Junger Audio d02 - Digital Dynamics Processor - Manual (Page 25)

4. FUNCTIONAL DESCRIPTION
The digital audio signal (either an AES/EBU digital input signal or an
analog input converted by the A/D converter) is processed in a Texas
Instruments Floating Point Signal processor with a data width of 32
bits. The use of 32 bit digital audio sample length in calculation
ensures that there is no deterioration in signal quality, even if
AES/EBU digital audio data with the maximum word length of 24 bits
is input into the unit.
The DSP carries out the functions of the dynamics processing, the
linear gain and the emphasis filtering. It measures the input and output
levels and generates data for GAIN CHANGE display. Reading of the
front panel buttons and operation of the front panel display is
performed via a special interface (see also chapter 3.).
One main task of the digital transmission processor d 02 is the
compression of low signal levels. The compression- RATIO expresses
the effects of a change of the input signal in dB on the change of the
output signal in dB.
E.g. a ratio of 2:1 means that a change in input signal of 20 dB causes
a change in output signal of 10 dB. With the choice of a compression
ratio, the intensity of the compression is determined and with it also a
certain compression characteristic (see also fig.2 and fig. 3). The
RATIO parameter is adjusted on the front panel in four steps, from
1.1:1 to 2.0:1. The transition to another characteristic can be carried
out during the running programme. It does not cause any clicking
noises.
The lower the signal level, the higher the gain of the compressor will
be. Independently of compression ratio, the maximum amount of
compression gain can be adjusted so that no inadmissible increase of
background noises (e.g. live atmos, air-conditioning, hum and noise)
may occur during signal pauses.
To set the maximum compression gain press both the RATIO button
and the PROGRAM button simultaneously. A red LED becomes visible
In the compressor gain display , which indicates the maximum value
of compression gain. This value can be changed in 1dB steps over
the range +2dB to +15dB pressing the INC and DEC buttons.
The expander becomes effective when the signal level falls below an
adjustable expander threshold. It is possible to select four thresholds
from -60 dB...-30 dB.
If the level falls below the threshold , the gain is steadily decreased up
to -15 dB. The downward regulation of the expander is achieved just
as quickly as the upward regulation of the compressor, thereby
compensating the resulting increase in signal noise.
For the dynamics functions, particularly the algorithm of the limiter, a
signal delay of approx. 2 ms is built in. This delay makes it possible to
arrange the algorithm of the limiter in such a way that the control
mechanism is activated before maximum level is reached. Within the
rise time of the signal the peak level is recognised and the maximum is
calculated in such a way that full scale level is reached precisely
without causing clipping.
Digital signal processor
compression
Maximum compression
gain
expander
Look ahead limiter
4-3