Empirical Labs EL-Rx - Manual (Page 5)

and turns the input into a balanced amplifier, allowing the DocDerr to handle very hot signals without
clipping, and the module becomes a great mix or line level tracking processor.
3 Pin Jumper Settings
Above is a diagram pointing out the 3 user selectable jumpers, affecting audio and compressor
detector. All jumpers are shipped in the left (front) position, which is factory default.
INPUT GAIN JUMPER - For direct instrument inputs, such as an acoustic guitar, one would set the
INPUT GAIN Jumper to the right (NOT as shown). This provides 16 dB of single ended gain when
input pin 3 is shorted to ground, as a normal guitar cable would do. This gain is usually enough to
bring up electric instruments to line level, while still providing a margin of safety for certain active
instruments. It will help the MIX control also, making the dry level closer to the compressed level, so
sweeping between them won’t be so radical. For line level signals, keep jumper to the left (front).
DETECTOR HP JUMPER - This jumper allows the user to optionally roll off low frequencies going to
the detector of the compressor. When in the right (rear) position, this filtering keeps the compressor
from responding as much to the low frequencies, which often have great power, therefore sometimes
getting over-compressed, subjectively speaking. However, since the compressor is so versatile, it’s
usually preferable to tame the subs as well, by sending a full bandwidth (FBW) signal to the
compressors detector (jumper to the left as shown).
DIFFERENTIAL OUT JUMPER – Changes output configuration. This jumper sets the XLR output
pin 3 to either balanced ground, or the inverted phase of what’s on pin 2 of the output XLR. It is set
to the left, differential mode, from the factory, adding 6 dB more gain. Setting the jumper to the right
(towards the rear) disconnects the amplifier on pin 3, decreasing the output gain by 6dB.
Multi-Button Controls: Lastly, to get started you should learn three special button combinations.
Pressing two buttons at once will cycle through the following parameters:
HP Frequency - Press LF and MF to change HP Frequency from Off, 70Hz, and 100Hz.
Mid PEQ BW - Press MF and HF to change Mid band Q (bandwidth). LED indicates narrow Q.
Disable Compressor - Press LF and HF to disable/enable compressor.
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Disabling the compression can be done with software by pushing the LF and HF buttons
simultaneously, allowing the DocDerr to behave almost as a tape-like saturation/distortion box.
A Det HP jumper on the PCB can make the compressor respond less to low sub frequencies.
The DocDerr is shipped in FBW (full bandwidth) mode, with the jumper towards the front, which is
usually preferable, especially bass instruments. Moving the DET HP jumper to the rear position rolls
off below 150Hz to the compressor detector, and can help prevent LF pumping for midrange sources
like vocals and acoustic instruments. It is sometimes useful for buss compression as well. The HP
EQ filter often prevents pumping also, as it filters out subs in the audio path before the compressor
sees them. See P3.
The Saturator
The saturation circuit follows the compressor, and tends to catch high frequency peaks that get
through, softly flattening them out. It was largely tailored to simulate the characteristics of tape
saturation. Germanium semiconductors are used to more smoothly round the peaks to produce
lower order harmonics. We use special filter circuits to shape how different frequencies are soft
clipped. This saturator circuit is always in the path of the compressor signal. When the mix control
is set to 0 (dry), the saturator and compressor are both out of the path and do not affect the output
signal. The saturator will add lots of harmonics to low frequencies, and soften high frequencies.
As mentioned above, pressing the LF and HF buttons will toggle the compressor off and on,
allowing you to use just the germanium saturation circuit with no compression. Very tape-like!
The Mix Control
This is a clean mixing circuit that allows the user to blend the EQ’d uncompressed signal with the
EQ’d, compressed and saturated signal, and has incredible phase alignment through 20KHz. This
simple circuit gives the user incredible flexibility in how the compressor/saturator is used. As already
mentioned, the user can sometimes put lots of compression on a signal, and mix it back under the
dry signal and get a natural full sound, with dynamics, and lots of sustain. There will be a slight level
drop in the middle of the Mix knob range, partially because the compressed signal sustains notes
tremendously, but the uncompressed peaks are attenuated. Once you back down from 10 on the
Mix, the loud sustained level will drop quickly, but you may have a very nice natural dynamic sound.
Conversely, you will also notice a quick change in the loudness and sustain, when you nudge the
mix control above 0. The mix control is heavily dependant on the input signal’s level. There are lots
of marks on the Mix control to aid in recalling settings, especially between 8 - 10.
Wiring the DocDerr
There are two main ways to setup and wire the input of a rack with the DocDerr module installed.
1) “Instrument In” with a single ended input (usually a mono standard guitar cable) and 16dB of
gain,
2) “Line In” which is lower gain and can be differential.
