Text preview for : Focusrite.TwinTrak.ug.pdf part of Focusrite Platinum 10 TwinTrak Pro Hand drawn PCB layout/wiring, and deduced schematic, for the Channel 2 MIC input stage up to the LINE/INST switches.
Took ages to trace this, while fixing this unit (R59 open, causing very low MIC gain).
Channel one circuit will be identical, and PCB layout looks similar.
Hope this is useful to others working on this model. I think the input circuit is similar in a lot of other Focusrite mic preamps, so may help with other models too.
Back to : Focusrite.TwinTrak.ug.pdf | Home
ENGLISH
CONTENTS IMPORTANT SAFETY INSTRUCTIONS
CONTENTS ......................................................................................................................1 Please read all of these instructions and save them for future reference. Follow all
IMPORTANT SAFETY INSTRUCTIONS...................................................................1 warnings and instructions marked on the unit.
INTRODUCTION ...........................................................................................................2
· Do not obstruct air vents in the rear panel. Do not insert objects through any
GETTING TO KNOW THE UNIT ...............................................................................2 apertures.
REAR PANEL CONNECTIONS ...................................................................................3 · Do not use a damaged or frayed power cord.
GETTING STARTED ......................................................................................................3 · Unplug the unit before cleaning. Clean with a damp cloth only. Do not spill
liquid on the unit.
FACILITIES AND CONTROLS .....................................................................................4 · Ensure adequate airflow around the unit to prevent overheating. As this is a Class
DISCRETE CLASS A PRE-AMP ...............................................................................4 A unit, we recommend leaving a blank 1U panel above the unit to aid ventilation.
MID SCOOP EQ ..........................................................................................................5 · Unplug the unit and refer servicing to qualified service personnel under the
following conditions: If the power cord or plug is damaged; if liquid has entered
OPTICAL COMPRESSOR.........................................................................................6
the unit; if the unit has been dropped or the case damaged; if the unit does not
OUTPUT LEVEL .........................................................................................................6 operate normally or exhibits a distinct change in performance. Adjust only those
LATENCY FREE MONITORING ...........................................................................7 controls that are covered by the operating instructions.
MONITOR LEVELS....................................................................................................7 · Do not defeat the safety purpose of the polarised or grounding-type plug. A
polarised plug has two blades with one wider than the other. A grounding type
LATENCY FREE MONITORING CONNECTIONS ...........................................8 plug has two blades and a third grounding prong. The wider blade or the third
DIGITAL........................................................................................................................8 prong is provided for your safety. When the plug provided does not fit into your
DIGITAL CONNECTIONS .......................................................................................8 outlet, consult an electrician for replacement of the obsolete outlet.
DIGITAL OUTPUT OPTION ........................................................................................9
WARNING: THIS UNIT MUST BE EARTHED BY THE POWER CORD.
MIC PRE-AMP INPUT IMPEDANCE..........................................................................9
UNDER NO CIRCUMSTANCES SHOULD THE MAINS EARTH BE
VARIABLE IMPEDANCE: IN DEPTH EXPLANATION......................................9 DISCONNECTED FROM THE MAINS LEAD.
IMPEDANCE SETTING QUICK GUIDE..............................................................10
WORDCLOCK ...............................................................................................................10 This unit is supplied pre-configured to operate only at the voltage indicated on the
rear panel. Ensure correct mains voltage is available and the correct fuse value is fitted
WORKING WITH STEREO SIGNALS ......................................................................10
before connecting to the mains supply. To avoid the risk of fire, replace the mains fuse
A BEGINNER'S GUIDE TO COMPRESSION ..........................................................12 only with the correct value fuse, as marked on the rear panel. The internal power
FREQUENTLY ASKED QUESTIONS........................................................................14 supply unit contains no user serviceable parts. Refer all servicing to a qualified service
TROUBLESHOOTING .................................................................................................16 engineer, through the appropriate Focusrite dealer.
CONTACTING US ........................................................................................................16
RACK VENTILATION: AS THE TWINTRAK PRO IS A CLASS A
TWINTRAK PRO AND YOUR STUDIO.................................................................81 DEVICE, PLEASE ENSURE IT IS PLACED TOWARDS THE BOTTOM
SPECIFICATIONS ..........................................................................................................89 OF YOUR EQUIPMENT RACK, WITH SUFFICIENT SPACE ABOVE
FOCUSRITE DISTRIBUTOR LIST............................................................................91 AND BELOW FOR VENTILATION.
1
ENGLISH
INTRODUCTION
There are 3 separate signal processing sections within each of TwinTrak Pro's two
TwinTrak Pro is an extremely focused and cost-effective stereo processor; the perfect record paths:
`analogue plug-in' for any modern audio recording studio. It provides all the necessary
tools to: · Discrete Class A Pre-amp
· Mid Scoop EQ
· Track stereo or dual mono signals · Optical Compressor
· Process stereo or dual mono signals
· Monitor signals within the mix via a simple hands-on control surface To ensure the cleanest signal path to your recording medium both the MID SCOOP
· Carry out essential processing for mixdown purposes EQ and the OPTICAL COMPRESSOR can be individually switched out of the
audio path (`hard bypassed') when not in use.
