Rupert Neve Designs Portico

We take another look at the impressive Portico range, focusing on a compressor-limiter and a unique tape-emulation processor.

Mr Rupert Neve's Portico modules are the latest incarnations of a lifetime's development of analogue circuit design. In the April 2007 edition of Sound On Sound I reviewed the Portico 5012 Dual Channel Mic Preamp and the 5033 Single Channel Five-Band Equaliser. That review features the background and history of Mr Rupert Neve's designs and the aims of the Portico range, so I won't repeat myself here.

This review tackles another pair of Portico series modules: the 5043 Two Channel Compressor-Limiter and the 5042 Duo Line Amp and Tape FX. The latter is probably the most talked-about unit in the range, since it incorporates an innovative 'True Tape Emulation' mode.

5043 Compressor-Limiter

The Two Channel Compressor-Limiter does exactly what it says on the box. It is a relatively simple to use, well-specified unit, clearly designed for the discerning professional, and it provides a clean, musical-sounding means of controlling programme dynamics through sophisticated VCA technology.

The module's form factor is the same as the other Portico modules, being shipped as standard as a 1U-high, half-width rack module to suit conventional desktop and rack mounting. Alternatively, a vertically-orientated face-plate is available for installation in the bespoke Portico multi-unit rack or the new 5088 mixing console. The chunky, folded-steel case helps to minimise electromagnetic interference while also giving the unit a very sturdy, robust quality that will ensure it lasts a lifetime.

The rear panel is equipped with line input and line output XLRs for each channel, the latter capable of delivering a generous +25dBu. Both the input and output connections are via transformers, to provide a true earth-free floating connection with complete galvanic isolation.

The connectivity of the 5043 differs from most of the other Portico units, in that it has a second set of inputs. A pair of TRS quarter-inch sockets labelled Bus In A and B provide mix summing inputs. The idea is that the outputs of numerous Portico input or EQ modules can be linked together using their Bus Out sockets. This forms a summing bus that is processed via the Bus In sockets on the 5043 — although the 5014 Stereo Field Editor is also equipped with a mix-bus summing amp. It's a neat idea, making it possible to construct a very high-quality, fully functional mixing system from a bespoke collection of Portico modules.

However, it is worth noting that these Bus inputs can't really be used as alternatives to the main XLR inputs. This is because the output impedance of the source will affect the gain through the mix amp. For unity gain mixing, 10kΩ is required, and most sources have a much lower output impedance than that. Consequently, the summing amp will typically boost the input signal by between 25 and 45dB, which probably isn't what you want!

The 5043 Two Channel Compressor-Limiter not only sounds great but has a novel metering system that saves time and hassle.Photo: Mike CameronAnother two quarter-inch sockets are wired in parallel and these provide a linking bus for external compressor side-chains. Multiple 5043 compressors can be linked together in this way to provide multi-channel dynamic control. Usefully, the control voltage format used here is completely compatible with other Rupert Neve designs, such as the very nice (but sadly, now discontinued) Amek CIB and DMCL units.

Finally for the rear panel, there is a coaxial power socket and an on-off button. The unit is supplied with an in-line switched-mode power supply, which provides 15V DC. Inside the Portico module, a DC-DC converter provides the balanced ±17V power rails required by the circuitry. Apparently, this converter is capable of operating correctly with an external DC supply of between 9V and 18V, so it is possible to run the modules from a car battery for location applications.

Moving to the front panel, the control legends are printed on a plastic film escutcheon, recessed into the panel to provide a very neat and hard-wearing finish. The two channels are equipped with identical controls laid out in an intuitive manner, and with a reasonable amount of space to get fat fingers around them. All of the rotary controls are continuous potentiometers, and without detented positions to help reset favourite configurations accurately. That's not really a problem in a console application, but it makes the unit less attractive for mastering.

Starting at the left the Threshold, Attack, Release and Make Up Gain controls run across the bottom of the panel, with the Ratio control sitting above, in line with four illuminated push buttons. The first of these switches the compressor function in and out of circuit, but the input transformer, line driver and output transformer remain in the signal path. The next button reconfigures the compressor side-chain for a feed-back topology instead of the default feed-forward mode (more on that in a moment).

