The audio modes, Distortion generator, Troubleshooting – Empirical Labs EL-8 User Manual
Page 11: Upgrades, The ratios and their curves, Classic emulation, It’s not only a compressor but a, The distortion modes, Fuse, Line voltage select
The Audio Modes
To switch between the "Audio" modes, press the button labeled Audio. The LED's above the switch will
cycle through 6 states. In order of occurrence:
1) Norm - (No LED's lit) Low distortion and full frequency range.
2) HP - High-pass (Green LED) Smoothly cuts low "mud" audio frequencies.
3) Dist 2 - (Yellow LED) Emphasized 2nd harmonic distortion.
4) Dist 2 & HP - Combination of 2 and 3 above.
5) Dist 3 - (Red LED) 3rd harmonic emphasized.
6) Dist 3 & HP - Combination of 2 and 5 above.
The High-pass mode (HP)
The first mode cycled to after normal is HP (or High-pass). With the HP LED on, the unit rolls off low
"sub" frequencies below 80 Hz in the audio. It is a very smooth Bessel filter, about 3 dB down at 65Hz
and -12 @ 30Hz. Its final slope is 18 dB per octave but is below all but the very exceptionally low vocal
tones. Rolling "subs" off of a singers mic is an excellent use for this filter. This can also be selected
along with either Dist 2 or Dist 3 modes as explained below.
It’s not only a compressor but a ...
"Distortion Generator"
The Distressor is a modern digitally controlled analog device that attempts to offer some of the "musical
non-linearities" exhibited by the older tube, class A discrete, and magnetic tape mediums. The old,
sought after vintage gear is not anywhere near as accurate (or linear) as devices made today, but
certain "faults" or non-linearities are exactly the reason some sell today at 10 times their original value.
They color the sound with distortion and frequency response shaping. Getting the frequency response
flat to 20kHz and having distortion below .5% used to be an achievement. Today, a 35 cent op amp is
flat to 3 MHz and produces distortion below .002%. Getting things accurate in the digital age is
relatively cheap and easy. But getting the expert user to think a piece of gear is "musical" and fun to
use is something else.
The Distortion Modes
By using a design that allows pinpoint control of nonlinear analog devices, the Distressor is trimmed to
produce three controllable distortion modes:
1. Normal (Clean) No induced distortion. THD hovering between .025 and .3%
2. Dist 2
THD hovering between .05 and 3% Emphasized 2nd Harmonic
3. Dist 3
THD hovering between .1% and 20% 3rd Harmonic increased.
Dist 2 Mode
It is well known that the triode distortion in tube circuits produces lots of 2nd and 3rd harmonics, in
somewhat varying ratios. These lower order harmonics form "the octave" and "the octave and a fifth"
to the fundamental musical tones. They are actually "musical" distortion. Harmonics well above the
2nd and 3rd are usually considered more harsh and unmusical, and therefore should be lower in
amplitude (<-60 dB) to keep with our line of thinking. Second harmonic is considered to be the
warmest and most "consonant" harmonic distortion and is usually very hard to hear, especially on
single tracks. The Dist 2 mode on the Distressor emphasizes the 2nd harmonic (octave), especially
while compressing.
Dist 3 mode & the Distortion indicators
This mode emphasizes the third harmonic. This is basically caused by nonlinear gain that results with
the top and the bottom of waveforms being flattened out. Analog tape saturates in this manner. The
3rd harmonic is induced in the Distressor by increasing VCA output level. We have provided distortion
indicator lights that come on most frequently in Dist 3 mode. A yellow LED light indicates .25% THD
and the red "redline" LED indicates 3% THD or more. Though not always an exact indication of the
distortion, these LED's are an excellent guide to where the user is in the "Grunge Department" and can
help to avoid turning the music into an "overwell" mess. You will find that the harmonic distortion is
generally more obvious on overall mixes and complex programs. On individual instruments,
sometimes 3% distortion sounds "fat" and "analog" and isn't heard as distortion at all.
5
Troubleshooting
* No sign of life - Check power cord for firm connection. If still no life open top cover by removing all
top screws and check fuse toward rear next to transformer. If it is blown, pry it out and replace it with
extra fuse provided in fuse holder toward front of chassis. If fuse is OK, make sure your Voltage select
switch is set to current wall outlet voltage (115, 230 VAC).