See TWINTRAK PRO AND YOUR STUDIO on page 17 for further information
on how TwinTrak Pro can enhance your current studio setup.
GETTING TO KNOW THE UNIT
TwinTrak Pro combines two facility-enhanced Class A pre-amps with a custom
optical dual mono/stereo compressor. In addition, TwinTrak Pro boasts a number of Whilst you are getting to know the unit, use it with a sound source with which you
unique features above and beyond its pre-amps and compressors, including variable are familiar. For example, you could run a favourite CD through the unit, as working
input impedance, instant `air', mid-scoop EQ and a latency free monitoring section with a familiar track makes interpretation of the results easier. Note, however, that
that boasts enhanced routing and control options, featuring a DAC as standard, as well most tracks are already compressed for CD, so you may find it hard to hear the results
as an optional ADC. of using the Optical Compressor. If this is the case, try using `dry' samples instead, or
record your own track uncompressed, then play it back through TwinTrak Pro.
When recording, do not assume you must route your signal through a mixing desk:
simply connect your sources to TwinTrak Pro and connect the outputs of TwinTrak
Pro directly into your sound card or recording device. This form of direct recording
will ensure you record the cleanest signal at the highest quality, since it removes the
possibility of noise being added to the signal when routing through a mixer.
Indeed, with many engineers now mixing within the DAW, and with TwinTrak Pro
providing you with two comprehensive record channels and latency-free monitoring,
you may no longer need your mixing desk, saving precious studio space.
2
ENGLISH
REAR PANEL CONNECTIONS GETTING STARTED
1. Ensure that nothing other than the mains supply is connected to your TwinTrak
Pro, then switch it on via the POWER switch on the right hand side of the unit. If
your unit is permanently connected to a patchbay, ensure audio is not being fed to any
connected speakers, thus avoiding any 'turn-on' speaker pops.
2. Connect the appropriate OUTPUTS (either +4 dBu balanced XLR or 10 dBV
unbalanced jack) from both channels on the rear panel of the TwinTrak Pro to your
recorder or audio interface. If using the digital output option, connect the digital
output to the digital input of your recorder or audio interface. See page 9 for more
information on the TwinTrak Pro digital output option. If using your digital input,
CHANNEL 1 (L) and CHANNEL 2 (R) - Each channel has a balanced (+4 connect the digital input to the digital output of your recorder or audio interface.
dBu) TRS jack LINE INPUT connector on the rear panel, with balanced XLR MIC
INPUT and unbalanced 1/4" jack INSTRUMENT INPUT connectors located on 3. Connect the MONITOR inputs to your desk or sound card output and connect
the front fascia. The TRS jack INSERT connectors on the rear panel allow an the MONITOR outputs to your monitor amplifier inputs or external powered
additional processor to be inserted into the signal chain between the pre-amps and the monitor speakers.
other processing sections of the unit. OUTPUTS are provided on both balanced (+4
dBu) XLR and unbalanced (-10 dBV) 1/4" jack connectors. There is also a TRS jack 4. Ensure that each processing section is switched out (IN switch disengaged and
COMPRESSOR SIDE-CHAIN INSERT connector see page 6 for details. unlit).
FX - The balanced (+4 dBu) TRS jack FX SEND and FX RETURN connectors 5. Connect your input sources as required. Microphones can be plugged into the XLR
allow effects units to be used in the monitor section without affecting what is being MIC INPUTs on the front fascia. If you wish to connect a line-level source (to use the
recorded. See LATENCY-FREE MONITORING and MONITOR LEVELS on TwinTrak Pro's dynamics processing when mixing down, for example) connect this to
page 7 for further details. the TRS LINE INPUTs on the rear panel. Alternatively, you may connect electric
guitars or similar instruments to the INSTRUMENT INPUTs via the unbalanced
LATENCY-FREE MONITORING - The balanced (+4 dBu) TRS jack 1/4" jack inputs on the front fascia. Be sure to select the right gain option (HIGH
MONITOR INPUT connectors allow the output of a stereo mixer or sound card to GAIN switched in for instruments that require extra gain, such as passive instruments)
be connected to the TwinTrak Pro's LATENCY-FREE MONITORING system. - see page 5 for more on the HIGH GAIN setting.
There are also balanced (+4 dBu) TRS jack HEADPHONES MIX connectors and
balanced (+4 dBu) XLR MONITOR OUTPUT connectors, allowing the TwinTrak 6. Check that the correct input is selected in the DISCRETE CLASS A PRE-AMP
Pro to be connected to an external monitoring system. See LATENCY-FREE section. If recording a line level source connected to the rear panel LINE INPUT,
MONITORING CONNECTIONS on page 8 for further details. ensure the LINE switch is engaged. If recording an instrument through the front
INSTRUMENT INPUT, ensure the INST switch is engaged. The MIC LED will
DAC INPUT - The co-axial (RCA phono) S/PDIF connector allows a digital illuminate if neither the INST or LINE switches are engaged. The MIC input is then
signal to be fed to either the monitoring section, or to the line input for further automatically selected.
processing. This section also features a BNC wordclock out connector. See DIGITAL
CONNECTIONS on page 9 for further details. 7. Make sure the phase reverse (Ø) and HPF ( ) switches are disengaged and that the
LEVEL control is fully counter-clockwise.
