Mastering ConsoleReviews : Mixer
Designed to meet very specialised needs, mastering consoles can be scarily expensive. Crookwood’s modular system offers faultless sound quality at a surprisingly affordable price.
Mastering is a specialised sector of the pro-audio industry, with its own particular equipment requirements. For example: everything is usually adjusted with rotary switches, so that the settings are easily repeatable; passive, balanced analogue and/or elaborate digital matrices are employed to insert outboard signal processing equipment in whatever order might be required; and the monitoring controller must incorporate facilities to adjust the relative levels of monitored sources, so that the original and processed versions can be compared fairly at equal volumes. There are usually at least two distinct signal paths, too: the main ‘source’ monitoring path and the ‘transfer’ path, which incorporates the inserts and feeds the analogue or digital recording destinations.
There are several manufacturers of dedicated mastering consoles brimming with all these kinds of facilities, but generally with prices starting from frighteningly expensive and continuing up to ‘if you need to ask you really can’t afford it’! At slightly less eye-watering expense, companies such as Dangerous Music and Manley produce analogue insert switchers (the Liaison and Backbone, respectively), but even these will set you back between £2000 and £5000several thousand dollars, and you’ll still require some form of additional monitoring controller, as well as a bunch of high quality A-D and D-A converters... and probably a digital router, too. So a modest ‘mastering system’ constructed in this way would still cost as much as a decent car.
I recently found myself exploring these options for real, because I decided that I needed to streamline my own studio facilities, and a simple mastering console was the obvious solution. I often indulge in small-scale private mastering work but, more importantly, reviewing equipment for Sound On Sound involves inserting the product in a signal chain and comparing the signal source, the review equipment and possibly a reference product, to evaluate their sound quality and characteristics. Up until now I had been using a complex mishmash of equipment to achieve this, including an analogue patchbay, a Coleman Audio analogue switcher, a Z-Sys digital router, a custom-built monitor controller... and an awful lot of re-plugging! My initial exploration of the small mastering console market was quite a frightening experience, and I nearly gave up the idea. It was then that I discovered Crookwood, a small independent British company with the marketing tag line ‘bespoke audio engineering’.
Crookwood have been in business for 20 years but have a surprisingly low profile, despite having an extremely high reputation amongst those ‘in the know’ — which includes the likes of Glenn Meadows and Bob Katz. Crookwood’s founder, Crispin Herrod-Taylor, has worked previously as a design engineer for the high-end hi-fi company Meridian, as well as pro-audio manufacturers including Focusrite and SSL. He set up Crookwood to design and build his own range of modular monitoring controllers and mastering consoles, as well as impressive mic preamps (such as the innovative Paintpot), and other bespoke products. These are all essentially built to order, but at prices that don’t require the donation of surplus body parts!
After a lengthy exchange of emails with Crispin, to explore the various options and customisation possibilities — and I have to say he was extremely patient and helpful throughout — I commissioned a Crookwood M1 mastering console with a few minor customisations which, I gather, have been integrated into future consoles. After placing my order, I was reminded that a fellow SOS reviewer and mastering engineer, Eric James, purchased the company’s C2 monitoring controller a few years ago, and you can read his review in SOS August 2007 (there are some shared elements between the C2 and M1).
Racing Down The M1
The I/O side of things is handled by rack units, which keeps the desktop controller nice and compact.
The I/O side of things is handled by rack units, which keeps the desktop controller nice and compact.
The M1 is Crookwood’s ‘flagship’ stereo mastering console, not because it is the largest, but because it incorporates both analogue and digital inputs and inserts. The M2 version is digital-only, while the M3 is analogue-only, and for anyone interested in surround-sound mastering, the equivalent consoles are the M10, M20 and M30. Having chosen the basic console form, the next decision is how many insert points are required, with the options being three, seven or 11. Apparently, the seven-insert model is the most popular for commercial mastering rooms, but I opted for the three-insert version, which accommodates two analogue and four digital input sources, with three analogue and three digital inserts — the model M1-3AI. However, should requirements change, any Crookwood console can be upgraded to any other model relatively simply, thanks to a clever modular design. It’s just a case of installing new cards, control panels or I/O racks, and replacing the EPROM that stores the system configuration data.
