In the mid-1990s, Sony Oxford released the OXF-R3, a megaexpensive, no-compromise high-end digital audio mixing system that was later known simply as the “Oxford console.” Virtually every component, DSP and piece of software code was conceived, designed and built completely in-house because, at the time, it was impossible to buy DSP technology with enough power. As technology became cheaper and more powerful in the years that followed, Sony Oxford's focus turned to leveraging the console's distinctive-sounding software technology into the vastly growing world of affordable digital audio workstations. The company has released TDM and TC PowerCore versions of the Oxford's EQ, Dynamics, Inflator, Transient Modulator and Restoration tools. The most recent addition to that list is Oxford Limiter.
Employing logarithmic sidechain processing along with a rather exciting approach to adaptive timing functionality using look-ahead techniques, Oxford Limiter isn't your standard stereo single-band limiter. The designers have thought this thing through from a distinctly musical perspective — not one merely set on ultimate loudness at all costs — incorporating several key and innovative functions that allow you to be surprisingly creative and artistic with a limiter.
Currently available only for the Digidesign Pro Tools environment, the plug-in is compatible with Mac- and PC-based HD, HD Accel and Mix systems (TDM, RTAS) as well as LE (RTAS). My review system was an Apple Mac G5/dual 2GHz equipped with 2 GB of RAM, Mac OS 10.3.8 and Pro Tools|HD 3 Accel hardware. I auditioned the plug-in in both Pro Tools 6.9 and Apple Logic Pro 7.1 running in DAE mode. With Oxford Limiter as a TDM, you can get a max of four mono 48kHz or two stereo 48kHz instances on a single HD Accel DSP chip. This is halved in 96kHz mode, or you can achieve one mono or stereo instance per DSP in 192kHz mode. On HD systems, a single mono or stereo instance is available per chip in 48 or 96kHz modes. On Mix systems, only 48kHz operation is supported, with a single instance per chip.
Arranged into three blocks, the plug-in comprises four main cascaded processes. First is an Input and Pre-Process gain-control section, where gain-scaling compensation is conducted. Next is a program-enhancement and overshoot-control section. Following that are Output metering and dithering. The GUI is clearly mapped to this signal chain in a left-to-right fashion. At far left is a standard-looking Input section with an Input Gain fader reaching from -18 to +18 dB. The threshold for the onset of dynamic gain control action in the Pre-Process section is fixed at 0 dBr; therefore, a possible 18 dB of gain reduction is available from a full level input signal. Conversely, you have tons of headroom to pummel weak signals with heavier doses of compression. Incidentally, all faders in the plug-in provide numeric displays at all times for feedback as well as to allow settings to be typed in manually. A precise 41-segment meter displays the effective input level from -20 to +18 dBr; any levels showing up on the meter scale above 0 dB are subject to dynamic gain control. The red overload indicators monitor the input-signal levels, regardless of gain settings, providing input overload warnings at all times.
Located in the Pre-Process section are Attack and Release faders, each with a range of 0.05 to 1 ms. These controls allow Oxford Limiter to home in on virtually any program material and treat attack transients separately from sustained material. The fault with most limiters is that they hit all dynamics unilaterally, all too quickly pinning transients and subtle dynamic detail — the end result being extremely harsh and choppy sound. With provisions to fine-tune attack and release times, you can now choose what gets processed and what doesn't. Just as you're familiar with how setting the attack slower on a compressor retains more of the source signal's natural character, protecting it from harsh envelope clamping, lengthening the time of attack on Oxford Limiter allows more of the program subtleties to go unlimited and therefore without the artifacts.
Adjusting the release time similarly opens or closes the loudness valve, if you will; keeping it shorter produces greater perceived loudness. Together, the Attack and Release controls result in the plug-in being able to provide precise control of peak levels while also increasing the volume, density, presence and overall smoothness of your music. A variable Soft Knee control adjusts the soft-limiting threshold from 0 (hard limiting) to 10 dB (maximum soft limiting). At higher settings, this can improve perceived quality, as it acts like a variable ratio compressor.
Completing the Pre-Process section, a shorter 21-segment meter permanently displays, in green, the total peak Gain Reduction; the Auto Gain switch introduces automatic gain-scaling compensation to accommodate for wider input-level variations caused by excessive amounts of short-term peaks. In this way, you're able to dedicate the Attack and Release controls for the handling of fast recovery times on short-term events, with the Auto Gain managing longer events. A wonderful complementary function, it dramatically improved the gel factor when limiting highly detailed material.