ADC OUTPUT - An optional ADC is available and can be retrofitted at any time.
This provides an S/PDIF output as well as a BNC wordclock in connection. See 8. If using a condenser or dynamic microphone that requires phantom power, engage
DIGITAL OUTPUT OPTION on page 9 for further details. the +48V switch. If you are unsure whether your microphone requires this phantom
power, refer to its user guide. Phantom power can damage some microphones,
especially ribbon microphones, so beware.
3
ENGLISH
microphone requires phantom power, refer to its user guide before connecting, as it is
9. Increase the LEVEL control, checking the input level meter LEDs and ensuring the possible to damage some microphones (most notably ribbon microphones) by
red O/L LED does not illuminate, except occasionally and briefly when the loudest providing them with phantom power.
signal is present. Note that the input is graded in dBfs, so a level of around 0dBu will
only illuminate the first 2 LEDs. AIR (switch) - This provides a pleasant boost in the high-end frequencies
See www.sospubs.co.uk/sos/may00/articles/digital.htm for more about dBu (affecting the MIC INPUT only). The exact boost frequency is dependent upon the
and dBfs. microphone being used. This effect can simply be described as 'adding air' to the signal
and enables the pre-amp to recreate the open and airy qualities of more expensive
10. If using a microphone, ensure that the microphone placement is at its best. Before transformer-based pre-amps.
you start recording, alter the position of the microphone until you get as close as
possible to the sound you want. Note that moving the microphone may have an effect IMPEDANCE (knob) - Rotating the IMPEDANCE control alters the input
on the level of the signal entering the TwinTrak Pro, requiring an alteration to the impedance of the mic pre (affecting the MIC INPUT only). By adjusting the
LEVEL setting. impedance of the TwinTrak Pro's discrete Class A transistor input, the performance of
both the pre-amp and the microphone connected can be tailored to set the desired
11. You can now eliminate any problematic mid frequencies by using the MID level and frequency response. For more information see the MIC PRE-AMP INPUT
SCOOP EQ section. See page 5 for more information on the MID SCOOP EQ. IMPEDANCE section on page 9.
12. The OPTICAL COMPRESSOR will help control the dynamics of the signal INSTRUMENT INPUT - These are high impedance 1/4" jack inputs that allow
passing through the unit. See page 6 for more information on the OPTICAL you to connect an electric guitar or bass guitar to the unit without loading the pickups,
COMPRESSOR. and without the need for a DI box.
FACILITIES AND CONTROLS
POWER (switch) - Turns the unit on. We recommend that the unit be powered
up before connecting to any equipment that it is feeding, to avoid clicks or thumps
which may harm output devices.
DISCRETE CLASS A PRE-AMP
This part of the unit is a pre-amplifier, used to amplify the incoming signal being fed
to the MIC INPUT or INSTRUMENT INPUT to a suitable level before any further
processing is applied.
MIC INPUT - This is an XLR connector that allows you to connect a microphone
to the unit. If using the TwinTrak Pro's mic pre and feeding the output into a mixing
console, bypass the console's own mic pre and connect the TwinTrak Pro output to
the mixing console channel's line input. This will mean the superior TwinTrak Pro
mic pre is used to process the signal, avoiding unwanted noise, distortion and
colouration from an inferior mic pre. Always avoid routing the TwinTrak Pro's mic
pre into a second mic pre, as this will produce greatly inferior results.
+48V (switch) - This provides +48V of phantom power for condenser
microphones (affecting the MIC INPUT only). If you are unsure whether your
4
ENGLISH
HIGH GAIN (switch) - This provides an extra 20 dBu of gain which is ideal example, when recording a snare drum with two microphones (one on the top of the
when working with passive instruments. The LEVEL knob can then be used to adjust snare, the other on the bottom) they will be out of phase.
the gain level more accurately. To assess if HIGH GAIN is required, connect a sound
source with the input LEVEL set to -10. Gradually increase the input level. If you are Use the phase reverse switch to reverse the phase on one of the microphones (but not
unable to get the level you require, even with the trim at +10, bring the LEVEL back both) - it normally doesn't matter which microphone you reverse. However, if the
to -10 and engage the HIGH GAIN switch. Now return to the LEVEL and adjust source is being picked up by another microphone (for example, by an ambient
accordingly. microphone) then you need to ensure that you do not put your two close
microphones out of phase with the ambient microphone.
