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RNDigital D4
An unusual plug-in provides an innovative approach to sculpting the dynamics of digital audio, but NIGEL JOPSON finds he has to read the manual.

Getting software programmers to code an audio compressor for DAWs was always going to present a problem, just because of the limitations of the device name. The descriptive terms of threshold and ratio translated all too easily into the digital domain; the magic of groovy make-up gain less so. The RNDigital D4 is perhaps the only compressor plug-in to offer the ability to dynamically lift instruments in a busy song in the ‘make-up gain’ manner of the hardware classics –- albeit with more than two knobs to twiddle! Think about lifting the initial scrape of plectrum on string of a power chord without squashing the sound of a Marshall, or bringing out the second-fnger plucking from a classical harpist. It’s the sort of plug-in that’s perfect for lifting a vocalist’s lower-pitched verse without slamming the full-on performance of the chorus. The D4 accomplishes such tasks with a unique design and an interface based around a dynamic input/output map.

At first glance the D4 resembles a multiband compressor — it’s not — and the manufacturer is careful to fag this up straight away. Yes, you need to read the manual. Even though I’ve used this compressor since its early incarnation as the Neodynium (from developers Elemental Audio), and even though I own the Dynamizer which it was re-badged as, I still found I had to have a quick peek. The Dynamizer interface has completely changed: the new design takes up less screen space, does away with the daft and tiny ‘advanced’ button that delivered full access to controls, and adds some useful extra metering and tweaking functions. The new look of the interface more clearly implies the spirit of operation, which is as an instrumentation-type device.

The four possible bands of the input/output map (blue, orange, yellow, green) represent gain sectors of the audio dynamic range. It’s like a bargraph meter for a channel, with four compressors for each gain range. The compressors have Attack/Ratio/Release sliders at the bottom of the plug-in interface, the kicker feature is that the ratio range can be set as less than 1:1 — a particular segment of the gain range can be expanded upwards or downwards, to occupy more dynamic space. The left and right ‘handle’ sliders for the four sections of the I-O map allow these adjustments. It’s very easy to make an ordinary drum track sound extremely ambient — sucking up all the small refections from the room in a similar manner to the SSL listen mic compressor — but without all the distortion and peak limiting. This involves pulling the lower gain ranges up on the ‘out’ side of the map. Skewing the gain map in the opposite direction, I’ve found the D4 handy for removing parts of a kit from a drum loop sample. Hihats are easy to almost completely mute, as they’re generally mixed much lower than kick and snare. The D4 is often able to take a snare out — or right down — in a much more musical way than a noise gate would, and much faster than a lot of slicing and dicing with an editor.

The D4 is able to take an over-limited/compressed recording and expand the top ‘in’ section (say 0 to -6dB) downwards to occupy a greater range at the ‘out’ section (say 0 to -12dB). Working on a well overcooked mix, I found I had to be quite ambitious to restore some life to the dynamics. Modern digital compression/limiting crushes so much information into the top 3dB of a mix … but this is hardly news to Resolution readers.

D4 release times need careful adjustment with downward expansion or the result will be stuttering audio. I found dialling in super-long releases delivered a more natural sound than relying on the auto release button. The outcome was a more open sounding track — the big surprise to me was how much the D4 restoration process boosted a vocal in the mix. When expanding audio dynamic zones downwards, a problem arises: what to do with low-level audio that already exists in the area we are expanding into? Reducing the gain of low level audio below the expanding zone proportionately (the default behaviour of D4) will result in a loss of ambience. The D4 coders have come up with some new buttons labelled ZGC (Zone Gain Control) to fx this conundrum. Clicking the up/down arrows to turn the ZGC colour from blue to grey will result in audio above/below expanded zones being merged with audio that has been stretched into the output space it formerly had all to itself. So a tambourine mixed at -24dB will still be output at -24dB, even if louder audio has been expanded down into this area.

In a similar manner, it’s possible to achieve the reverse and pull up lower audio levels to deliver a fuller sound: with this approach I was able to give a live Weather Report song a more modern and dense sound, but without compressing the peaks of the 1970s recording (merged with the ‘up’ ZGC button).

The D4 has its own useful peak limiter with three attack times, but in a mastering situation it’s probably better to follow the D4 with a dedicated limiter plug-in, such as the RNDigital Finis. When I found the Weather Report high frequency percussion elements were lifted too much, I was able to use the D4 input flter to trim the HF effect of this ‘bootstrap compression’. Clicking the button of the interface replaces the Zone I-O map display with the input flter controls. There’s a wide-ranging 3-band equaliser, and the soloed results of EQ or dynamics processing can be monitored. I like the provision of an overall +/-20dB gain trim, which makes it easy to vary the infuence of the sidechain after adjusting EQ. The midrange peak control of the flter can be set with a narrow Q, enabling the D4 to be used as a very capable de-esser. The D4 (download US$249) stands out because it approaches audio in a refreshingly new manner. It would not be my tool of choice for crushing or saturating peaks, but the D4 tackles the tricky task of serious dynamic digital audio surgery in a transparent and intelligent manner, and is possibly the only plug-in able to restore dynamics for over-compressed audio. The D4 is at its best when automatically adjusting an instrumental performance, de-essing a vocal, twisting the vibe of a prerecorded loop, or used as a bootstrap compressor or dynamics restorer.

Contact: RNDIGITAL LABS,
Us:website: www.rndigital.org