Art Voice Channel User manual

Voice Channel™
Tube Channel Strip with Digital Connectivity
USER’S GUIDE

IMPORTANT SAFETY INSTRUCTIONS – READ FIRST
This symbol, wherever it appears, This symbol, wherever it appears, alerts
alerts you to the presence of uninsulated you to important operating and maintenance
dangerous voltage inside the enclosure. Voltage instructions in the accompanying literature.
that may be sufficient to constitute a risk of shock. Please read manual.
Read instructions:
Retain these safety and operating instructions for future reference. Heed all warnings printed here and on the equipment.
Follow the operating instructions printed in this user guide.
Do not open:
Aside from one vacuum tube, there are no user serviceable parts inside. Refer any service work to qualified technical
personnel only.
Power sources:
Only connect the unit to mains power of the type marked on the rear panel. The power source must provide a good
ground connection.
Power cord:
Use the power cord with sealed mains plug appropriate for your local mains supply as provided with the equipment. If the
provided plug does not fit into your outlet consult your service agent. Route the power cord so that it is not likely to be
walked on, stretched or pinched by items placed upon or against.
Grounding:
Do not defeat the grounding and polarization means of the power cord plug. Do not remove or tamper with the ground
connection on the power cord.
Ventilation:
Do not obstruct the ventilation slots or position the unit where the air required for ventilation is impeded. If the unit is to be
operated in a rack, case or other furniture, ensure that it is constructed to allow adequate ventilation.
Moisture:
To reduce the risk of fire or electrical shock do not expose the unit to rain, moisture or use in damp or wet conditions. Do
not place a container of liquid on it, which may spill into any openings.
Heat:
Do not locate the unit in a place close to excessive heat or direct sunlight, as this could be a fire hazard. Locate the unit
away from any equipment, which produces heat such as: power supplies, power amplifiers and heaters.
Environment:
Protect from excessive dirt, dust, heat, and vibration when operating and storing. Avoid tobacco ash, drink spillage and
smoke, especially that associated with smoke machines.
Handling:
To prevent damage to the controls and cosmetics avoid rough handling and excessive vibration. Protect the controls from
damage during transit. Use adequate padding if you need to ship the unit. To avoid injury to yourself or damage to the
equipment take care when lifting, moving or carrying the unit.
Servicing:
Switch off the equipment and unplug the power cord immediately if it is exposed to moisture, spilled liquid, objects fallen
into opening, or the power cord or plug becomes damaged during a lightning storm or if smoke odor or noise is noted.
Refer servicing to qualified technical personnel only.
Installation:
Install the unit in accordance with the instructions printed in the user guide.
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Voice Channel
Tube Channel Strip with Digital Connectivity
IMPORTANT SAFETY INSTRUCTIONS – READ FIRST ..........................................................................1
INTRODUCTION....................................................................................................................................4
INSTALLATION .....................................................................................................................................4
AC Power Hookup..................................................................................................................................................................................4
Analog Audio Connections .....................................................................................................................................................................4
FRONT PANEL CONTROLS and JACKS................................................................................................5
Mic Preamp Controls..............................................................................................................................................................................5
Instrument Input .....................................................................................................................................................................................5
Gain Control ...........................................................................................................................................................................................5
Impedance Control .................................................................................................................................................................................5
Pad Switch .............................................................................................................................................................................................5
Phantom Power......................................................................................................................................................................................5
Invert Switch...........................................................................................................................................................................................5
Low Cut Switch.......................................................................................................................................................................................5
Tube Voltage Switch ..............................................................................................................................................................................6
Dynamic Processor Controls ..................................................................................................................................................................7
Threshold Control...................................................................................................................................................................................7
Ratio Control ..........................................................................................................................................................................................7
De-esser Control ....................................................................................................................................................................................7
De-esser Freq. Control ...........................................................................................................................................................................7
Attack Control.........................................................................................................................................................................................7
Release Control......................................................................................................................................................................................8
Gain Reduction LED Meter.....................................................................................................................................................................8
Expander/Gate Switch............................................................................................................................................................................8
Expander/Gate Threshold Control..........................................................................................................................................................8
Semi-Parametric EQ ..............................................................................................................................................................................9
EQ Position Switch.................................................................................................................................................................................9
