the world of vacuum tubes, nothing is new. It should be no surprise
then, that "Tube" Limiters have existed since the early
days of radio, becoming popular in recording studios through
the fifties and early sixties. Altec, Fairchild and Universal
Audio were building tube limiters then; Manley and Tube-Tech
make all-tube versions now. What differentiates the Pendulum
6386 from the rest is its hybrid design. The front-end consists
of an input transformer followed by a 6386 tube (the same dual-triode
that was used in the Fairchild). The rest of the circuitry consists
of high performance opamps, biased for Class-A operation to lower
the distortion below that of standard Class-AB. All connectors
and tube sockets are gold-plated. Layout is clean and straightforward,
with special attention to internal grounding so that external
interference won't be a problem.
in previous articles, Fairchild built disc-cutting systems and
their stereo limiters interfaced directly with their cutting
amplifiers - hence the "Lateral" and "Vertical"
control designations. Unlike our "modern" 45/45 system,
Fairchild created a matrix, combining left and right into mono
(the lateral signal) and subtracting left from right to make
the vertical groove component. To do this required many transformers.
Pendulum's designer, Greg Gualtieri, wanted the functionality
of the Fairchild without all of the 'iron' clouding the signal.
JUST MY LUCK
to be very heavy handed when reviewing compressor / limiters.
After cranking up the 6386 and getting those meters swingin'
wildly, I found that it remained clean, open and airy as expected,
despite the abusive settings. However, I felt I hadn't crossed
the threshold into where it really began to have a "sound"
Well, in fact, I had passed it.
the beauties of reviewing products made by small companies is
the ability to communicate directly with the designer. therefore,
after my initial tests, I picked up the phone and called Mister
G. our chat resulted in a personal sonic revelation.
that the slow response of a VU meter inhibits its ability to
register transients (drums, percussion) while more accurate needle
movement occurs with average material such as vocals, bass and
crunchy guitars. Despite the geek degree, I did not transfer
this knowledge of VU meter characteristics to its inability to
display transient amounts of gain reduction, Until now...
not record a tambourine at 0 VU on an analog tape machine because
the transients are 10-dB to 15-dB higher. I got the sound I was
looking for with the 6386 set to FAST mode, with no control options
except Threshold and no more than 1 dB of meter movement when
viewing the amount gain reduction. In Fast mode, the 6386 is
doing much more than the 1-dB of meter movement indicates. Much
has a three position Mode switch, labeled Fast, Presets and Manual.
There is no Ratio control and the 6386 vacuum tube doesn't need
a dominatrix to get it to move. The way it reacts to the FAST
preset is impressive. It simultaneously turned on the mental
light bulb while humbling me with its almost hidden power. The
first four presets are modeled after the Fairchild, while the
last two presets -one faster than the other - are both program-dependent
to minimize "breathing."
IN MY ROOM
the 6386 and Pendulum's OCL-2 (optical tube compressor) and installed
them in a rack along with a Great River transformer-less mic
preamp and the TASCAM DA-45HR 24-bit DAT recorder. The rig was
schlepped to a room to make a stereo recording of a rock band
in rehearsal mode. I set the band up around a pair of spaced
omni mics (AKG C300 bodies with CK92 omni capsules).
another room I listened through Fostex headphones while experimenting
with both limiters, using one, then the other, sometimes both
and sometimes none (taking detailed notes). Up until this point,
I only used the slowest Attack and fastest Release settings to
play it safe. More aggressive tweaks were planned after the recording.
the ranch I listened on two systems, one not so great, to prove
the original purpose of compression - to squeeze a wide dynamic
range into a smaller dynamic space. As deranged as some boom
boxes can be, most only have between 5 and 10 watts of power.
A single guitar amp has way more than that, not to mention the
bass amp and the drum kit.
on the compromised system - computer speakers with a subwoofer
- I began with the slowest Attack and fastest Release settings,
which in this case are 40mS and 0.1S, respectively. Attack time
was gradually increased until the small amplifiers stopped distorting,
taking maximum advantage of their limited dynamic range and making
a DAT copy for later comparison.
On my real
system, which features Dynaudio BM15A self-powered monitors,
I quickly realized that reducing the dynamic range only confirmed
what my ears (in the original recording space) had first told
me - that the band's playing was a bit too sloppy and no magic
box was going to polish their performance. It is not always possible
to hear compression on small speakers. Always check an alternate
set of monitors, preferably a more accurate system, to make sure
you can stand to listen to all the details, as well as the compression
artifacts. (Wink-wink. Nod-nod!)
dug up a DAT remix of a 24-track project originally recorded
20 years ago and recently re-mixed on a Soundscape workstation.
