Grace Design have brought their considerable expertise to the audio interface arena.
Grace Design are well known as purveyors of some of the very best microphone preamps and monitor controllers available, but there are more strings to the company’s bow, with highly regarded instrument preamplifiers, active DI boxes and microphone mounting systems in the portfolio — all brilliantly conceived and beautifully engineered, too. However, the latest addition to the family is a first for Grace Design: a sophisticated audio interface and A‑D/D‑A converter!
This new product, the m701, features a fully modular construction allowing the user to specify their own specific analogue and digital I/O requirements, with up to 64 channels of analogue conversion (in or out) and 212 digital channels in a wide variety of formats. The way that is arranged is through eight slots housing a mix of eight‑channel balanced analogue input and output cards (or four‑channel mic preamp cards), plus two slots for 32x32 digital cards (in AoIP, HDX or USB flavours), and a further option module currently used for 24 extra channels of AES3 — all this in addition to S/PDIF, ADAT and eight channels of AES3 I/O fitted in the unit as the base standard.
Although Grace Design have never offered a fully‑fledged interface before, digital conversion is certainly something of which the company have plenty of experience. After all, they have been incorporating high‑performance converters into their mic preamps and monitor controllers for 25 years or more, allowing Grace’s engineers to build up all the knowledge and skills needed to extract the very best technical performance from high‑end converters — expertise in analogue stages, power supplies, clock generation, grounding arrangements and much more, where small design tweaks have a big impact on the technical specifications.
Overview
The m701 is a 2U rackmounting unit with a typically understated grey chassis and front panel, dominated by a large (WVGA) colour display screen, a rotary data encoder, six menu navigation buttons, and an illuminated standby/on button. It is a simple, elegant user interface which belies the massive connectivity and signal routing potential hidden within. The standby button illuminates yellow in standby mode, green while booting, and white when operational.
Not surprisingly, the rear panel is a lot busier, being completely awash with connectors, many on interchangeable cards or modules to facilitate individual configuration requirements. Starting at the left‑hand side, a universal IEC mains inlet accepts 100‑240 V AC and has an integral mains on/off switch and fuse holder. Other connectivity fitted to the chassis as standard includes a single Ethernet RJ45 port (for network control via GraceNet — a browser‑based remote‑control app), and a USB‑A host socket for firmware updates or a Wi‑Fi access point connection. Additionally, standard digital audio I/O is provided on a pair of TOSlink optical sockets, an AES59 (25‑way D‑Sub) socket for eight channels of AES3, a pair of RCA phono sockets for coaxial S/PDIF, and a couple of 75Ω BNCs for word clock (with switchable termination on the input). The optical ports can be configured individually either for dual‑channel S/PDIF (operating at base and double sample rates) or ADAT, the latter carrying eight channels at base sample rates or four channels (using S/MUX) at double sample rates.
In contrast to the calm of the front panel, there’s a lot going on at the rear of the m701. The eight vertical slots (S1‑S8) can take any combination of eight‑channel line input (A‑D), eight‑channel line output (D‑A), or four‑channel mic input cards, to suit the user’s requirements. The two horizontal slots to the left of these take the high channel‑count digital I/O cards — any two from Dante, Ravenna, DigiLink or USB. Currently, the leftmost slot can be filled with 24 channels of AES3 (as shown) or left blank.
All other connectivity is configurable, starting over on the right‑hand side with eight vertical module slots, which can be fitted with any desired combination of eight‑channel balanced analogue line‑level inputs, eight‑channel balanced analogue line‑level outputs, or four‑channel mic/line modules, as mentioned earlier. All connections to the outside world are via AES59 (25‑way D‑Sub) sockets mounted on the individual modules.
The four‑channel mic cards use the same preamp design as found in the company’s superb m108 and m801 MkII preamps, and if two mic cards are installed alongside each other a ribbon cable links them so that all eight inputs are conveniently accessed through the first card’s AES59 connector. In situations requiring additional (or external) mic preamps, up to 12 external m108 microphone preamplifiers can be connected to the m701 over Dante, and fully controlled through the GraceNet user interface, with all settings stored within the m701’s memories.
A further two horizontal ‘Digital Interface’ slots on the rear panel each provide up to 32 more channels in and out. Compatible interface cards are currently available for Dante, Ravenna (and AES67) and Pro Tools DigiLink, and a USB 2.0 interface card should also be available by the time you read this review.
