Recording

dbx DDP: DIGITAL DYNAMICS PROCESSOR

The last couple of years have seen the birth of several cost-effective, all-in-one digital dynamics processors loaded to the gills with algorithms for

The last couple of years have seen the birth of several cost-effective, all-in-one digital dynamics processors loaded to the gills with algorithms for tracking, mixing and remastering. dbx's DDP Digital Dynamics Processor breaks an astonishingly low price point ($599, plus an extra $199 for the digital I/O option), while boasting pro features such as balanced analog I/O, 24-bit converters and digital throughput with dithering. My aching Visa card begged me for further investigation.

GETTING TO KNOW YOUThe 1U, rackmountable DDP offers a plethora of processing algorithms, including compression, limiting, expansion/gating, de-essing, and 3-band parametric EQ. Both dual-mono and stereo-linked operation are supported.

The rear panel offers both XLR and 11/44-inch TRS connectors for balanced analog I/O. The digital I/O option adds both AES/EBU and S/PDIF I/O to the rear panel. But there are no word clock connections, so multitracking with more than one unit in the digital domain is not feasible. Analog and digital outputs are always hot, but you must switch between analog and digital inputs. MIDI In and Out/Thru connectors facilitate MIDI Program Changes, parameter control and bulk dumps/loads. The AC cord is detachable.

The front panel sports 16 buttons for accessing the different algorithm chains, parameters and utilities (plus a bypass button for the digital processing), and a data wheel for programming. A generously sized LCD screen shows a wealth of info, including the program number, chain configuration of processing blocks, parameter values, digital I/O and gain reduction metering, stereo link status, threshold indicators for each processor in the chain (nice!), and a graphical representation of your current dynamics or EQ setup.

Four wide-ranging analog I/O gain knobs accommodate both +4 and -10dB line levels without a sensitivity switch. As we'll soon see, this is not necessarily a good thing. The knobs are detented, allowing repeatable settings. The two eight-segment meters above the gain pots can be independently switched to show either analog input or output levels for each channel.

Digital input level (-12 to +12dB range) is set via the Utilities menu. There is no dedicated control over digital output levels. But, you get simultaneous temporary peak-hold and average metering in the digital domain. The sync source may be set for internal crystal, AES/EBU or S/PDIF, and the sampling frequency to either 48 or 44.1 kHz.

I'M IN CHAINSThe learning curve for the DDP is much steeper than it needs to be, due to an applications-driven design philosophy geared toward semipro users. There are 50 factory programs, along with 50 RAM slots for user programs. A program consists of separate (or linked) left- and right-channel "setups" such as the factory Bright Snare and Low Strings that suggest predetermined EQ and dynamics settings for specific applications (as if that's possible). Many of these set-ups use the same algorithm chains and differ only in their parameter values. When you save a program, you're only storing the algorithm chain configuration and not any parameter values-you must also save a "setup" in order to store parameter values.

Thankfully, a default setup is provided for each and every chain configuration, for those who wish to start with parameter values set to zero. But professionals will cringe at the tedium of having to title and store the algorithm chain in addition to the parameter values for that chain, especially because you can't change the order of the processing blocks in the chain, so you're always naming essentially the same thing. And because our industry's convention (outside of MI products like synths) is to name only programs, there's a danger that confused users will not label each setup with a unique name and will unintentionally overwrite all parameter values for all other programs that share that setup name!

The algorithm chain order is: EQ, gate, compressor, de-esser, limiter. But some setups omit one block, and you can always turn off individual blocks in a chain. Version 1.3 software adds three algorithm chains that include dither, which you can set to 16-, 20- or 24-bit word lengths. The dither replaces the de-esser (so you can't use both simultaneously) but, of course, is placed at the end of the chain.

ANALOG PUNCHThe DDP places dbx's Type IV[superscript]TM Conversion Process, which is essentially a soft clipper with noise-floor enhancements, before the A/D converters. Available only on the analog inputs, the clipper allows you to hit the DDP with a very hot signal without fear of generating digital "overs."

The clipper's threshold is set at 4 dB below the top of the A/D's input range. Unfortunately, you can't bypass the clipper and there is no makeup gain for the clipper itself, resulting in an output approximately 4 dB below full-scale. You must therefore increase the digital compressor section's output gain to bring your digital output up to 0 dBFS (a 1:1 ratio is offered if you don't want additional compression). But when using the unit's bypass button to do A/B comparisons, you lose the 4 dB of makeup gain, making comparisons difficult at best. A bypass provision for the Type IV clipper would solve this problem, but the extra analog circuitry required would raise the price of the DDP considerably.