The song, "I Move Easy," written and produced by guitarist
T.J. Tindall, had a slow almost N'awlins-style groove. The session
players comprised the main rhythm section for many of the Gamble
and Huff projects that came out of Philadelphia back in the Seventies.
The vocalist was Willie Chambers of the Chambers Brothers.
re-mix, the breakdown was too soft relative to the meat of the
track. The OCL-2 was first in the chain, using preset four (the
faster program-dependent setting) and a 5:1 Ratio. The goal was
to raise the breakdown up to the level of the main section of
the song. It worked, though it would have been more perfect had
I added side-chain EQ. (A low frequency roll-off would have desensitized
the OCL-2 when the bass came in about midway through the breakdown.)
problem solved, I was still wishing for more Release time to
bring out more of the natural room sound. The track was very
precisely mixed, with a punchy kick and snare up front (the latter
with an early Kevlar head giving it a monstrously dead 'thwomp')
but the real room ambience was a bit too far back.
of asking for more from the OCL-2, I added
the 6386 in the Fast mode. Reducing the Threshold - until the
gain reduction meter was just beginning to show signs of processing
- instantly made the track open right up. I felt like Moses conducting
the Red Sea! After finding the magic settings, the tracks became
"one" and more alive without losing impact and without
attempts at using FAST mode failed because I was looking at the
amount of gain reduction instead of listening. If the meter could
be more sensitive in FAST mode, and/or perhaps augmented with
a multicolored LED, it would give the necessary user-feedback,
the knowledge that work was actually being done.
DIALING FOR DOLLARS
luxury of using both units together was not lost on me.
I am very aware of the price for each, which is comparable to
other low-volume pieces of quality outboard; together, they're
still about one-third to one-quarter of the street price for
the beloved Fairchild. The combination
of Pendulum OCL-2 and the Pendulum 6386 kicked sonic ass, and,
as a new dad I can comfortably say it wiped it clean and changed
its diaper! I was completely comfortable using both with no fear
of signal degradation.
cases, I was so thankful for the BYPASS switches, which are not
common on vintage products (and even some modern units). Having
both units in the signal path allowed me to compare identical
settings. With slow attack and fast release the response was
similar, but in FAST mode, the 6386 is more responsive.
has the absolute minimal signal path with enough speed if need
be (certainly faster than any other optical processor). Though
not as quiet as the 6386 it has gobs of headroom. (Maximum out
is +35 dBu into a hi-Z load, +24dBm into a 600-ohm load.) Faster
yet is the 6386 with more support circuitry but no detectable
difference in the sonic texture. (Maximum out is +27 dBm in to
a 600-ohm load.) Maximum gain reduction is only 12 dB for the
Variable-Mu design, while the optical is capable of 27-dB. I
did not test either of these units on individual tracks - consider
this more of a mastering-style review.
In my conversations
with designer Gualtieri, one comment that really stuck was his
description of the physicist's philosophy as being, 'in search
of the truth.' In scientific terms, it means the ability to repeatedly
conduct an experiment and get consistent results. In audio terms,
this translates to a product's ability to consistently deliver
the goods - something the 6386 certainly does. The Pendulum 6386
Tube Limiter is good sound, clean science.
EQ Lab Report
MANUFACTURER: Pendulum Audio, Inc.; PO Box 339, Gillette,
NJ 07933; Vox: 908-665-9333 Web: http://www.pendulumaudio.com
e-mail: info@ pendulumaudio.com
APPLICATION: Audio Dynamics Processing
SUMMARY: Stereo (or Dual-Mono) compressor / limiter
with vacuum tube front-end followed by high performance opamps,
biased Class A for low distortion. I/O connections: transformer-balanced
inputs, active-balanced outputs, both on XLRs. In addition, 1/4
inch TRS side-chain access. (Transformer-balanced outputs are
available, but not recommended.)
STRENGTHS: Three Response modes: Fast, Preset (4 are
"normal" plus 2 "program dependent" settings)
and Manual (front panel Attack and Release controls); in addition
to a Bypass switch, the output is normally bypassed until the
unit warms up and voltages are stabilized.
WEAKNESS: The Gain Reduction Meter needs (and may get)
expanded range to more accurately reflect the amount of processing
when in FAST mode.