EQ Bypass Switch..................................................................................................................................................................................9
Output Level Control ............................................................................................................................................................................ 10
Output Level Meters ............................................................................................................................................................................. 10
Sample Rate/Dither Control.................................................................................................................................................................. 11
Optical Output Switch........................................................................................................................................................................... 11
REAR PANEL CONNECTIONS .............................................................................................................12
Mic/Line Input ....................................................................................................................................................................................... 12
Mic Preamp Output .............................................................................................................................................................................. 12
Insert Input ........................................................................................................................................................................................... 12
Balanced Output................................................................................................................................................................................... 12
A/D Main Insert and A/D CH2 Insert..................................................................................................................................................... 12
Wordclock Input and Thru Jacks .......................................................................................................................................................... 12
ADAT Input Jack .................................................................................................................................................................................. 13
Optical Output Jack .............................................................................................................................................................................. 13
S/PDIF Output Jack.............................................................................................................................................................................. 13
AES/EBU Output Jack.......................................................................................................................................................................... 13
USB Jack.............................................................................................................................................................................................. 13
APPLICATIONS ...................................................................................................................................14
Bypassing Components Of The Voice Channel™................................................................................................................................ 14
Optimizing The Preamp For Lowest Noise........................................................................................................................................... 14
Utilizing Pre/Post Compression EQ...................................................................................................................................................... 14
WARRANTY INFORMATION................................................................................................................15
SERVICE .............................................................................................................................................16
SPECIFICATIONS................................................................................................................................17
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LIST OF FIGURES
FIGURE 1 – Preamp section ................................................................................................................. 6
FIGURE 2 – Dynamics Section.............................................................................................................. 6
FIGURE 3 – Equalizer Section .............................................................................................................. 9
FIGURE 4 – Signal Flow Block Diagram ............................................................................................. 10
FIGURE 5 – Output Section ................................................................................................................ 11
FIGURE 6 – Rear Panel ....................................................................................................................... 11
FIGURE 7 – Wordclock Termination ................................................................................................... 13
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INTRODUCTION
The ART Voice Channel™ is the answer to your recording and computer audio interface needs. Our second-
generation discrete Class-A microphone preamp provides clean quiet gain while maintaining incredible
transparency. A powerful dynamics processor subtly controls transients and noise of the most demanding
sources. The ART Voice Channel’s semi-parametric EQ offers wide tune-ability and can be patched before OR
after the dynamics processor. Separate insertion jacks allow you to use your favorite external signal
processing gear immediately after the Mic preamp and before the EQ and dynamics processor. Another patch
point exists just before the A/D converters. Choose between a wide range of outputs including balanced analog
output, 44.1 KHz to 192 KHz AES/EBU, S/PDIF, ADAT and USB. Both analog and digital meters provide a
detailed indication of audio levels.
INSTALLATION
The ART Voice Channelmay be used in a wide variety of applications and environments. In a rack-
mountable, all-steel enclosure, the unit is designed for continuous professional use. Mounting location is not
critical, however for greater performance reliability we recommend that you not place the unit on top of power
amps, or other sources of heat and/or strong magnetic fields. The tube circuitry needs about a minute to “warm
up” and stabilize from a cold power up.
AC Power Hookup
The ART Voice Channelhas an internal power supply. Only connect the unit to mains power of the type
marked on the rear panel. The power source must provide a good ground connection, and the ground pin on
the mains plug should never be defeated.
Analog Audio Connections
Audio connections to and from the Voice Channelare:
Front panel balanced combo input: [XLR] Pin 2 = Hot (+), Pin 3 = Cold (-), Pin 1 = Ground
[1/4”] Tip = Hot (+), Sleeve = Ground
Rear panel balanced combo input: [XLR] Pin 2 = Hot (+), Pin 3 = Cold (-), Pin 1 = Ground
[1/4”] Tip = Hot (+), Ring = Cold (-), Sleeve = Ground
Rear panel balanced 1/4” output: Tip = Hot (+), Ring = Cold (-), Sleeve = Ground
Rear panel 1/4” insert input: Tip = Hot (+), Sleeve = Ground
Mic Preamp Output: Tip = Hot (+), Sleeve = Ground
A/D Main & A/D CH2 Inserts: Tip = Input, Ring = Output, Sleeve = Ground
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FRONT PANEL CONTROLS and JACKS
Mic Preamp Controls
The Voice Channel™ input consists of a discrete Class-A differential preamp. The circuit is optimized for low
impedance microphones as well as line level signals. Up to 60dB of gain is available from this stage. The
output can be inverted using the INVERT switch.