There is an INPUT GAIN jumper located in the middle rear of the board that can be switched
between two positions, Instrument In (Inst) and Line In. This jumper changes the mode which the
input amplifier works, changing it from a high impedance amplifier with gain, to a lower impedance
differential input amplifier with no gain. So before installing your module, set this jumper to the
proper position.
Most API 500 compatible racks do NOT have a 1/4” guitar jack input, so we supply a female
1/4” jack adapter that goes to male XLR. Plugging a standard guitar cable into this adapter will work
perfectly for “Instrument In” mode. The guitar cable will short the sleeve to ring, shorting the ring (pin
3 on the XLR) to ground. When the Input Gain jumper is set to the rear in “INSTRUMENT IN” mode,
this will result in a very clean 16dB of high impedance gain.
As shipped from factory, the output is balanced differential, and 6dB louder than the alternate
single ended output setting. The single ended mode, with the jumper to the rear, has balanced
impedance, which can prevent any output wiring problems (See P3). For recording you will usually
use the balanced differential mode as it has 6dB more gain and will hit the recorder with a better
signal. If too loud, use single ended mode. When using the differential out mode, don’t short any of
the Active XLR output pins (usually Pin 3) to ground. Let the unused pin 3 “float” (stay
unconnected). Separate amplifier drives each of these pins, so grounding one of them will short the
associated amplifier out. So in the Dif Out mode, if you only use pin 2 on your output cable, leave
pin 3 unconnected. When going to a single ended patch bay or other device, using the single ended
jumper setting (jumper towards rear) will work just fine, and take some guesswork out of wiring.
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Det HP Differential Out
DI
PreOut
16dB
FBW
Dif
50V
U1
U3 4
U9 8 U7 5
11 U12 13 U14
29
27 28
U19 18 U17 16
25
U2
S
/N
________
DocDerr R3
Empirical Labs
5/20 2011 c
Input Gain
Line Inst +16 FBW 150Hz HP Dif out Single Ended
Section Details (cont’d)
There are three bands of parametric EQ, whose frequencies are selected by the three
switches. The seven frequencies for each band are labeled above and below the LEDs. When two
LEDs are on in the frequency select section, the frequency is notated below and between those two
LEDs. This allows us to indicate 7 frequencies with 4 LEDs. This PEQ’s (Parametric EQ)
performance is very high and based on Empirical Labs Lil FrEQ circuitry.
The plot above shows the actual curve shapes of the three parametric EQ sections at full
boost & cut. Each band is capable of 14dB of boost and cut, making the full range of the boost cut
knobs quite useful. The mid band has its two Q (bandwidth) shapes shown, centered here on 2KHz.
The most touchy place on the knobs is at the extremes, where the marks on the front panel get close
together. Marks on knobs are 1dB apart. Notice the frequency response of the EQ section goes
beyond 200KHz, something that digital processors cannot do.
The Mid band has the widest default Bandwidth (BW) but is switchable to a narrower band for
cutting problem spots or feedback. The Q of this band is switched by pressing the MF and HF
switches at the same time. With each dual button press, the Q will cycle back and forth between
wide and narrow. This is also noted on the front panel, and indicated by an LED with a narrow Q
graphic above it. See plot above. Great EQ section for great big wide ol’ scoops (cuts).
The frequency selection was originally tailored for acoustic instruments, especially acoustic
guitar. Often internal acoustic instrument pickups will have midrange resonances that need to be
tamed by generous cuts at the problem frequencies. Therefore, we offer the greatest frequency
selection in the midrange area.
The Compressor
The INPUT KNOB is the compressor’s main control (not counting the MIX control), which
affects how much compression, is put on a source. The INPUT Knob follows the EQ, and drives
signal into the compressor, scrunching the dynamics and peaks into an increasingly narrow range.
The time constants and the curve of the compressor were selected to be as aggressive as possible
without crackly unmusical distortion. The ratio is about 5:1 but has a huge 5dB knee. With an attack
under 1mS, it could be considered a “limiter”. It has been compared to an LN1176.
Above about 8 – 10dB of compression there will be saturation caused by fast time constants
working on each peak of the waveform. We think it sounds very “tubey”, with nice harmonics added
at high gain reduction… but, it IS a form of distortion, and it will get more prevalent with more gain
reduction. Many of the classic old compressors from the 60’s and 70’s were valued for this fat
distortion. One can tame any saturation by turning down the input knob, thereby turning down the
compression, OR, by adjusting the MIX control to include more of the uncompressed (dry) signal in
the output. When using the MIX control, the user may find they can put on tons of compression (up
to 20dB), and still get a very natural sounding instrument or voice. By judiciously mixing the
compressed signal under the dry signal, the sustain and note detail will come out without feeling
squashed. Modern mixdown engineers use this “blend” technique all the time, but have to split the
signal going to a compressor and then return it to submix the dry and compressed signal on their
mixing console. For the first time, the common live instrumentalist can use this advanced
compression technique just by turning a knob.
