Rane RPM 88 - Manual (Page 6)

Manual-4
Audio Connections
As a safety precaution, turn all devices (especially power amplifi-
ers) OFF when making connections. Doing so gives you a chance
to find and correct wiring mistakes and prevent damage to your
amplifiers, speakers, ears, etc.
Analog Inputs and Outputs
The RPM 88 has eight balanced analog Inputs and eight bal-
anced analog Outputs.
For each Input or Output Euroblock connector:
• Connect the (positive) audio line to the ‘+’ terminal.
• Connect the (negative) audio line to the ‘–’ terminal.
• Connect the cable shield to the ground terminal.
For those installations where the RPM 88’s internal shield-
to-chassis connection causes interference, connect each shield
directly to the chassis PEM nut located above each Euroblock
connector, keeping the shield wrapped around the audio conduc-
tors as much as possible.
For optimum Electromagnetic Interference (EMI) immunity,
connect the shields at both ends of the cable. See the RaneNote
“Sound System Interconnection” for more information on system
connections and proper grounding practices.
Analog Input Stage
Each analog input uses a two-stage gain approach. The first stage
contains a software controlled analog line/mic pad and switch-
able-gain preamp. The second stage contains a Digital Trim
control located immediately after the A/D converter.
Input Clipping
If you’ve set the Analog Gain so the input stage is not clipping,
it is not possible to clip the A/D converter, since there is no addi-
tional gain between the initial input stage and the A/D convert-
er. The Digital Trim control, located after the A/D converter, can
be set to clip the signal to your heart’s content, so adjusting this
trim to provide the hottest signal to the DSPs without clipping is
the most important step when setting up gain structure. For this
reason, a dedicated meter displaying the signal level being passed
to the DSPs is provided in each Analog Input block.
If the DSPs are working with a clipped signal, the audio is (as
expected) distorted and none too pretty, but it is not a drastic,
damaging sound. And while it’s technically possible to write a
DSP algorithm to emulate the glorious clipping distortion of
vacuum tubes, it’s not particularly useful for an installed sound
system, where the DSP power could be put to better use remov-
ing that annoying 500 Hz feedback from the Pope’s podium mic.
Plus, they don’t yet make DSP chips with gold-plated substrates
for those fecund highs and that moist, supple midrange.
Analog Output Stage
Each analog output also uses a two-stage gain approach, which
differs slightly from that of the analog input stage. The first stage
is a Digital Trim control located immediately before the D/A
converter. The second stage is an analog trim control located im-
mediately after the D/A converter. Attenuation is handled in the
analog domain, while boosting (when the incoming digital signal
is low) is handled in the digital domain. Boosting and attenuat-
ing using this two-stage approach helps maintain the RPM 88’s
excellent noise performance.
Digital (AES3) Input and Output
AES3 is a popular 2-channel (stereo) digital audio interface com-
monly found on professional digital audio equipment (digital
mixers, DAT machines, etc.). Each channel of the AES3 digital
stream is treated independently within the RPM 88.
See the RaneNote “Interfacing AES3 and S/PDIF”, available
from Rane’s web site (www.rane.com/library.html), for more
information about interfacing consumer S/PDIF gear to the
professional AES3 standard.
Use the AES3 I/O to:
• Connect multiple RPM 88s together to create a 2-channel
digital “bus” between devices.
• Connect directly to the AES3 output of a digital mixing
console.
• Connect directly to the AES3 input of a digital recorder.
• Connect to an external A/D or D/A converter, effectively add-
ing two more analog inputs or outputs.
Incoming Sample Rate and Word Length
The AES3 input has a built-in sample rate converter capable of
accepting incoming sample rates up to 96 kHz. Sample rates ex-
ceeding the RPM 88’s internal 48 kHz sample rate are automati-
cally downsampled. Word lengths up to 24-bits are accepted.
Outgoing Sample Rate and Word Length
The AES3 output uses a fixed 48 kHz sample rate and 24-bit
word length.
Control Connections
Versatile Input Port (VIP)
Eight logic input pins are provided, each capable of accept-
ing DC voltage between 0 and 5 volts. VIP pins are used with
contact closure switches for Preset recall, or with potentiometers
for remote Level control. The functionality (Preset recall versus
control) of each pin is assignable as part of the Device Configu-
ration.
• The maximum allowable voltage on any VIP pin is 5.3 VDC.
• Use of twisted pair cable is recommended for better noise
immunity.
• If an external device is used to generate a 0 to 5 volt signal,
connect the ground of the external device to the GND pin of
the VIP.