INSTRUMENT (switch), LINE (switch) and MIC (LED) - With
TwinTrak Pro, you can select whether to record at mic, line or instrument level, all If you think two signals are out of phase, you can listen for phase as follows:
from the front fascia. If you wish to record via the INSTRUMENT INPUT, simply 1. On your monitoring system, pan one signal left and the other right.
engage the INST switch. Once selected, it will illuminate. If you wish to record via 2. Set the monitoring to mono.
the LINE INPUT, the INST switch must be disengaged, then simply engage the 3. Use the phase switch to reverse the phase on one of the signals. When the two
LINE switch. It too will illuminate when engaged. The MIC LED will illuminate if signals are in phase, the signal sounds bigger.
neither of the other input options are selected, and the MIC input will be selected
automatically. (HPF switch) - This is a high-pass filter, which removes unwanted low
frequencies such as stage rumble via microphone stands, or `proximity effect' (where
LEVEL (knob) - This is used to set the optimum input signal level. Connect an low frequencies are over-emphasised when using certain types of microphone at close
input signal to the unit, ensuring that the LEVEL control is set fully counter- range). The cut-off frequency is 75 Hz with a slope of 18 dB per octave.
clockwise, and increase the LEVEL control whilst observing the LED signal meter.
The red O/L (overload) LED may light occasionally, but only if the input signal gets INSERT (rear panel connector) - The INSERT connectors on the rear
particularly loud. If the O/L LED stays on continuously for any period, or you hear panel allow additional external signal processors to be inserted into the signal chain
the unit distort during loud peaks, you should reduce the input LEVEL. between the pre-amp and the other processing sections of TwinTrak Pro. This insert is
a single TRS jack, configured as tip = send, ring = return. A specially configured lead
Note that the meter is calibrated to read 0 dBfs at the top of the meter - this has been (not provided) will allow you to connect this single point to both the input and output
set up to enable simple metering when recording to digital media. The best level to set of an external signal processor, bringing the signal back to the point from which it was
for recording depends on your recording medium. If recording to an analogue sent after the benefit of external processing.
medium like tape, where extra headroom is required, a level of 18 dBfs will give a
suitable +4 dBu equivalent output. If recording to digital media, you may wish to MID SCOOP EQ
record at a higher level, peaking at e.g. 4 to 6 dBfs. Confused? Visit
www.sospubs.co.uk/sos/may00/articles/digital.htm for further illumination. The MID SCOOP EQ section allows you to cut the selected frequency by up to 12
dB. This can be useful for removing troublesome frequencies when recording acoustic
With the MIC INPUT selected, the LEVEL control provides 0 dB (fully counter- instruments and bass guitars.
clockwise) to +60 dB (fully clockwise) of gain. With the INSTRUMENT INPUT
selected, the LEVEL control provides 0 dB to +20 dB of gain, with an additional 20
dB of gain available with the HIGH GAIN switch engaged, i.e. +20 dB to +40 dB.
With the LINE INPUT selected, the gain is adjustable from 10 dB to +10 dB.
Setting the LEVEL control to the 12 o'clock position will not alter the gain of a line
level input signal.
Ø (Phase Reverse switch) - This allows the phase of the input signal to be
reversed. When recording a single source using more than one microphone, it is
possible for the signals from the microphones to be out of phase, which affects the IN (switch) Switches the MID SCOOP EQ into the signal path. When engaged,
quality of the recording since signals that are out of phase tend to sound `thin'. For the red LED in the switch cap is lit.
5
ENGLISH
CUT FREQUENCY (knob) Adjusting the CUT FREQUENCY knob allows SLOW ATTACK (switch) - When engaged (in), selects a slower attack time,
the centre frequency to be `tuned in'. The frequency range is 120 Hz to 2 kHz. which allows more of the transient peaks of the signal through the compressor. This
can help retain a sense of the original signal's dynamics when compressing heavily. For
DEEP (switch) When engaged (in), the DEEP switch increases the depth of cut example, this can be useful to allow compression of a snare drum without losing the
from 6 dB to 12 dB. initial `crack' of the drum stick striking the snare skin.
RELEASE (knob) - Determines the time taken for the gain reduction to return to
OPTICAL COMPRESSOR normal once the signal drops below the threshold. The faster the release, the louder the
signal appears to be.
The OPTICAL COMPRESSOR acts like an automatic volume control, turning
down the volume of a signal if it gets too loud. This reduces variation between loud HARD RATIO (switch) - When engaged (in), selects a higher compression
and quiet passages, as it automatically reduces the gain when the signal exceeds a given ratio, which gives a very flat, compressed sound. Do not use the HARD RATIO
volume, defined as the threshold. Using the OPTICAL COMPRESSOR helps to switch if you want to maintain most of the original dynamics.
`even out' a performance, stopping a signal from clipping and/or disappearing in the
mix. See page 12 for a BEGINNER'S GUIDE TO COMPRESSION. HARD KNEE (switch) - When engaged (in), selects a harder attack mode,
which gives a very punchy and more obviously compressed sound.
MAKEUP GAIN (knob) - Sets the output volume of the compressed signal.