Any pair of interface cards can be installed, although the Ravenna card (which uses the Merging Audio ZMAN networking hardware) can only be used in slot 2. The Dante card employs the Brooklyn 3 networking hardware, and although it supports 32 channels in both directions at base and double sample rates, this reduces to 16 channels at quad sample rates. The Dante and Ravenna cards are both equipped with dual RJ45 sockets for primary and secondary network connections. For Pro Tools HDX/HD and HD‑Native users, the DigiLink interface effectively emulates two Avid HD I/O interfaces. Again the card is physically equipped with two sockets (Primary and Expansion), but only the Primary socket is currently enabled.
A third, much larger module slot accepts an optional panel carrying three more D‑Sub sockets for an additional 24 channels of AES3 in and out. As with the standard built‑in AES3 port, each of these eight‑channel interfaces can be configured individually for professional or consumer status data formats.
The m701 operates with a single clock domain, which means that all digital inputs must have the same sample rate and be synchronous with each other — ie. all clocked from the same master clock source. Anything that is not at the selected sample rate or correctly synchronised with it is automatically muted. There are no sample‑rate conversion facilities in the unit with the current firmware or, indeed, any kind of signal processing capability such as level adjustment, EQ, Mid‑Sides encode/decode — although the built‑in monitor mixer does have channel faders, so there is some DSP capability available within the FPGA. Perhaps Grace Design plan to expand the feature set in the future, but they have announced no plans so far.
Assuming the synchronous clocking requirements are met, any physical input can be routed to any number of physical outputs, configured using a simple cross‑point matrix graphical interface, with input sources arrayed on the left‑hand edge of the grid, and output destinations across the top. Channels can be routed individually by clicking on the appropriate cross points, or (by double‑clicking the Edit knob) as a complete block, with all source inputs within the selected interface module being mapped directly to their corresponding destination module outputs — a major time‑saver. Similarly, existing routings can be erased individually or across a complete block.
I mentioned the inclusion of a monitoring mixer just now, and there is a 32x8‑channel low‑latency mixer built in specifically to allow independent monitoring of any input or output. The control screen looks much like any standard DAW mixer, with familiar functions like mute and solo buttons, faders, pan knobs and input and output routing boxes (with eight groups). The eight monitor mix output busses can be used as individual mono sends or combined in odd‑even pairs to create stereo sends, and routed to any physical output. A really neat feature is that the m701 can generate a QR code on screen for each monitor mixer output, allowing mobile devices to connect over the network to the relevant channel very quickly and easily!
Naturally, each of the installed interface cards can be configured as required through dedicated menu pages. For example, on the analogue input and mic input cards, the converter’s anti‑alias filter characteristics can be selected from four different options: fast roll‑off linear or minimum phase, or slow roll‑off linear or minimum phase. Minimum‑phase selections have the least latency, of course (both are five samples), while the linear options are longer at seven samples for the slow roll‑off and 19 samples for the fast roll‑off.
The input sensitivity of the analogue line‑level input cards can also be switched for 0dBFS to equate with +18dBu or +24dBu (the EBU and SMPTE standard alignments, respectively). But there is also a ±20dB digital trim control (with 0.1dB increments) for meeting pretty much any system’s calibration requirements.
When mic modules are installed in the m701 additional configuration features become available, including phantom power on/off, polarity inversion, adjustable gain (+2 to +69 dB in 1dB steps, plus a ‑6dB setting), and a ribbon mode. This last option not only disables phantom power, but also increases the input impedance from 8kΩ to 20kΩ to improve the low‑frequency and transient response of ribbon mics. The ‑6dB sensitivity option allows the mic input to accommodate up to +30dBu, and the 20kΩ input impedance is sufficiently high for most line level devices, too.
The analogue line‑level output cards have the same reference alignment and digital trim options, but six different reconstruction filter modes. In addition to the linear‑ and minimum‑phase filters, and fast and slow roll‑off options, there are hybrid and apodizing filter modes, too. The minimum‑phase slow‑roll‑off filter has the lowest latency at just 3.5 samples, while the linear‑phase fast‑roll‑off and apodizing filters have the highest at 35 samples.