* Unit keeps blowing fuses - Probably has short or power supply problem. Try to make sure there is
nothing trapped under the PC board, shorting to the metal case. Attentive visual inspection is still the
most effective troubleshooting tool available. Check internal voltage select switch for proper settings
(115/230).
* Unit is on but not doing anything - The unit may be bypassed or in 1:1 mode. If bypassed, you
need to press the "BY-PASS" button so red LED goes off. The 1:1 mode may be inaudible but the
input and output levels will still affect it. Try another ratio for compression.
* Bargraph shows gain reduction but very little or none is actually occurring -The unit is probably
severely out of adjustment. We use very stable trim pots and high quality components, but it is
possible that long term component aging or failure may require factory re-calibration. Right now you will
have to return the Distressor to factory for re-calibration. In the future there will be local dealers and/or
service centers to help.
* Distorted output - If there is severe, un-musical distortion, chances are you're hard clipping. Check
that the output cable is properly wired and any unused output pins (2 or 3) on XLR are floating (left
unconnected). Shorting an output pin will not harm the unit but can show up as distortion in the output
driver. The distortion this unit is meant to impart is harmonic and should not sound like crackly
distortion caused by hard clipping. Long attack times can clip transients in lower ratios when Dist 2 or
3 are employed. If the attacks are too fast (towards 0), low frequency clipping and unpleasant
distortion can occur. Try slowing up the attack or release.
* No output level - Make sure there is audio getting to unit, and that the input and output levels are
turned up.
* Unit pops or unnaturally pumps with low frequencies at ultra fast attacks when compressing 20 dB
or more - Possibly caused by the high-pass (HP) in the detector engaged, and not controlling the low
frequency amplitude in the VCA, causing offset pumping. Turning up attack (to 5 or above) will often
eliminate the effect. Remember that this unit has an extremely fast attack time that can show up as
pumping or crackling on low frequency laden material. You can control this with a slower attack, or a
slower decay. Also, try enabling and disabling the "HP" in the detector.
* Unit seems noisy - The dynamic range of the Distressor is greater than CD (16 bit) quality. However,
if you are compressing a noisy signal, the noise is pushed up along with the soft signals. If you have
20 dB of gain reduction on a room mic that has a 90 dB S/N, the noise floor will be raised 20 dB in
quiet areas, bringing the noise floor up to 70 dB. Since the Distressor is capable of lots of compression
without sounding unnatural, you can often bring noise or hiss up undesirably. Remember your current
input level, and then ensure that the noise is coming from outside the unit by turning the input knob off
(to 0). All noise should disappear. Try gating before compressing.
* Unit forgets where it was when power was shut off - Non-Volatile cap backup may have become
defective. Please call factory for information on replacement.
* Unit quits working when Bypassed – Pins 2 & 3 may be reversed on one of the XLR cables.
* Unit only works in Bypass – Input or Output are turned to 0, or input and output wiring is reversed.
* The Stereo Link in the Detector doesn’t seem to have an affect. User may have a radically
different source in the left and right channels. Consider installing the Stereo Image Link (see p13).
A note on Bypass and the Multiplexed Controls
A hardwired bypass relay enables the user to compare processed and unprocessed signals accurately.
When comparing the original signal from the processed signal, matching the output level with bypassed
signal makes it very easy to hear the processing changes. Bypassing can cause audio “clicking”.
To change ratio, audio, and detector modes, press the associated button and cycle through the
options. These step function controls are sometimes inconvenient when trying to compare two
settings, but if there was a control switch for every selection offered on the Distressor, there would be
15 switches on the front panel instead of four. We considered it very important to fit it all in the single
height 1.75" cabinet - and 15 switches just won't go. The color encoded, indicator LED's were arranged
in an easy to read pattern, with Red LEDs usually indicating radical or distorted settings.
10
Fuses, Operating Voltage & Non-Volatile
Memory
Caution: Always unplug unit before removing cover!