Since compressing a signal makes it quieter, use the MAKEUP GAIN control to
restore the signal to its original volume. Compare the volume of the original and the
compressed signal by using the IN switch to switch the OPTICAL COMPRESSOR
on and off.
GAIN REDUCTION (LED meter) - Displays the amount of gain `lost' due to
compression. Since compression reduces the volume of the signal, the meter drops as
compression is applied: for example, a 10 dB drop shows as -10 on the meter.
COMPRESSOR SIDE-CHAIN INSERT (rear panel connector)
This is a TRS jack connector, configured in the same way as the main channel
INSERT (tip = send, ring = return), which allows an external processor, such as EQ,
to be inserted into the side-chain of the compressor. This allows frequency conscious
compression techniques, such as de-essing, to be applied.
STEREO LINK (switch) - TwinTrak Pro can be stereo-linked, providing true
IN (switch) - Switches the OPTICAL COMPRESSOR into the signal path. stereo compression, allowing you to work with a stereo signal using just one set of
When engaged, the red LED in the switch cap is lit. controls. With STEREO LINK engaged (in), the top channel controls become master.
When in stereo mode, gain reduction is only displayed on the master channel meter.
COMPRESSION (knob) - Turning this knob clockwise increases the amount See WORKING WITH STEREO SIGNALS on page 10 for further information.
of compression by lowering the threshold. Turning the knob counter-clockwise
decreases the amount of compression by increasing the threshold. Thus, this knob is OUTPUT LEVEL
essentially an inverted threshold control. Note that the signal is only compressed when
it exceeds the threshold, so quieter passages maintain their natural dynamic range,
whilst loud passages (that exceed the threshold) are compressed.
6
ENGLISH
The controls in the LATENCY-FREE MONITORING section allow the engineer
or artist to construct a headphone/external monitor mix as follows:
INPUT BALANCE (knob) - Allows you to adjust, within the monitor path, the
stereo balance between the two input channels.
MONO (switch) sums together the two monitor input channels, sending a
mono signal to both left and right monitor outputs.
The inclusion of two custom peak-reading meters in the TwinTrak Pro's output FX RETURN (knob) - Allows you to balance, within the monitor path, the
section allows the user to accurately monitor the levels being sent to external analogue amount of effected versus dry signal. The dry internal signals can be blended with the
or digital equipment from the TwinTrak Pro's analogue and digital outputs. The peak- effected signal in the monitor mix by adjusting this knob, which runs from DRY (no
reading meter displays levels from 24 dBfs to 0 dBfs. An overload LED shows when effects) to WET (full effects).
levels are excessive - if this lights, reduce the level of signal being fed to the outputs
using the controls in the MID SCOOP EQ and COMPRESSOR section (this This is a better than adding plug-in effects with the DAW for two reasons; firstly it
assumes that your input LEVEL is already set correctly). eliminates any latency issues between input and playback signals, and secondly all the
adjustments are localised conveniently on the front panel rather than being spread
LATENCY FREE MONITORING throughout the recording system. See FX SEND AND RETURN in the following
section for further information on feeding FX units into the monitor path.
Note: The stereo FX SEND AND RETURN can also be used as a dual mono FX
send and return, allowing you to feed different effect units to each channel. However,
the FX return control is global, controlling the effects levels on both sides in equal
proportions.
HEADPHONE MIX (knob) - Allows you to control the balance between the
signals being tracked and the pre-recorded stereo mix fed to the monitor inputs from
the DAW.
The LATENCY FREE MONITORING section is used in conjunction with the
MONITOR LEVELS section to provide flexible monitoring of both the signal being MONITOR LEVELS
recorded and an existing stereo mix.
Latency can be a major problem when recording to a computer-based digital audio
workstation (DAW) via a sound card. If the signal being recorded has to pass through
the DAW before being monitored, significant delays may occur as a result of the digital
conversion and processing that takes place, making it difficult or impossible to sing,
speak or play in time with any pre-recorded tracks being played back.
The TwinTrak Pro's LATENCY-FREE MONITORING section allows the user to MONITORS (knob) - Allows independent control over the level being fed to
monitor a mix of both the mono or stereo signal being recorded (fed directly from the external monitors.
unit before it passes through the digital recording system) and a stereo mix of pre-
recorded tracks (acting as a mini mixer). Thus latency is eliminated and the recording HEADPHONES (knob) - Allows independent control of the overall level being
artist can speak, sing or play along to the pre-recorded tracks in perfect time. fed to the headphones.
7
ENGLISH
Adding FX at this point does not affect the dry signal that is being recorded, but allows
HEADPHONES TO MONITOR (switch) Allows the headphone mix (as reverb to be used to help an artist feel more comfortable when monitoring their own
determined by the HEADPHONE MIX knob) to be sent to the external monitors via performance.
the monitor level knob. This means you can set up a headphone mix and switch it to
your monitors whilst retaining independent control over the headphone mix level. DIGITAL
MONITOR MUTE (switch) - Mutes the output to the monitors (but not the
headphones).