The third button connects the side-chain control voltage to the link bus, which is shared between the two compressors in the module, as well as to the two rear-panel sockets. The final button selects the rear-panel (mix) Bus Input as the compressor's signal source instead of the XLR line input.

Across the top of each module is an LED bargraph meter. The left compressor meter always shows the output level (with the LED bar building from the left in the usual way), while the meter above the right hand compressor always shows gain reduction (with the bar working back from the right). A push-button nestling between the two channel sections swaps the signals feeding these two meters to monitor either the left or right channel.

The metering on most compressors is switched individually on each channel between output level and gain reduction and initially — it was an unfamiliar approach — I didn't like the Portico arrangement. However, as I used the unit more, I came to realise what an inspired decision this was, and it dawned on me that as I was adjusting the compressor I was actually balancing the gain reduction and output levels simultaneously — because I could see both at the same time. On most compressors I'm always having to swap between the GR and output meter modes when optimising the controls. The Portico solution means you only have to press the button when you want to set up the other channel, which is an easier and faster way of working.

The parameter control ranges are all very practical and sensible. The Threshold can be adjusted between -36 and +22dBu, while the Make Up Gain offers -6 to +22dB. Attack is variable between 20 and 75ms, and Release is from 100ms to 2.5 seconds. The Ratio control spans unity 1:1 up to 40:1, which I think we can safely call limiting! This is all pretty standard fare but, interestingly, while playing with the unit, I found that the settings I tended to use the most had all the knobs pointing more or less straight up! Whether by design or good fortune I don't know, but this makes it very easy to set a reliable default starting point. Setting all the knobs to point straight up provides a threshold of 0dBu with a ratio of 2.5:1 and 4dB of make up gain. Attack time is about 45ms and the release is 400ms, which is pretty much a standard ball-park starting point for working with vocals!

Sound Quality

As compressors go, the 5043 is very clean sounding, as you would expect a modern VCA design to be. In fact it uses the THAT 2181 VCA chip, which is a sophisticated development of Blackmer's famous Dbx designs.

However, it would be wrong to suggest that the 5043 was entirely neutral. The input and output transformers definitely impart something of a larger-than-life quality to the sound, and that is the hallmark of true high-end gear. Switching the compressor out of circuit still retains the body, sheen and gloss in the sound.

The fun really starts, though, when the compressor is switched in. The feedback arrangements provide two significantly different dynamic responses and, in effect, this provides two compressors in one. The default feed-forward mode configures the side-chain to work from the input signal, which means it can respond immediately to changes in input levels. The result is a fast-acting response with very precise control of levels. Not surprisingly, most protective limiters are designed to work in this way.

The alternative feed-back configuration takes the side-chain input from the output stage, which is a far more common technique and was employed in most vintage compressor designs. This approach tends to provide a gentler, more subtle form of dynamic control because the output has to change in level before anything can be done to correct it.

Essentially, if you want accurate, fast control with a punchy, bright, dynamic sound, feed-forward is the starting point. If you want a softer, more organic kind of compression, the feed-back mode is a better place to start from. Switching between the two modes is instant, but I found the subjective results can be misleading, as the controls (especially the attack and release times) need to be re-adjusted to achieve similar dynamic effects and optimise the results.

With two compressors in the one box, this Portico module can be used to process a stereo signal. However, not only is it necessary to activate the Link bus on both modules (to tie their side-chain control signals together), but it is also vital to ensure identical control settings across both channels. Failure to match the channels won't produce stereo image shifts — the shared side-chain control voltage takes care of that — but it will cause different dynamic responses depending on which channel is driving the control voltage bus at the time.

You can also employ the Link mode to use one compressor as a 'ducker', controlled from its neighbour. This could be used to enable the lead vocal, say, to dip the level of a guitar track. In this configuration you can give the two channels completely different settings, to achieve the desired results.

