Aphex 320D Compellor - Manual (Page 16)

320D
Compellor
Page 16 Page 17
6.1 How the Compellor Interfaces
Being an analog processor at the core, the Model 320D contains a high quality 24-bit low
noise codec to receive digital audio and to transmit digital audio. Once the incoming digital
audio is converted by the DAC section, it passes through the Compellor as normal audio. The
audio output is then converted back into digital by the ADC section of the codec.
6.2 I/O and Synchronizing
On the rear panel you can find two AES/EBU digital audio jacks and a push-button switch for
selecting digital or analog audio input. The AES/EBU jacks are standard professional XLR
110 ohm interfaces. There is no word clock input or output. All synchronizing is accomplished
from either the AES/EBU input signal, or the default internal crystal oscillator if no digital audio
input is present.
The output is synchronized to the input sample rate unless there is no digital input, in which
case the internal default sample rate is automatically selected.
6.3 Input Selector
When using a digital audio input, you must select it on the rear panel or the analog input will
be received and the digital input ignored. There is no indication on the front panel of which
input is being used. You should be sure to determine that at the time of installation. This is
probably the first place to look if no audio is being received.
6.4 Processing Thresholds
The Model 320D translates the -20dBFS level of the digital audio source to the 0dB reference
within the Compellor circuits. The digital audio now looks as if its -20dBFS level is the same
as the nominal operating level of an analog input. Properly recorded digital audio is therefore
perfectly fitted into the Compellor’s dynamic range and all processing will be just as an ana-
log signal would receive. The average levels will target around -20dBFS with peaks that will
naturally rise as far (as but seldom as high as) 0dBFS. The selectable peak limiter’s thresh-
old translates to -6dBFS. Thus, no digital audio output peaks will rise above -6dBFS when
the limiter is on. The combination of averaging the level around -20dBFS and holding peaks
below -6dBFS packages the audio perfectly for natural sound quality and for most transfer or
transmission purposes. For example, the digital audio would be ready for direct input to an
MP3 coder, HD recorder, .wav file, etc.
6.4 Bypass Mode
When the front panel Bypass button is pressed, the analog and digital signals are metal con-
tact connected from input to output resulting in a true bypass. The analog line in is tied directly
to the analog line out; the AES3 in is directly tied to the AES3 out. If power fails, the bypass
condition is automatically set, providing a fail-safe feature for mission critical audio chains.
A condition that can cause trouble if not understood is when you are operating the 320D in a
system that feeds analog audio to the Compellor but takes the AES3 digital output. Obviously,
6. Using Digital Audio
ANALOG
CH2
DIGITAL
AES3 INPUT
AUDIO
SOURCE
SELECT
IN 32-96kHz OUT IN
OP
LEVEL
-10
+4
ANALOG
DIGITAL