On the positive side, the clipper sounds great on rock, country and blues, giving you a hotter, punchier sound. As one would expect, however, it's not appropriate to use on classical or chamber music, solo flute pieces and the like.

I also found the DDP's analog input sensitivity to be set too high for pro levels. You must attenuate pro levels approximately 8 to 12 dB to get internal digital input levels down into the nominal range of the unit.

Because I couldn't bypass the Type IV clipper, it was impossible to isolate the A/Ds to evaluate their performance on full-scale input. That said, the analog front end is clear and present, if a tad too present. There's a noticeable glare to the sound, but the performance for the money is outstanding.

DIGITAL PROCESSINGThe DDP's 3-band parametric EQ could stand to be more flexible, offering only 11/43-octave ISO frequencies and no shelving capabilities. However, the Q range is broad enough to handle both broadband tonal shaping and notch filtering (again, provided the problem sits right on an ISO frequency). Unfortunately, the EQ sounded cold and thin to my ears.

The EQ can be inserted in the DDP's sidechain for frequency-conscious dynamics processing. However, the sidechain is global, serving the gate, compressor, limiter and de-esser at once. This all-or-nothing approach, along with the EQ's bell curve characteristic, limits the EQ's sidechain applications. Lowpass and highpass filters, or shelving EQ, would be more serviceable for frequency-conscious gating in particular, and the DDP is not always successful in this application. However, the DDP's gate performs well for general purpose downward expansion and gating.

Included in the EQ section is dbx's TSE[superscript]TM, or Tape Saturation Emulation, process. TSE provides a logarithmic mapping of the input to the output at the top of the unit's headroom, plus a choice of four variations of tonal shaping. To my ear, the darker settings take away air and detail and the brighter settings make the sound more brittle and icy. Arbitrary tonal shaping isn't my cup of tea, and I suspect that most pros doing critical recording will want to turn the TSE off and use a good multiband equalizer to fine-tune their tracks and mixes. Hobbyists may appreciate the instant gratification that the tonal variety provides.

All of the DDP's dynamics processors have access to dbx's Transient Capture Mode, or TCM[superscript]TM. TCM delays the audio signal, by a user-programmable amount, from 0 microseconds to 3 ms. This gives the dynamics processor a chance to react before the attack of the sound, giving in effect an instantaneous attack time. TCM is global, so it is applied simultaneously to all dynamics processing.

The compressor, gate and limiter all offer a wide range of parameter adjustments. I especially appreciate the fine increments in the ratio and threshold values. However, there are so many steps for attack, hold and release that a fresh glass of milk can go sour before you scroll from one end of the range to another! For example, do we really need 110 steps between .1 ms and 200 ms compressor attack time? No matter how good the quality, I worry about the data wheel wearing out a couple of years down the line with so much spinning required. I've seen it happen too many times on all sorts of gear.

When set up with care, the DDP's compressor can handle percussive material with broadband spectral content without pumping. Using low ratios and high thresholds, the sound is clean and transparent. At .1 ms attack time, however, the compressor sometimes distorts on transients, even with long release times.

Both hard-knee and OverEasy[superscript]R compression are offered, the latter providing a range of ten progressively softer knees. Auto and manual compression modes are also included. Where heavy compression is required, manual control of attack, hold and release times is a must. Auto mode, as well as harder knees in manual mode, can cause very noticeable pumping.

I was not impressed with the DDP's limiter, which offers only a .1 ms minimum attack time, leading to routine transient overshoot. The limiter pumped noticeably when pressed to deliver only 4 to 6 dB of gain reduction and, even with moderate to long release times, tended to distort on percussive transients. When using the DDP's A/Ds, my recommendation is to turn off the limiter and stick with the Type IV clipper, a much better performer.

The DDP's de-esser was a pleasant surprise. While remastering a folk album with the DDP, I found that the de-esser reduced sibilance on a female vocal without pumping or leaving "holes" in the mix, an impressive feat.

CONCLUSIONSThe DDP performs well with moderate amounts of digital processing and slower attack and release times. But for more rigorous applications, the DDP is probably not the best choice.

The analog Type IV clipper sounds great and is, in my mind, the DDP's best feature. But the fact that you can't bypass the clipper limits the unit's use as an A/D converter mostly to applications involving popular forms of music. The DDP is best suited to the engineer or hobbyist who works mainly with -10dB level equipment and deals strictly with popular music. For this type of user, the DDP's affordable pricing and numerous features should prove attractive.

dbx, 8760 South Sandy Parkway, Sandy, UT 84070; 801/568-7660; fax 801/568-7662. Web site www.dbxpro.com.

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