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Example Settings
The DocDerr provides a new level of processing power in a single API 500 module. Originally
the main target user was the live performer who traditionally has a thin, out-of-control sound from
his/her guitar or other acoustic instrument. But like most Empirical Labs products, the versatility of
the DocDerr makes it useful on practically any source. Also, because of the no-compromise build
quality of the DocDerr, it is an excellent studio processor/preamp as well. We will start our example
settings on Acoustic guitar, especially those with built in pickups.
Acoustic Guitar & Plucked Instruments
– Acoustic instruments are extremely
sensitive to tone alteration. Mic selection and placement, along with a good instrument is your first
resource during performing or tracking. It’s always best to try getting the source to sound right
WITHOUT Processing. A good player should also be sensitive to the sound he gets off the
instrument, and adjust how and where he hits the strings. However, we have stuffed enough
processing into this little module that combined with the eq on the instrument, you should be able to
get a first class sound, even with an instrument that has poor basic tone. If you are tracking
(recording the source for the first time), the user will find endless ways to alter the tone with the
DocDerr. The output level can be adjusted up or down 6dB for recording with the output jumper.
Lets look at acoustic instruments with built in pickups, since they are the most common for live
performances. Internal pickups are very non-ideal transducers. First they are usually partially, or
completely inside the instruments, some place your ear never is. They pick up hardly any “wood” of
an acoustic instrument. Secondly, the transducers have a frequency response all over the place, and
the best a designer can hope for is a transducer’s frequency response to compliment the
instruments. Often the guitar designer will provide basic EQ for the built in transducer to help
improve the basic tone. The DocDerr’s built in EQ will enable the user to work on frequencies in a
way not possible with the built in instruments tone controls. Combining both the instrument’s
onboard eq with the DocDerr’s 4 section EQ gives the instrumentalist great tone shaping power.
The EQ selection and the compressor was tailored for “electrified” acoustic instruments. The
most common problems are midrange frequencies that pop out during different types of playing, and
over dynamic instruments without sustain. The compressor fixes the over-dynamics and lack of
sustain and “size”, while the EQ can do wonders for the basic tone.
The player & engineer will find that often what works for a solo instrument can be disastrous on
an instrument in the mix with other instruments. Low frequency Boominess, a common problem, can
be fixed with a gentle bass roll off using the Low PEQ, or with the steeper high pass sections. Again,
while mixing, its best to EQ the instrument “in the mix” to make it fit tonally. While soloing, there is
often a tendency to thicken it up, which will translate to muddiness when combined with the bass and
other instruments. The high pass filter is EXTREMELY useful to open up frequencies below 120Hz
for other instruments. The 70Hz filter will leave all the fundamental frequencies of an acoustic guitar
intact, but get rid of thumps and low frequency body rumbling. It is especially useful for the solo
guitarist who wants a BIG sound, without rumble. The 100Hz filter is still out of the way of most
fundamentals, but cuts down on the size of the guitar sound, making it useful in ensemble playing.
On records, when an acoustic is part of a band, engineers will often cut higher frequencies up
around 120 – 150, preventing “muddy” sounding mixes. One can use the LF parametric section
alone, or combined with the HP to achieve this with the DocDerr.
The tone and body of an acoustic guitar is in the 160 to 500Hz range. Too much in this range
and the instrument sounds dark and “wooly”, while too little can make it thin. Sometimes it’s
necessary to boost AND cut at close frequencies down here. Get used to the drop in level when you
cut frequencies in this range. Sometimes cutting one mid frequency generously can fix a whole
guitar tone, yet its easy to get fooled when A/Bing it with the orignal. Eq’ing with the compressor can
prevent the misleading level drop. One can use the midrange with narrow Q (press MF and HF
buttons to narrow this Q or bandwidth), to surgically pull 500Hz or higher frequencies out. 400 –
1KHz is often a good point to cut frequencies to brighten and fill the lows and highs. It is above most
fundamental frequencies, but below the frequencies that help the instrument cut thru in a mix.
Many guitars have honky midrange in the 1 – 8KHz range, especially when the player is playing
hard (loud). Try pulling 6dB at 1-4KHz with the midrange EQ, wide bandwidth, and see if that makes
the guitar rounder. If this sounds dull, try moving the frequency lower (1KHz?), or perhaps you need
to pull a couple different points at say 1Khz and 4-8Khz. Sometimes pulling as high as 10Khz will
smooth the tone without dulling. The upper midrange on acoustic instruments changes drastically
depending on how the instrument is played, and even if the guitar part uses open strings, or finger
fretted strings. Eq’ing an acoustic instrument with a pickup is a series of compromises. Don’t forget
to use the tone controls on the instrument itself, for more eq power.
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