dbx 128 - INTRODUCTION TO THE dbx 128; Understanding Dynamic Range

4. Set the LEVEL Control so that the ABOVE
THRESHOLD LED lights only on musical peaks, or for
the desired effect.
5. Now press the 128’s TAPE (OUT) REC and PRE
Switches.
6. With your tape machine in Record Ready (Pause)
mode, set its input level controls.
7. Record the tape.
8. To play back the tape just recorded, press the 128’s
TAPE (OUT), PLAY and PRE Switches, and set the
COMPRESS/EXPAND Contro! to the 1.0 position. Play
the tape.
To Play a dbx-Encoded Tape or Disc and Add Peak Limiting
1. Press the 128’s PLAY and POST Switches, and either
the DISC or TAPE Switch depending on the source.
2. Set the ABOVE THRESHOLD/LINEAR Switch to
the ABOVE THRESHOLD position (OUT).
3. Set the COMPRESS/EXPAND Control for the desired
degree of peak limiting (usually 10.0 or higher).
4. Set the LEVEL Control so that the ABOVE
THRESHOLD LED lights only on musical peaks, or for
the desired effect.
5. Play the tape or disc.
INTRODUCTION TO THE dbx 128
A live musical performance is an exciting experience,
the kind of experience that record manufacturers and radio
stations attempt to capture for reproduction in home
listening.
Unfortunately much of the excitement of the original
live performance is lost, even when using the best speakers,
amplifiers, tuners, turntables, and tape machines. The
primary reason for this lack of excitement and realism is
the dynamic range limitations in the recording and
broadcast mediums.
Dynamic Range and Why It Is Important
Dynamic range can be defined as the difference in
sound level, measured in dB, between the loudest and the
quietest passages in music. Acoustical loudness is measured
in decibels of sound pressure level, or dB SPL. The dB
expresses the smallest change in sound level that the average
ear can detect. 0 dB SPL is the threshold of human hearing,
the faintest sound most people can hear at a midrange fre-
quency (1,000 Hz). The loudest sound the average person
can tolerate without physica! pain is approximately 120 dB
SPL (some people can tolerate 130 dB, others leave the
room when the sound level reaches 110 dB). Thus, human
hearing has a maximum dynamic range of about 120 dB SPL.
Noise is the jower restriction of the dynamic range of
most recorded material. Typical sources of noise are phona-
graph disc surfaces, turntable rumble, tape hiss, and FM
broadcast hiss. When the original program’s quietest sounds
are too low in level, they are buried in the noise. ““Rumble”
and “scratch” filters can remove some of this noise, but
unfortunately, they also remove parts of the program. A
simple but effective way to remove or reduce noise
significantly without subtracting anything from the music
has long been sought. One method to avoid noise-imposed
restrictions in the recording and broadcast mediums would