Crookwood’s mastering consoles feature an entirely analogue monitoring path, with all signal switching and level control performed passively via sealed relays, just as it is on the Dangerous ST-SR and Cranesong Avocet monitor controllers. The active audio circuitry is fairly minimalist, employing LME49720 op-amps, which are very high-quality devices with low noise and a high slew rate. However, since the monitoring sources include digital inputs, a dedicated monitoring-path D-A is also required. This can be a suitable commercial model wired up externally, if preferred, or a Crookwood-designed module can be installed instead. Selecting a digital monitor source automatically routes that source to the D-A’s input, and feeds the outputs to the analogue monitoring path.
In contrast, the console’s ‘transfer path’ is fundamentally digital and so, to accommodate the three analogue insert points, an A-D and D-A converter pair is required to move signals between the digital and analogue domains. However, with only one pair of converters available, the three analogue inserts always work together as a block inserted into the digital path, before, after, or between the digital inserts. These transfer converters are switched into circuit automatically in a seamless way whenever the analogue inserts are enabled. The transfer path’s digital output is fed to three separate record destinations simultaneously.
In commercial studios, where it might be desired to select different converters for different roles as part of the sound-shaping process, the larger Crookwood mastering consoles have facilities to freely allocate converters from a pool of devices to serve in different parts of the signal path. For my little M1-3AI console, though, I opted to use Crookwood’s own internal converters throughout. These are SRC-based designs, similar in concept to those of Cranesong, Benchmark and Drawmer, where the actual A-D or D-A converter chip runs from a local crystal clock at all times, to ensure optimal jitter performance. A sample-rate converter chip handles the different input or output sample rates, removes external jitter, and ensures a very fast lock-up time if the digital source is changed, the last being essential where input sources are being compared and insert processors switched in and out.
The A-D converter’s clock source (internal or external) and sample rate (44.1-192 kHz) can be selected via the console’s configuration menu, while the two D-As simply follow the sample rates of their inputs, of course. In my installation, I can easily patch in my lovely old Apogee PSX100, Benchmark DAC-1 and customised Drawmer A2D2 converters, should I need different converter characters or additional domain translations.
The controller’s front panel puts all functions within easy reach, and features clear labelling.
The controller’s front panel puts all functions within easy reach, and features clear labelling.
The M1 console hardware is accommodated in two deep (480mm) 1U rackmount units referred to as the Brain and the Channel I/O rack (larger systems involve additional I/O racks). The signal routing is based around an 8x8 asynchronous digital router card and a balanced passive analogue relay input switcher and insert matrix cards. All audio connections with the racks are via 25-pin D-sub connectors, and standard Tascam-wired breakout cables can be used. However, I chose to add optional 1U XLR breakout panels, each housing 16 XLRs, to serve as a convenient integral patchbay. These XLR panels are elegantly designed, with a small printed circuit board mounted across the back of each group of eight XLRs to collate the connections directly onto a D-sub socket. Simple ribbon cables with D-sub connectors at both ends are supplied to link each group of XLRs to the relevant I/O ports on the Brain and I/O racks. This solution occupied an additional 5U of rack space in my installation, but adds a lot of flexibility.
Power for the two racks is provided by a small in-line 12V DC universal power module which is double-insulated, so a spade terminal is provided on the rear of the Brain rack for a proper technical earth connection. Inside the Brain rack, a switched-mode power supply generates the required internal audio and logic power rails, with additional local regulation on each individual analogue and digital audio card. Power and control data is passed from the Brain to the I/O rack via a short link cable with nine-pin D-subs at each end, and the front panels of each rack unit incorporate LEDs to indicate the presence of the power rails and control data.
Operational control of the mastering console is via a pair of modular and customisable panels mounted alongside each other in a neat wooden pod (they can also be rackmounted, if preferred). The right-hand panel handles the monitoring controls, while the left looks after source selection and transfer-path inserts. Both panels feature a bank of 16 illuminated push-buttons on the left, with a second, smaller set of mode buttons on the right. They also both incorporate clear blue-and-white LCD panels at the top, while the monitoring panel also features a large rotary encoder with a ring of LEDs.