These controls allow the balancing between dry/wet and signal/monitor to be adjusted
independently, making it quick and easy to set up. They also allow the artist to tweak
his or her own headphone mix without affecting what the engineer is recording.
LATENCY FREE MONITORING CONNECTIONS
MONITOR INPUTS - These inputs are provided on balanced (+4 dBu) TRS
jacks. They allow routing of your main stereo mix outputs (e.g. from DAW sound
card output) to the TwinTrak Pro's LATENCY-FREE MONITORING section. ADC LOCK (LED) - TwinTrak Pro features an ADC lock LED that illuminates
This means that you can monitor both the stereo mix already recorded, AND the when the optional ADC is synchronised to an external wordclock source. If an
processed signals from your TwinTrak Pro at the same time. You can leave your external wordclock source is connected, the ADC LOCK LED should light
TwinTrak Pro permanently rigged up in your recording system for tracking or re- continuously. If it flickers it indicates bad jitter on the synchronising signal, requiring
processing, whilst also allowing you to monitor the output from your main DAW. investigation of the wordclock-generating device.
MONITOR OUTPUTS - These outputs are provided on balanced (+4 dBu) DAC SIGNAL (LEDs) - TwinTrak Pro is the first Platinum unit to feature a
XLR connectors. They allow routing of the signal connected to the MONITOR DAC (Digital to Analogue Converter) as standard. This feature enables the user to feed
INPUTS (e.g. main stereo mix from DAW sound card output) to a pair of powered stereo or dual mono digital signals into TwinTrak Pro, either for the purpose of
monitor speakers or monitor amplifier inputs. Note that these monitor outputs are monitoring, or to be re-processed through TwinTrak Pro's MID SCOOP EQ and
separate from the headphone bus, and will relay only signal that is fed from the OPTICAL COMPRESSOR sections. Two LEDs (left and right) show whether signal
MONITOR INPUTS, unless the HEADPHONES TO MONITOR switch is (either mono or stereo) is flowing through the DAC. These LEDs illuminate when the
engaged (see LATENCY FREE MONITORING section above). signal flowing through the DAC exceeds -12 dBfs.
HEADPHONES (front panel) This output is a standard stereo TRS DAC INSERT (switch) When disengaged (out), the incoming digital signal is
headphone jack, controlled by the HEADPHONES level knob beside it. sent to the LATENCY FREE MONITORING section to act as the monitor input.
When engaged (in), the incoming digital signal is processed through the TwinTrak
HEADPHONES MIX These rear panel outputs are provided on balanced (+4 Pro's input channels via the LINE input. N.B. the routing of the DAC signal to both
dBu) TRS jacks. They allow the headphones mix to be routed to an external amplifier, the line input and monitor input is via the normalising of the LINE INPUT and
such as a headphone distribution amplifier. The signal is taken `pre' the front-panel MONITOR INPUT TRS jack connectors respectively therefore it is imperative
HEADPHONES level knob, thus retaining independent level control of headphones that these connectors are not occupied by jacks when using the DAC.
connected to the front panel HEADPHONES jack.
DIGITAL CONNECTIONS
FX SEND AND RETURN - The rear panel has four balanced (+4 dBu) TRS
jacks. The send is taken `post' the balance and mono controls, and the return comes DAC INPUT - The format for the digital input is S/PDIF and is on a single RCA
back in via the FX MIX control. This allows the two audio channels of the TwinTrak phono (coaxial) connector. Wordclock output is also provided on a BNC connector.
Pro to be routed to and from an external effects device such as a stereo reverb unit. See page 10 for further information on wordclock.
8
ENGLISH
To understand how to use the impedance selection creatively it may be useful to read
DIGITAL OUTPUT OPTION the following section on how the microphone output impedance and the mic pre-amp
input impedance interact.
In addition to the analogue outputs, a high quality 24 bit, 128x over-sampled digital
output may be fitted as an extra cost option, and can operate at sample frequencies of
44.1, 48, 88.2 or 96 kHz. All of the following functions are available on the rear panel VARIABLE IMPEDANCE: IN DEPTH EXPLANATION
when this option is fitted:
Dynamic moving coil and condenser microphones
S/PDIF OUTPUT - This 24 bit output is S/PDIF format on an RCA phono Almost all professional dynamic and condenser microphones are designed to have a
connector. If 16 bit resolution is required, the receiving device should dither the 24 bit relatively low nominal output impedance of between 150 and 300 when
signal to achieve 16 bit performance. measured at 1 kHz. Microphones are designed to have such low output impedance
because they are then less susceptible to noise pickup and they can drive long cables
SAMPLE FREQUENCY (switch) - Two switches give a choice of four without high frequency roll-off due to cable capacitance.
sample frequencies as marked on the rear panel. The left-hand switch selects between
44.1 kHz (switch in) and 48 kHz (switch out), and the right hand switch doubles the The side-effect of having such low output impedance is that the mic pre-amp input
selected frequency, providing for 88.2 and 96 kHz sample frequencies. impedance has a major effect on the output level of the microphone. Low pre-amp
impedance loads down the microphone output voltage, and emphasises any frequency-
EXT WORDCLOCK INPUT - If an external wordclock source is fed to the related variation in microphone output impedance. Matching the mic pre-amp
BNC connector, the TwinTrak Pro will attempt to synchronise to it. When the unit is resistance to the microphone output impedance (e.g. making a pre-amp input
correctly locked to the external wordclock source the ADC LOCK LED will be impedance 200 to match a 200 microphone) still reduces the microphone output
illuminated (see above). See Wordclock on page 10 for more details. and signal to noise ratio by 6 dB, which is undesirable.