ENHANCE AND RECONSTRUCT
Located within the Output panel is the Enhance section — the secret weapon that tames sample-value overs and provides overall program loudness. Because a long attack time in the Pre-Process section has the potential to allow program transients to pass right on through and escape hard gain reduction, these overshoot peaks are retained rather than clipped like in a conventional limiter and passed on to the Enhance section, where their sonic signatures can be added to the final program sound.
The Enhance fader controls the level of dynamic enhancement and overshoot protection from 0 to 125 percent. At 100 percent, complete sample-value limiting occurs whereas settings from 100 to 125 percent progressively increase loudness and program density at the expense of increasing potential distortion artifacts. (These artifacts may be desirable, depending on your production style.) Through a combination of slower attack times and the enhancement process, I was able to include all of the fine transients and detail into the output program that would normally be removed by conventional limiters. Pushing the Enhance slider toward maximum enables you to generate extreme volume loads and apply an extra punch. When the enhancement is disabled, the Pre-Process section can be used as a conventional leveling section in its own right.
Located next to the Output Level fader, whose range is from -20 to 0 dBr, is the reconstruction-metering section, capable of displaying output levels in several modes, including standard RMS and RMS + peak hold in normal or reconstructed definitions. When the Recon Meter selector is in, the meter displays reconstructed program levels — in other words, the signals that would occur in the analog domain after decoding with a digital-to-analog converter. How awesome and handy is that?
Two methods are provided to avoid or repair reconstruction errors. The Auto Comp button automatically compensates for reconstruction errors by adjusting the output level by only the minimum amount required and for only the duration of the error. In this way, the loudness of parts within the program unaffected by the errors remains as high as possible. Alternatively, you may correct for errors manually by simply reducing the Output Level fader setting by the same amount as the maximum error level reported on the meter. When left “uncorrected” (Recon is out), the overload region is displayed in red. Being a mastering-class plug, the metering is expectedly excellent. In fact, I often ran the plug-in across my stereo bus with limiting bypassed, making use of it strictly as a high-resolution precision level meter (the ones in DAWs are notoriously off).
Just as I was wrapping up my review, Sony released an update that sees the addition of a Safe Mode switch to the Pre-Process section. Employing this, the action of the Enhance section is repurposed to continuously control peak-signal modulation, rather than effect amount, to avoid red-light overs of sample value under any circumstance. This allows you to freely explore an even wider range of timing settings without the risk of clipping — regardless of attack or release times. Even with Safe Mode off, because the plug-in now has extended internal-level headroom, you can use the Output Level control to compensate for any artistically intended overshoots without fear of causing internal signal clipping. It should also be noted that, due to processing-load restrictions, the Recon Meter and Auto Compen(sation) options are disabled in HD Accel 192kHz and HD 96kHz modes.
FEEL THE HEAT
I ran an awful lot of material through Oxford Limiter during the course of my review — not so much for purely review purposes (hey, I can't lie), but more because I couldn't believe how sweet it sounded on everything. I kept wanting to explore my old tracks, both mastered and unmastered, and I not only heard improvement to previous limiting attempts but also discovered completely new sounds within the old tracks. Put it this way: Oxford Limiter can be mild-mannered, pretty and completely transparent to simply produce more emphasized mixes if that's all the tune calls for. But with minimal effort, it can also break out the balls and put them squarely to the wall.
A quick scan of the 44 presets should give you some idea of just how flexible this limiter can ultimately be. Bass Distortion, Crunchy, Hot & Pumpy and Slammer reek attitude while Brickwall, Enlarge, Fatten, Gentle Master and Classical fall into the one-touch-mastering category. The inclusion of 24-bit and 16-bit master dithering with user control of depth is a feature I'm pleased to see. Overall, I found Oxford Limiter's nouveau implementation to be absolutely brilliant. I was consistently amazed by how punchy — but also how true — the output signal sounded to the original. The sonic quality and dynamic range that are kept throughout even the most brutal of limiting are simply awesome.
OXFORD LIMITER > $530 (TDM); $350 (RTAS)
Pros: Exceptional program loudness and limiting control capable of extreme volume and punch. Variable Attack and Release controls. Dynamic Enhance and Reconstruction functions. Precision metering. Mastering-class dithering to either 24-bit or 16-bit. Supports sample rates as high as 192 kHz on HD Accel.