The monitoring controls are truly comprehensive: I really can’t think of any functions that could be added! The top eight push-buttons on the left-hand side ‘condition’ the monitoring signal, while the bottom eight select the outputs. So there are facilities here to audition just the left or right input channel on both speakers, as well as the mono sum (mid) or the stereo difference (sides) signals. Polarity (phase) can be inverted independently for the left and right channels, or the absolute polarity can be flipped to make bass drums suck instead of blow (or vice versa!). The left and right channels can also be swapped over and muted individually, and there are buttons to switch in bass management and to mute a subwoofer, if the appropriate modules are included and configured (see ‘Cost Options’ box).
Two push-buttons directly above the encoder knob provide global Mute and Dim functions, the latter being adjustable and remembered separately for each monitor output. A new menu option, added at my request, remembers the mono and polarity settings associated with any output. This allows a single ‘mono check’ speaker to be connected to one output, with a summed mono signal being sent automatically whenever it is selected.
Output switching (with balanced and unbalanced modes) is provided for main, nearfield or mini loudspeakers, as well as headphones, and a powerful headphone amp is built in. Volume attenuation is controlled by the large rotary encoder in 1dB steps from 0 down to -50dB, with larger steps from there to -99dB. A ring of LEDs around the knob indicates the current setting in 3dB increments, and the precise output attenuation level is always shown in decibels in the LCD panel, alongside a ‘V’ (for volume) label.
Calibrated listening levels can be set up individually for each monitor output and, once set, the volume label on the monitoring LCD shows levels in dBr (relative decibels) rather than simply attenuation dB, with 0.00dBr being the set reference level. The actual monitoring level can be adjusted above or below this reference in the usual way (subject to the inherent attenuation range of the monitoring section), but with the benefit of an accurate display of the relative amount of volume adjustment. Essentially, this is the basis of Bob Katz’s ‘K-cal’ monitoring reference concept, where any volume-control adjustment away from the reference level becomes usefully representative of the comparative ‘loudness’ of the source.
Every monitoring source has an associated Trim, to allow different monitoring sources to be compared at similar perceived volume, with the current source’s trim value being displayed on the LCD alongside a ‘T’ (for trim) label. The available range can be set for ±5 or ±10dB (in 0.25dB increments), and the trim level for the current monitoring source is adjusted by pressing and holding the Opt-B button while turning the volume knob. The system works by introducing an offset to the selected monitoring level, rather than inserting some additional gain stage into the signal path, so it is entirely transparent and artifact-free. Trim levels are normally forgotten when the console is powered down, but they can be stored permanently if required. The Opt-A button, at the top of the monitoring panel, accesses the setup menus.
Source & Transfer Selector
The left-hand panel is just as logical as the monitoring panel, with the top eight push-buttons selecting the various monitor-path sources, and the bottom eight dealing with the transfer-path source and inserts. A Microsoft Word template is available if you want to print your own button labels. In addition to the two analogue and four digital monitoring-path inputs, there are four other monitoring options. These are the transfer-path source or output, and the analogue insert block’s D-A output or A-D input. These make checking and comparing the effect of any insert processing very fast and easy — especially since all of these monitoring selections’ volumes can be trimmed independently.
Selecting the transfer-path source, and the introduction of analogue and digital inserts, is controlled with the lower eight buttons. To avoid accidentally disturbing the transfer path, the Opt-C button must be pressed first, although it can be left permanently enabled if preferred. Assigning the transfer source requires it to be selected to the monitor path first, and then pressing the ‘Tfr Assign Src’ button routes it to the transfer path. Once assigned, the monitoring source can be changed as required without affecting the transfer path.
The insert points are configured in the same order that they are selected, with the only limitation being that the analogue inserts are always chained together in a block between the transfer A-D and D-A. However, within this group they can be placed in any desired order, and the block placed before, after, or in between any of the digital inserts (which can also be placed in any order).
