not as a continuous voltage, its

Get the right levels:

Analog:

0 dB, or a little

more or less

Digital:

Approaching

but never crossing 0 dB

Figure 6.23 Watch your

meters (left) to set the right

level. If you need to, adjust

input gain in your hardware

or software, as shown here in

Audacity (right).

For more informa-

tion, see:

Chapters 3–4:

Connect

and configure your

equipment

Chapter 7:

Add signal

processing to sweeten

your sound or add com-

pression and effects

Chapter 10:

Mix sources

together and edit and

arrange your sound

Chapter 13:

Record

on the fly during a

performance

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maximum is really its maximum. Generally speaking, digital equipment

doesn’t have any dynamic headroom; therefore, you’ll have to set your

inputs so that your levels get near the 0 dB threshold without crossing it.

Distortion

“But wait,” you may be saying, “I love distortion!” Odds are, you like ana-

log distortion, a “fuzzy,” warm sound generated by analog equipment

pushed just past its headroom. From distortion pedals to “overdriving”

recorded tracks, musicians have long made use of slight overdrive (pushing a

device just past its amplitude maximum) to get a desired effect.

Digital devices distort differently: instead of rounding off the top of a wave-

form as it passes beyond the amplitude maximum, they slice off the tops of

the sound waves, creating a straight line (Figure 6.25). This result is called

digital clipping, and it’s almost never desirable. In fact, if you want to achieve

analog-style distortion, you’ll need software that can emulate the result.

(See Chapter 7 for more on this effect.) Unless you want the specific and

unpleasant sound of digital clipping, make sure your digital meter never

headroom

0 dB

Figure 6.24 Analog signal

(left) has additional headroom

beyond 0 dB, but anything

above 0 dB on a digital meter

(right) will result in digital

clipping.

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