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11
The Ratios and their Curves
Each "ratio mode" of the Distressor sets both the threshold and the ratio, in the standard sense of the
word. This was done to provide an easy to set, yet versatile group of curves. The 1:1 mode provides no
compression, but allows the audio to pass through the "warming" circuits of the unit (we'll get to the
distortion modes in a moment). Ratio's 2 through 6 are general purpose curves great for tracking. The
2:1 and 3:1 ratios are "parabolic" knees - very gentle curves that won't typically go into hard limiting and
therefore, also won't provide absolute overload protection. Ratios 4:1 and 6:1 have steeper knees and
are good general purpose curves that gradually move towards hard limiting, "nailing" the signal in its
place. The ratio of 6:1 is very useful for vocals, bass, and acoustic instruments. It has an easy slope at
first until after the knee, where an increasing ratio "musically" limits the peaks of the signal before
damage is done. The 6:1 and 10:1 Opto ratios employ shorter knee limiting, reminiscent of some old
classics from the 60's and 70's (see Classic Emulation).
"Nuke" is a different story. The "Nuke" ratio was developed for room mics, but we have since found it
useful in many areas. "Nuke" has a medium threshold but when the signal hits it, a nuclear blast won't
budge the output level. It is brick wall limiting, keeping any normal signal within 1 dB or so. Just patch
in a room mic while recording drums (or other instruments) and slam the meters. Try attack on 4 and
release on 2. The release curve of "Nuke" is logarithmic, meaning it lets off quickly at first and then
slows. This release curve is a big part of the Distressor's sound. Experiment with the release times -
this guy can release really fast without too much crackling, even on bass. 20:1 can be used similarly to
"Nuke". Each of these curves again has their own feel to them, with the release slopes slightly altered,
and the knees falling in slightly different places. Most exceptional are the 2:1, 10:1 and Nuke ratios,
which employ special detector circuitry.
Just what is a soft knee?
A "soft knee" is a compression curve where the first few dB of gain reduction occur at very low ratios,
gradually increasing as the signal increases (gets louder). This makes the onset of compression very
hard to detect. The knee usually extends for a few dB and gradually flattens out toward a final ratio. All
curves with the exception of 20:1 and "Nuke" have dominant knees. The 2:1 ratio has a knee that can
be as long as 30 dB, depending on attack and decay settings.
Classic Emulation
Since the unit is based on the oldest compressor topology, the unit can be made to sound very similar
to older classics. The nonlinear nature of the older gain control elements of opto-couplers, FET's,
pentode (or triode) tube bias or "mu" modulation, etc., can be closely emulated if proper settings are
used. A special "Opto" mode has been provided in the 10:1 ratio.
Some Examples:
* To simulate the opto-VCA models of old (the LA-2A, LA-3A, LA-4A), try 10:1 "Opto" ratio, with attack
on 10, release on 0, Det HP on. Adjust input and outputs to your taste. Keep the attack above 4 to
keep the OPTO flavor. Faster attacks will give you a more aggressive sound. Remember our LED
metering deflects much faster than the old VU's so don't be afraid to hit the unit quite hard (10-20 dB of
compression on peaks). To emulate tubes, try Dist 2 & 3 mode, but let your ears be your guide.
* For a classic “Over E-Z” type sound, try ratios 2:1 thru 6:1, att 9, release 2, clean mode.
* 1176LN 6:1, Att 0 - 3.5, rel 1 - 10.5. Use ratios 3:1, 4:1, 6:1, 20:1 to emulate 4 1176LN ratios. Clean
mode is appropriate (Dist 2 or 3 off). Remember that the 1176LN attacks extremely fast and you must
keep attack under 4 max. A familiar sound is 6:1, att2, rel 4.
* Old Fairchild IGFET - 6:1 att 3-5, rel 2 - 7 (start with att 4 and rel 4)
Due to the transformerless design, you will maintain a low transient intermodulation distortion, but will
get the warming grunge of 2nd and 3rd harmonic distortion, if distortion modes are enabled. Also,
unlike some of the older units, the Distressor is uniform and predictable from one unit to the next.
Precise factory calibration assures that if you go from one Distressor to another, these settings will all
sound the same.
Empirical Labs would like to thank Universal Audio for not only creating classic audio gear, but for
kindly allowing us to refer to their model numbers. As they say “Once a classic, always a classic.”
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