Apodizing filters are very clever because they remove the filter‑ringing artefacts inherited from any and all upstream conversion stages, while the hybrid filter is a halfway house between the linear‑ and minimum‑phase fast‑roll‑off filters: almost as steep as the linear‑phase filter, but with mostly post‑ringing and less latency.
Operations
Setting up and controlling the m701 is entirely logical and straightforward, even without consulting the well‑written user manual. I had no surprises when incorporating the review unit into my own studio.
Everything can be controlled directly from the front panel or, as the unit incorporates its own web server, via the GraceNet interface, which is accessible from any web browser. When connected to a local area network with DHCP, the web‑access address is shown in the lower right‑hand corner of the display in the form http://m701‑xxxx.local, where the ‘xxxx’ is part of the unit’s serial number. Entering this address into a web browser instantly accesses the unit remotely. (A static IP address can also be allocated, if preferred.)
The m701 can be controlled from its own screen, or remotely from a web browser (as shown here), with identical options and screen layouts. This Routing page shows the cross‑point matrix enabling any source (left edge) to be routed to any number of destinations (top). The green squares show confirmed routing cross points.
The unit’s menu system defaults to a home screen showing signal levels on vertical bar graphs (analogue I/O above digital I/O), with function tabs across the top and status data (sample rate, clock source and IP address) along the bottom. The navigation buttons or encoder knob allow different menu tabs to be highlighted — Inputs, Outputs, or (monitor) Mixer — and pushing the encoder then opens the selected tab. If viewed via GraceNet all inputs and outputs can be seen on the same screen, which is an advantage on a fully loaded system.
Configuring the unit is done via the Setup menu, accessed by pressing a navigation button to the right of the screen, marked with a cog symbol. This opens a dedicated menu with pages for Routing, Clock, I/O, Workflow, Display, Network, System, Status and Factory. A Back button exits the selected menu, and if any settings have been changed a dialogue appears to confirm or cancel the changes.
The functions of most of these menu pages is obvious: the Routing page displays the routing matrix as described earlier, and the Clock page selects the desired internal or external digital clock source. Options here include the two interface modules, AES3, optical port, S/PDIF, word clock or the three extra AES inputs (if that module is installed). There are also options for terminating the word clock input, and for selecting what the word clock output socket sends (either a loop‑through of whatever is connected to the word clock input, or the internal system’s clock). All standard sample rates from 44.1 to 192 kHz are supported.
On the I/O menu, specific configuration options are presented for the installed A‑D, D‑A or mic preamp cards, as well as the digital interface modules and the standard‑fit digital connections. There are settings for the converter filters, phantom power, gain, trim and reference levels, and so forth, all as mentioned earlier.
The Workflow page may sound unfamiliar, but it is essentially where all user settings and system configurations are loaded, stored, copied, named and imported or exported. Again, all very straightforward and logical. The Display page handles functions like the meter peak‑hold duration, the front‑panel normal and dim brightness levels, and the dim timeout duration — the display automatically dims a set time after the front panel controls were last used (between 10 minutes and an hour, or no dimming).
A Network page does exactly what you imagine it would, with options for setting DHCP or a static IP, gateway address, host name, and so on, while the System page accesses information including serial number, firmware revision, GraceNet version, system update options, debug logs, and digital interface card setup functions (for Dante and Ravenna network options etc). An internal SD memory card is used for storing logs and other user data, and there’s even a menu function to test the SD card’s health.
The Status menu provides information on the internal power rails, temperature of the main circuit board, and cooling fan speed, while the Factory menu — which requires a passcode to enter — is where the factory programs the unit’s serial number and FPGA, and it is not normally accessed by the user. The unit performs a self‑test on boot up and if it detects any changes to the hardware (eg. modules added or removed) it warns the user and automatically modifies the last used workflow to take into account any missing or new routing options and configurations.
Setting the unit up via the front panel display and controls is remarkably easy, but the size of the screen inevitably means there’s a fair bit of scrolling around — especially for routing. Using the GraceNet web interface generally allows all options to be seen at once (depending on the size of the computer screen), and I found I tended to use that more often than the front panel — although the meter screen was very useful for checking signal routings at a glance. Either way, the overall look and feel is very consistent between the two user interfaces and I had no trouble working with either.
Impressions
Grace Design’s new m701 feels much like their other products in the ways its menus are structured and settings configured. The range of I/O modules is impressive and, despite the huge I/O count, establishing connections between inputs and outputs is very straightforward and logical, as is saving and recalling different setups.