In feed-back mode, I found the 5043 worked superbly as a stereo bus compressor, helping to glue mixes together in a very refined, polished and extremely effective way. The sonic colour the Portico unit adds to the sound doesn't change dynamically (unlike some compressors) and dynamic manipulation always sounds remarkably transparent and natural, even when being driven hard. For mastering applications I found the unit worked very well as a protective peak-limiter in feed-forward mode, providing excellent level security while simultaneously warming up the sound in a really nice way. In feed-back mode, the level of control was adequate, but not as good as the feed-forward mode, especially with transient-rich sources such as percussion and plucked acoustic guitars. But this configuration worked very well to help shape and control signals more creatively. Whether for vocals, bass guitar, drums or whatever, the 5043 just gets on with the job to deliver a well-controlled, musically-appealing sound.

For tracking individual channels, I found that coupling the two channels together provided a foolproof solution. The input was fed to the left channel, set up as a feed-back compressor to provide the required degree of dynamic control. The output of the compressor was then linked straight across into the right channel, which was set up as a feed-forward limiter, to keep any fast transients in check. The output to the recorder was taken from the right channel's output. Setting the right channel up with the maximum ratio, minimum attack and release times, and a high threshold (set just below the clipping point of the recorder) provided an extremely effective limiter. The Link switch was left off on both channels because I wanted the two dynamics processors to work on the signal independently.

Overall, then, this is a very nice unit indeed (as it should, be given the price) and it provides superb dynamic control, which is transparent and artifact-free in operation, yet bestows some welcome scale and musicality to the signal in a typically Neve way.

5042 Line Amp & Tape FX

The 5042 Two Channel 'True Tape' Emulation and Line Amplifier module follows the same basic pattern as the other Portico units. Power is provided by the same external in-line, switched-mode PSU, and the same half rack-width 1U chassis is employed.

At its core, the unit is a simple, no-frills line input stage, with variable input level and the ability to route the output to a mix bus if required (there is no pan facility, though). The rear panel features XLR connectors for the line inputs and outputs — all via transformers, of course — and there are also two pairs of quarter-inch TRS sockets that provide the mix bus in and out linking for each channel.

The 5042 Line Driver and Tape FX processor offers a unique and very convincing emulation of a tape machine's electronics.Photo: Mike CameronThe front-panel controls for the line-input stage are trivially simple: a rotary level control provides ±12dB of gain trim and an illuminated push-button allocates the output signal to the corresponding mix bus socket. There is also a bar-graph meter to monitor the input level, reading from 0dBu to +22dBu. All very simple and straightforward, and my only quibble is that there is no centre detent on the level control for unity gain. However, the really interesting thing about this unit is its 'true tape emulation' facilities, and the majority of the controls relate to this functionality.

A push-button activates the tape emulation circuitry and another changes the mode to simulate tape machines running at 7.5 or 15ips, while a large rotary control adjusts the amount of 'record level' and hence 'tape saturation.' As this input drive is increased, the output level is simultaneously decreased, to maintain a consistent gain through the process. A third button allows the bar-graph meter to be switched to show the drive level of the tape-emulation circuitry — in effect, how hot the 'tape' level is.

Of course, there is no real tape inside this little box, but there is a very clever emulation of the relevant parts of a real tape machine's electronics, including the constant current drive to the tape heads (inductively coupled coils are employed to replicate their key attributes), and the replay equalisation. The result is a complex non-linear circuit that introduces considerable amounts of low-frequency distortion (predominantly third harmonic), compresses progressively with high-level signals, and introduces subtle frequency-response anomalies such as a 'bulge' around 300Hz and some characteristic high-frequency (HF) ringing.

Although thought of such deliberate audio mangling is anathema to the pro-digital brigade, this is what even the best analogue tape machines do, and a lot of people subjectively like the resulting effects. The advantage with the 5042 module is that the user can decide whether to apply the effect or not, and how to optimise it for a particular track or mix.

On Test

I plugged the unit in to process the mixed stereo output of a range of digital recordings stored on a SADiE LRX2 system, via a Benchmark DAC1 converter. As a straight-line amp, the unit imparts the subtle-but-noticeable character common to all the Portico units — a slight richness suggesting a larger-than-life quality — which is entirely down to the use of transformers in and out, and some beefy output transistors.