Fitting the card To minimise microphone loading, and to maximise signal to noise ratio, pre-amps
See the separate digital option owner's manual for instructions on how to fit the ADC. have traditionally been designed to have an input impedance about ten times greater
than the average microphone, around 1.2 k to 2 k. (The original ISA 110 pre-amp
design followed this convention and has an input impedance of 1.4 k at 1 kHz.)
MIC PRE-AMP INPUT IMPEDANCE
Input impedance settings greater than 2 k tend to make the frequency-related
A major element of the sound of a mic pre is related to the interaction between the variations of microphone output less significant than at low impedance settings.
specific microphone being used and the type of mic pre-amp interface technology to Therefore high input impedance settings yield a microphone performance that is more
which it is connected. The main areas in which this interaction has an effect are the flat in the low and mid frequency areas and boosted in the high frequency area when
level and frequency response of the microphone, as follows: compared to low impedance settings.
LEVEL - Professional microphones tend to have low output impedances and so Ribbon microphones
more level can be achieved by selecting a higher impedance position. The impedance of a ribbon microphone is worthy of special mention, as this type of
microphone is affected enormously by pre-amp impedance. The ribbon impedance
FREQUENCY RESPONSE - Microphones with defined presence peaks and within this type of microphone is incredibly low, around 0.2 , and requires an output
tailored frequency responses can be further enhanced by choosing lower impedance transformer to convert the extremely low voltage it can generate into a signal capable
settings. Alternatively, choosing higher input impedance values will tend to emphasise of being amplified by a pre-amp. The ribbon microphone output transformer requires
the high frequency response of the microphone, allowing you to get improved a ratio of around 1:30 (primary: secondary) to increase the ribbon voltage to a useful
ambient information and high end clarity, even from average-performance level, and this transformer ratio also has the effect of increasing the output impedance
microphones. Various microphone/pre-amp impedance combinations can be tried to of the mic to around 200 at 1 kHz.
achieve the desired amount of colouration for the instrument or voice being recorded.
9
ENGLISH
This transformer impedance, however, is very dependent upon frequency - it can wordclock synchronisation, but equally important. Timecode enables recording and
almost double at some frequencies (known as the resonance point) and tends to roll off playback devices to run in sync with one another, and carries a regular series of
to very small values at low and high frequencies. Therefore, as with dynamic and absolute time values (hrs:mins:secs:frames). The two timing systems are quite
condenser microphones, the mic pre-amp input impedance has a massive effect on the independent.
signal levels and frequency response of the ribbon microphone output transformer, and
thus the `sound quality' of the microphone. It is recommended that a mic pre-amp Wordclock set-up when using ADC only
connected to a ribbon microphone should have an input impedance of at least 5 times If no wordclock cable is connected, the TwinTrak Pro is the wordclock master, and
the nominal microphone impedance. the ADC transmits embedded wordclock via the S/PDIF connection. If a wordclock
cable IS connected to the ADC, the ADC can be slaved to an external wordclock
source.
IMPEDANCE SETTING QUICK GUIDE
Wordclock set-up when using DAC only
In general the following selections will yield the following results: For standard use, no wordclock cable is required, since S/PDIF carries the embedded
wordclock signal. If wordclock connection IS required (e.g. the user wishes to use a
High mic pre-amp impedance settings second low cost A/D converter which has only basic wordclock spec.) a wordclock
· Will generate more overall level cable can be connected to the DAC wordclock output to send wordclock signal to a
· Will tend to make the low- and mid-frequency response of the microphone flatter second unit's wordclock input.
· Will improve the high-frequency response of the microphone.
Wordclock set-up when using both ADC and DAC at the same time
Low pre-amp impedance settings Link the wordclock DAC output to the ADC's wordclock input using a short
· Will reduce the microphone output level wordclock cable. The DAC wordclock output regenerates wordclock at the point of
· Will tend to emphasise the low- and mid-frequency presence peaks and resonant exit. So, you can run embedded-in-S/PDIF wordclock into the DAC, then send
points of the microphone. wordclock out of the DAC wordclock output, which is then received at the ADC
wordclock input. You could also run the two separately, but this is the method we
recommend as the noise performance is theoretically the best (everything runs from a
WORDCLOCK single clock).
