Crown Audio IQ-USM 810 - Manual (Page 25)

Page 25
IQ-USM 810 IQ Digital Processor / Digital Mixer
IQ-USM 810 Reference Manual
5 Technical Information
5.1 Technical Description
Following is a technical description of the operation of
the IQ-USM 810. Refer to the block diagrams on the
following pages for illustration of signal flow.
5.1.1 Audio
Input Section: Each audio input signal first passes
through a balanced filter designed to eliminate RF
interference. The RF filters are a balanced network
of chokes, ferrite beads, and capacitors that attenu-
ate both common-mode and differential-mode sig-
nals above 500 kHz. Optional input isolation
transformers are available.
The balanced signal then enters the input switching
circuit. This circuit can insert a 25-dB pad for line level
signals or apply phantom power to the input terminals
(24VDC through two 2 Kohm resistors). The signal is
filtered again to eliminate lower-frequency RF energy
such as interference from the AM broadcast band.
A discrete preamp stage takes the balanced input
signal and provides 13 to 45 dB of voltage gain
adjustable by a rear panel potentiometer. The
preamp output provides a single-ended voltage out-
put that is then coupled to a single-ended-to- differ-
ential amplifier that also provides the bias offset
needed by the A/D converter.
A 24-bit high-resolution A/D converter samples the
input audio at 48 kHz. The audio processing is set to
provide +20 dBu as full scale, allowing full utilization of
the dynamic range of the converter. Each converter
supplies a two-channel digital audio stream to the
DSPs for processing. One A/D converter acts as a
master to supply sampling clocks to the rest of the
system. A 12.288 MHz oscillator (256 times the 48 kHz
sampling rate) acts as the master clock source.
DSP Processing Section: Four DSP processors
supply all of the digital audio processing in the unit.
Serial digital audio from the input converters are
sent to the DSP board for processing. The input
audio is routed to the two input DSPs. The proces-
sors collect 16 samples of audio, then process the
audio as a “brick” of data. After the input DSPs have
processed the data, they transfer the audio bricks to
shared memory. The two output DSPs then retrieve
the audio from memory and do the required output
processing. The audio is then sent serially from the
DSPs serial ports to the Output board.
The DSP processors have a 30 MHz clock, while
serial digital audio is locked to serial clock (3 MHz)
and frame sync clock (48 KHz) supplied from the
Input board.
An interface to the System Controller board allows
programming of the DSPs, control updates, and meter-
ing information to be passed to the outside world. The
DSPs depend upon the System Controller for program-
ming upon reset or initial power, as there is no nonvola-
tile memory on board.
Output Section: Output serial digital audio from the
DSP board is sent to the output board for conversion
and analog processing. The serial digital audio is com-
prised of two channels of 24-bit signals. Each DAC
converts the audio data stream into two differential
output channels. A differential amplifier filters the
DAC’s audio output and provides single-ended audio
to a gain stage that sets the full-scale output of the
DAC. A single-ended-to-differential stage provides a
50-ohm output. Optional transformers are available for
the Main Outputs.
5.1.2 Control and Interface
System Controller: The System Controller board pro-
vides interface to the outside world as well as providing
all of the program storage and initialization. At reset,
the control processor uses boot code from nonvolatile
flash memory. Program code is then transferred to fast
RAM and the processor begins to run. Each DSP pro-
cessor is then booted via the system interface and
upon successful booting of all the DSPs, audio pro-
cessing begins.
• • • • • Flash Memory Storage: In addition to storing
program code for the control and DSP proces-
sors, flash memory provides storage for all non-
volatile data including presets and settings.
• • • • • IQ Loop: The dual RJ-45 connector allows IN/
OUT connection to an IQ loop. The IQ-USM 810
can act as either an ordinary component or an in-
terface. When acting as an interface, a computer
needs to be connected to the RS232 interface.
• • • • • RS232: When the IQ-USM 810 is in interface
mode, the computer communicates with the IQ-
USM 810 and all components on its IQ loop via
this port. Front Panel control allows setting of the
baud rate, and IQ for Windows software automati-
cally adjusts to this setting. When in the compo-
nent mode, the IQ-USM 810 can still
communicate with the computer through this port.