The impedance of the front and rear XLR inputs is continuously variable for fine-tuning the preamp to a wide
variety of mics. Phantom power is available on the XLR inputs as well.
A selectable low-cut filter removes rumble, wind noise, and pops, thereby increasing clarity.
Instrument Input
The 1/4” T/S jack on the front panel provides a high impedance unbalanced input, and when used,
automatically switches off the mic pre-amp. (The rear combo jack’s 1/4” T/R/S balanced input is lower
impedance and is part of the mic pre-amp. The rear jack is not intended to be used with high impedance
microphones or instruments.) NOTE: When using the INSTRUMENT INPUT, the PAD switch is disabled and
does NOT affect the gain.
Gain Control
This control adjusts both the mic pre-amp gain as well as the instrument input gain. The gain marked applies
to the mic pre-amp without the PAD switch depressed. The instrument input gain markings are on the right side
of the slash (/). Refer to the APPLICATIONS section to learn how to optimize the gain control for low noise
operation.
Impedance Control
This knob sets the load impedance at the front and rear panel XLR inputs of the Voice Channel™. Use the
IMPEDANCE CONTROL to subtly tune the sound of your microphone. Various microphones will change their
sound at differing load impedances. The correct setting is subjective. Adjust this control to personal taste.
Pad Switch
This switch reduces the mic pre-amp gain by up to 20dB to prevent clipping when high level mic, or line level
signals are applied to the balanced XLR or 1/4” T/R/S inputs. This switch does NOT affect the 1/4” T/S front
panel INSTRUMENT INPUT.
Phantom Power
The switch safely applies +48Volt phantom power to the XLR inputs. Use phantom power only when the
microphone that you are using requires it. Doing so will extend the life of the Voice Channelas well as
reducing the possibility of shock hazard.
Invert Switch
This switch selects the output phase of the Voice Channel™. There is a 180 degree phase shift through the
Voice Channel™ when lit.
Low Cut Switch
This switch inserts a 100Hz 6dB/Oct. Low-Cut filter into the signal path. The filter is designed to remove
rumble, pops, and wind noise, yet still sound natural.
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FIGURE 1 – Preamp section
Tube Voltage Switch
The vacuum tube preamp section can be adjusted to run at two different plate voltages. Refer to Figure 2 for
the location of the switch.
Choose the “NORMAL” setting for adding warmth to the input signal. This setting has an increased amount of
tube saturation at higher signal levels.
Choose the “HIGH” setting to increase overall gain, headroom, and bandwidth.
NOTE: The change between tube voltage modes is gradual, taking 10 to 20 seconds to be fully activated.
FIGURE 2 – Dynamics Section
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Dynamic Processor Controls
The ART Voice Channel™ dynamics section consists of an above threshold Compressor/Limiter with De-
esser plus a selectable Expander/Gate. The attack and release controls allow a wide range of adjustment while
the complex detector assures fast response without distortion. The De-esser is frequency tunable.
Threshold Control
This control sets the level, above which the Compressor/Limiter in the Voice Channel™ starts to act on the
input signal. As the control is turned clockwise, more input signal is required to begin reducing gain. The
compression action can be seen in the Gain Reduction LED meter.
Ratio Control
The RATIO control sets the amount of gain reduction that takes place based on how far the input signal is
over the threshold level (set by the THRESHOLD control). When the control is fully counterclockwise, the
Compressor/Limiter is OFF.
A good starting point for vocals is 2.5:1.
To have the unit act as a limiter, set the RATIO control to 20:1.
De-esser Control
The DE-ESSER control sets how much more the gain is reduced at high frequencies when using the
Compressor/Limiter. The most common application is reducing sibilance when compressing vocals. When fully
counterclockwise, the De-esser function is OFF. As the control is turned clockwise, high frequency material is
compressed more than mid and low frequency material.
De-esser Freq. Control
This control selects which high frequencies the DE-ESSER acts upon. Turned fully counterclockwise, the
DE–ESSER acts on the upper mid-range. When set fully clockwise, only the highest frequencies are reduced
more during de-essing compression. Center the DE-ESSER FREQ. control as a starting point for vocal work.