Whenever multiple digital audio devices are connected together digitally, all the
devices must be wordclock synchronised to avoid data transfer problems. All devices WORKING WITH STEREO SIGNALS
must send and receive their data at the same sample rate (e.g. 44.1 kHz) but they must
also have their internal clocks running in sync. This ensures that all units send, receive There are two basic techniques which can be used to record a sound source in stereo
and process their data streams simultaneously. Failure to achieve this will mean a drastic using two microphones. The first is to use a coincident pair of microphones. This
reduction in audio quality, and other unwanted audible artefacts, such as pops and technique uses a pair of identical directional microphones mounted as close to each
clicks, may occur. At a sample rate of 44.1 kHz for example, there are 44,100 spaces other as possible (typically one above the other) at an angle of up to 90 degrees from
every second that need to have samples inserted. If there is a slight drift in one of the one another, with each microphone feeding one channel. The microphones capture
clocks, some of those samples will be `missed'/will move forward one place, which level differences between the left and right sides of the sound stage because
results in distortion. directional mics are used, the level varies in direct relation to the physical angle
between the microphones and the sound sources.
To avoid such problems, every digital system needs to employ wordclock. One unit
should be designated the `wordclock master', and all others should be designated The second technique is to use two identical omnidirectional microphones spaced a
`wordclock slaves'. Setting this up is often simple, since most digital transfer formats fixed distance apart. These microphones capture sounds from different positions in the
include embedded wordclock data (e.g. S/PDIF, AES/EBU, ADAT). Where this is sound stage at slightly differing times because of the physical distance between the two
not the case (e.g. TDIF), wordclock can be provided via a separate wordclock mics, and so they record what is known as `time-of-arrival' information in the two
connection. Note that timecode synchronisation (e.g. SMPTE) is different to channels.
10
ENGLISH
The polar pattern of the directional microphones being used will affect the perspective
For a complex sound source, such as an orchestra, it may be necessary for the engineer of the recording, and therefore the positioning needs to be considered accordingly. In
to use a combination of one of the above techniques with some `spot' mics to bring this example crossed cardioids would probably need to be placed above the conductor's
distant sounds `closer' in the recording. head to pick up a full stereo image; a crossed figure-of-eight pair would have to be
placed further back in order to cover the whole orchestra. As a result of this
Coincident microphones positioning, cardioids will pick up less of the room ambience and give a much `closer'
sound whilst the figure-of-eights would produce a more `distant' sound and pick up
The coincident pair technique is the most commonly-used stereo microphone more of the room ambience.
technique used in radio, TV and commercial stereo recordings due to the fact that
this technique generally recreates the most faithful stereo image. Spaced omnidirectional microphones
Coincident microphones do not record `time-of-arrival' differences because the two Omnidirectional mics cannot be used in coincident pairs because their directional
microphones are mounted in such close proximity to one another that sound reaches response means they do not record level differences proportional to the angle of the
both simultaneously. The diagram below shows how an orchestra might be recorded incident sound. As a result, the only way to use two omnis is to space them apart and
using this technique, where the microphones marked `A' are in a coincident pair record the time-of-arrival differences. Spaced microphone techniques often do not
formation. create as accurate a stereo image as coincident techniques. This is mainly due to the
fact that when these recordings are replayed, there is second set of time-of-arrival
In this situation the two directional microphones are mounted on a stereo bar and face differences caused by the distance between the listener and the left and right
outwards so that the angle between them is 90 degrees. Using a stereo bar means that loudspeakers. This often has the result that the stereo image becomes `blurred', and can
the mics aren't in exactly the same horizontal position, but they are close enough for cause sounds to be perceived as grouped around the loudspeakers rather than spread
any time-of-arrival differences to be inaudible. The microphone pointing to the left of uniformly between the speakers to create a full stereo image.
the orchestra (at the first violins) would be panned hard left and the microphone
pointing to the right (at the cellos) would be panned hard right. So, why might you choose to use a spaced microphone technique over a coincident
pair? The main reason engineers choose this technique is so they can use high quality
omni-directional microphones, whose low frequency performance is generally superior
to that of directional microphones. It should also be noted that the quality of the stereo
image captured by a carefully set up spaced omni technique is not a problem in many
situations. The sound is still perceived as having width and the recordings often sound
more spacious than those made using coincident techniques.
The microphones marked B in the diagram above are spaced omnidirectional mics.
The mic to the left of the orchestra should be panned fully left and the mic on the
right should be panned fully right. The distance they are set apart depends on the
sound source being recorded but should generally be between a third and half the
width of the sound stage. How far the microphones are placed from the orchestra
would depend on the acoustics of the room and how much perspective was desired by
the engineer.
There are no hard and fast rules as to which is the best microphone technique for
stereo recording, and both techniques are capable of producing excellent results.
Whichever technique you choose for a particular situation, experimentation and
careful microphone placement are the keys to a successful stereo recording.
11
ENGLISH
A BEGINNER'S GUIDE TO COMPRESSION Let's take an example with some real numbers. If the threshold is set to -10 dB and the
ratio is set to 4:1, a