STA304A

24/30

Table 2. DDX gain

DDX Gain Compression

Since a full-scale output of the GC/Vol block is mapped to full output modulation, any signal exceeding 0 dBFS

at the output of the GC/Vol block will be clipped. The purpose of the compression algorithm is to reduce the

gain of the system when 0 dBFS has been exceeded such that clipping does not take place, thus performing an

output limiting function. This would yield a constant Vout once the gained input exceeds 0 dBFS.

With DDX_GAIN_0 = 1, the output of the GC/Vol block is compared to a threshold set just below 0 dBFS. When

the output of GC/Vol exceeds this threshold the gain of system is reduced following a set time-constant and

gain-reduction rate. This reduction in gain is stored as a variable. If subsequently the output of GC/Vol remains

below a separate lower threshold for a set amount of time the gain is then increased following another time-

constant and gain rate. Thus, seven different constants determine the attack, release, and limiting characteris-

tics of the compression algorithm. These constants have been tuned to sound as musical as possible when the

dynamic range of a recording is being reduced due to 0 dBFS being exceeded.

Figure 15. Compression response to 500 Hz sine at 0 dBFS with gain of +10 dB

DDX_GAIN_0

DDX_GAIN_1

DDXGain

DDX Compression

00

1x

NO

01

2x

NO

1

0

2x

YES

1

1

3x

YES