Attack Control
The ATTACK control sets the time it takes the Compressor/Limiter to respond to increases in signal level (by
reducing gain). You can use this control to shape the “front end” of the dynamics envelope.
One example is to listen to a snare hit and adjust the attack control. A short attack makes the snare sound
“thin”. As the attacks go longer (and the knob is turned clockwise) you should hear more of the thump in the
compressed snare. The downside is that this creates an overshoot, (a large transient), the length of which is
the time set by the ATTACK control.
Overshoots less than 1 msec are very hard to hear even when they are clipped. If the attack is set too fast,
the gain may be reduced too much and thereby create a “pumping” sound1. One way to eliminate this is to use
the LOW CUT filter to remove plosive sounds in vocals that can make the detector overreact.
1“Pumping” in a Compressor/Limiter sounds like the signal is muted when it shouldn’t be.
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Release Control
The RELEASE control sets the time the Compressor/Limiter takes to increase the gain after the input level
drops.
Longer settings maintain the dynamics of the input signal, while shorter settings reduce the dynamics.
Shorter settings will also increase the apparent reverberation, and at extreme gain reduction settings, lead to
“breathing” artifacts2
Gain Reduction LED Meter
The GAIN REDUCTION meter displays the Compressor/Limiter’s attenuation action. The meter covers a very
large range while offering high resolution.
The large yellow LED at the right-hand end of the meter indicates Expander or Gate action. The brightness of
the LED indicates the amount of gain reduction for the Expander function. Since the Gate is either ON or OFF,
there is no brightness variation.
Expander/Gate Switch
This switch allows the selection of the Expander or the Gate functions. Both are useful in reducing unwanted
background noise in the audio signal.
In the “OUT” position the Expander function is selected. Use this mode to gradually reduce background noise
and maintain some of the input dynamics. This is useful for instruments with gradually decaying amplitude
envelopes.
Depress this switch to select the Gate mode. This mode quickly cuts off the noise as the input signal drops.
Expander/Gate Threshold Control
The Expander/Gate action begins below the level indicated by the EXPANDER/GATE THRESHOLD control.
The EXPANDER/GATE THRESH. LED in the GAIN REDUCTION display will light when the Expander or Gate
attenuates the input signal.
The Expander/Gate Threshold detector has built-in hysteresis, which causes the unit to trigger “ON” at a
higher level than the level required to trigger back to the “OFF” state.
The Expander slope is about 1:1.5. This is subtle enough to maintain the decay envelope of the source
material and still lower the noise as the input signal drops. The EXPANDER/GATE THRESH. LED will light
dimly for the first 5dB of gain reduction, and then glow brightly as the attenuation increases above this level.
The Gate function has an intelligent detector with a fast “attack” and “release”, coupled with a program
dependant “hold”. The hold time is longer for sustained passages and shorter for transients. As the input drops
below the threshold and the input signal is muted, the EXPANDER/GATE THRESH. LED lights brightly.
You can turn off the Expander/Gate function by setting the THRESHOLD control fully counterclockwise to
“OFF”.
2“Breathing” is the sound of the Compressor/Limiter turning up the gain so quickly you can hear breathing noises between words
during vocal processing.
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Semi-Parametric EQ
The ART Voice Channel™ offers a four-band semi-parametric equalizer. The EQ can be bypassed as well as
positioned before or after the dynamics processing section. Each band has + 15dB of control range.
The High and Low EQ bands are shelving type with a switch selectable turnover point.
The two Mid bands can be continuously tuned over a five octave range.
FIGURE 3 – Equalizer Section
EQ Position Switch
The EQ POSITION switch allows you to connect the EQ before or after the dynamics processing block. This
is useful in cases where the input signal needs a great deal of EQ before the Compressor/Limiter processes it.
One example of using the EQ in the “PRE” position is using the LOW EQ control as a tunable low frequency
cut, supplementing the LOW CUT filter switch.
Refer to Figure 4 for the block diagram of the Tube Channel. Note that the Mic preamp insert jack function is
located before the EQ position switch.
EQ Bypass Switch
This switch allows you to instantly set the EQ completely flat without loosing the current EQ settings.
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