Normally, if an insert is deselected and then reselected, it is added to the end of the chain. So if you program the inserts in the order 1,2,3, and then deselect and reintroduce insert 2, you’ll end up with 1,3,2. However, the order of the analogue inserts can be locked, if required, so that analogue processors can be switched in and out of the transfer path while always retaining their programmed positions in the signal flow. Strangely, this functionality isn’t currently available for the digital inserts, but it is a planned feature for a future firmware update.
Mysterious letters and numbers adorn the LCD at the top of the source-selection panel, but the manual quickly makes sense of them all. Across the top left-hand side, the letters C:O:S are shorthand for the transfer Converter, transfer Output, and Source assign. More letters below these tags indicate the corresponding sources. For example, the transfer Converter displays A or D depending on whether the analogue block’s A-D input or D-A output is being auditioned. The transfer Output display toggles between ‘S’ and ‘O’, representing either the transfer path Source or Output, while the transfer Source display indicates the selected transfer source: the two analogue inputs (A1, A2), or the four digital ones (D1 to D4).
The right-hand side of the LCD window logs the order of the inserts. The digital inserts are listed after the label ‘D’, while the analogue inserts are listed after the labels ‘A’ and ‘B’. The small letter ‘c’ appears within the digital insert list to indicate the location of the analogue insert block’s converters. This might seem complex, but it’s actually very logical: a display of D23c1 A21 means that the transfer source is routed via digital inserts 2 and 3 before being converted for analogue inserts 2 and 1. The transfer path concludes with digital insert 1. A little familiarity and experimentation quickly makes sense of it all, and it is very easy to use and understand in practice.
Since the transfer path is primarily digital, selecting an analogue signal as the transfer source inherently requires the use of the transfer A-D. The inevitable result is that any analogue inserts must be placed at the start of the transfer path too, before any digital inserts. This probably doesn’t matter in most cases, but an external A-D could be used to convert the analogue source to digital for presentation to one of the mastering console’s digital inputs, if a digital processor must be used before analogue processing.
Usefully, the analogue transfer path can also be split into two, called the A-path and B-path (hence the two insert labels mentioned above). This is a very handy feature in the larger consoles with a lot of analogue inserts available, catering for parallel-processing configurations. However, the last insert point’s send connection is redeployed as the B-path’s output, so in the little M1-3AI, parallel processing is restricted to using the first and second inserts with one in each path.
The Crookwood M1 is deliciously straightforward to configure and use, and the facilities are remarkably comprehensive and versatile. I can’t really tell you what the console sounds like, because it doesn’t have a recognisable sound at all! With analogue sources, it is utterly transparent, and I also failed to tell the difference between digital inputs routed through Crookwood’s own D-A and my Benchmark DAC-1, which is an impressive achievement. To test the complete A-D and D-A transfer path, I looped across the first analogue insert send and return sockets, and then switched the monitoring between the direct input source and the transfer-path output and, again, I really struggled to hear any degradation at all, with stereo imaging, transient attack, noise floor and bandwidth all remaining impressively consistent.
There is no doubt that this is a very high-quality mastering console, with excellent technical specifications and operational features. But it is also astonishingly cost-effective. The superb level of integration between the analogue and digital sources, monitor and transfer paths, makes mastering jobs much faster and easier to set up and work through. Auditioning and testing products is so much quicker and more repeatable, too. In fact, I’m now wondering how I coped before I installed it! If you are in the market for a cost-effective monitoring or mastering console, I can thoroughly recommend investigating the Crookwood options. I am very pleased indeed with my investment. 0
As the Crookwood mastering console is a modular system, various cost-options are available to expand its functionality. For example, there are three optional control-panel modules, one of which is a dual VU-meter panel with a control to adjust the 0VU reference level, while another is a simple talkback module. A very attractive option is a Trimmer/mixer panel to adjust the send and return levels of analogue inserts, or to combine and mix the returns from two parallel-processing paths. It also includes Mid/Sides encode/decode and stereo-width facilities. Optional internal signal processing cards include a bass management module, and additional A-D and D-A converters. The number of analogue and digital inputs, as well as the number of analogue and digital inserts, can also be expanded with extra interface cards, if required. There really are no limits.