Initially, switching in the tape-emulation circuitry was a little disappointing. The delicate air and sparkle of the test recording (some solo 12-string guitar work) seemed to vanish. However, it quickly transpired that this was largely because the module was set in the 7.5ips mode, which deliberately pulls the HF roll off back to 16kHz (-3dB), instead of 20kHz. This accurately replicates the reduced HF capability of slow-moving tape, but switching to the 15ips mode restored the high-end to something closer to what I had expected.

The 5042 uses inductively coupled coils to emulate the constant current drive to a tape machine's tape heads.Photo: Mike CameronEven with the Saturation control in the fully anti-clockwise position, the effect of the emulation circuitry can be heard as an extra level of subtle coloration compared with the straight-line drive stage on its own. The amount of coloration is affected by the input signal level, so setting the gain structure correctly is critical. On a technical level, winding the Saturation control up progressively increases the amount of harmonic distortion and transient compression, to produce a more and more saturated, and eventually overdriven, kind of sound. It is remarkably similar to the effect of driving a high-quality tape machine harder.

With the 15ips setting I found the whole thing very controllable and relatively subtle although, having been carefully schooled over many years in the BBC tradition of carefully managing tape levels to minimise this effect, it all felt a bit unnatural to me! However, I can certainly appreciate the quality and accuracy of the emulation, and the artistic effect it is intended to contribute.

On an aesthetic level, the tape emulation just does nice things to the sound. Mixes seem to gain some extra low-frequency weight and fullness, while also sounding more rounded and controlled at the upper end. The sharp edges of percussive sounds are sanded off in a delicate way that preserves their musicality but seems to indefinably improve their sonic character. Cymbals, in particular, sounded more polished and less edgy, and subjectively more natural, which I found rather weird: it was a something like recording them with ribbons instead of large-diaphragm condensers, in that the fizz and HF resonances were removed. I also noticed that raw vocal tracks with a tendency towards stridency and sibilance sounded smoother, more real and easier to listen to, although I found that the effect was a little too rich for my own tastes on most male vocals.

On switching back to the 7.5ips mode, the whole emulation seemed to become rather more heavy handed, and I found the useful range of the Saturation control was too bunched at the low-end, making it harder to achieve the strength of effect I sought for solo instruments or stereo mixes. I subsequently found that this problem could be improved significantly simply by turning down the input level. In contrast, if you are looking to impose a 'statement effect' on a track, you can really lay it on quite thickly in this 7.5ips configuration, and I found that you could really trowel it on with drum submixes to great effect — a return to Elvis Costello and the 1970s! Drum mixes really filled out and settled nicely into tracks, with negligible other work required. The innate compression and transient control results in a louder, bigger sound, while the harmonic distortion really fills out snare and kick drums nicely, adding a lot of body and definition. In fact, most of my standard EQ was rendered redundant.

Conclusion

Essentially, the 5042 tape emulation does what real tape does: it tends to smooth over a recording, helping to blur any rough edges in a mix and conceal weaknesses in mic technique. It seems to glue a mix together in a similar way to mastering compression (a very low ratio, combined with a very low threshold) so that everything is better controlled, but without losing relative dynamics. I don't think the 5042 can be described as being exactly the same as recording to tape, but the important positive effects are modelled very well. It's certainly a counter-measure to modern digital recording, which is pretty much perfectly linear in a dynamic sense and consistently reveals flaws in mixing or mic techniques with hideous precision.

For anyone who feels digital recordings are 'too sterile', this is an impressive antidote, but one to try for yourself. There is no doubt that it adds warmth and body to a track, and the only thing to be wary of is that correct gain staging is important to avoid clipping the saturation circuitry with high input levels, and that extreme settings also contribute a noticeable increase in the background hiss.... although for most that would just be considered part of the tape emulation anyway!

There is no doubt that this is a very clever effects unit that brings most of the desirable attributes of analogue tape to the table, in a very versatile and generally easy to use tool. No one will hate this unit, and many will fall instantly in love with it. It is, of course, very easy to get carried away and to over-use the effects it produces, but for anyone recording rock & roll in the digital domain, this is a product that will undoubtedly enhance your tracking and mixes, to deliver a more organic and analogue sound. Thoroughly recommended.