Having reviewed the Prism Sound Dream ADA‑128 in December 2023 I was naturally drawn to comparing the two units, which share broadly similar design goals, applications and I/O options. It’s fair to say that, in terms of quality and capability, the ADA‑128 has a substantially larger routing capacity, and its four independent clock domains make it far more versatile in complex multi‑room mastering situations — although that would be a very specialised requirement that most users of this kind of interface probably won’t require. Technically, the m701 slightly outperformed the Dream ADA‑128, which is very impressive indeed (see box).
It has surpassed even my expectations in terms of configurability, ease of use and technical performance.
When I heard the announcement of the m701 I thought it was a logical addition to the Grace Design portfolio, and it was bound to be an impressive performer. However, it has surpassed even my expectations in terms of configurability, ease of use and technical performance. This is one heck of a big‑boy’s interface!
Technical Performance
Entirely as expected, the technical specifications for the m701 are completely beyond reproach. For example, the mic preamp cards have an EIN figure of ‑127dB (150Ω source and 60dB gain) with a maximum input level of +30dBu (at the ‑6dB gain setting). Matching between channels is within 0.05dB and crosstalk is ‑122dB (at 10kHz). I also note that the A‑D input cards have a fixed high‑pass filter at 15Hz, whereas the D‑A output cards are DC‑coupled. And when it comes to saving the planet, the unit consumes a maximum of just 55 Watts, which is impressive considering what’s going on inside. It is fan‑cooled (at the right‑hand side), but it ran extremely quietly in the whole time I used it.
When it comes to the analogue I/O cards, at a 48kHz sample rate the overall latency from an analogue input to any digital output is just 0.2ms (with a minimum‑phase filter), rising to 0.5ms with a linear‑phase filter option. For any digital input to an analogue output the latency is the same with a minimum‑phase filter (0.2ms) but slightly longer with the linear‑phase options (0.8ms). Obviously, these times all halve with each doubling of sample rate.
I ran my usual AES17 dynamic range tests, achieving figures of 121.1dB (A‑weighted) for the A‑D card and 126.7dB (A‑weighted) for the D‑A card, which are superb results, both improving on the published specs, too (120dB and 125dB, both A‑weighted, respectively). These are exceptional results, ranking the m701 second in my table of measured D‑A converters and seventh in my table of measured A‑D converters. And at the top of these tables fractions of a decibel can dramatically change the rankings!
More impressively, the Grace Design m701 outperformed Prism Sound’s Dream ADA‑128, by over 2dB in both measurements, and sits comfortably between Merging Audio’s Hapi AoIP interface and the table‑topping Lynx Hilo 2. Confirming this sublime level of technical performance, the THD+N figures were equally impressive at 0.0002% and 0.00055% for the A‑D and D‑A cards, respectively.
Pricing
Modular Components
- m701 Base Unit £$3150.
- m701 8‑channel A‑D and D‑A cards £$895.
- m701 4‑channel mic preamp card £$895.
- m701 Dante or DigiLink card £$895.
- m701 24‑channel AES I/O card £$750.
- m701 USB 2.0 card £$695.
Factory Configurations
- m701 8x8 (DigiLink or Dante): Base Unit with eight channels A‑D, eight channels D‑A and DigiLink or Dante card, £$5543.
- m701 16x16 (DigiLink or Dante): Base Unit with 16 channels A‑D, 16 channels D‑A and DigiLink or Dante card, £$7244.
- m701 32x32 (DigiLink or Dante): Base Unit with 32 channels A‑D, 32 channels D‑A and DigiLink or Dante card, £$10,645.
- m701 Production (DigiLink or Dante): Base Unit with 16 channels A‑D, 16 channels D‑A, eight‑channel mic pre and DigiLink or Dante card, £$9134.
Prices include VAT.
Pros
- Comprehensive range of digital and analogue I/O options.
- Massively configurable.
- Typically elegant and practical user interface.
- Impressive versatility and technical performance.
Cons
- Mic input cards only accommodate four channels per slot.
Summary
The Grace Design m701 is a cleverly conceived high‑end interface/converter unit with a wide range of interfacing formats and a high channel‑count capability that makes it ideally suited to larger studio and mastering installations. Nicely engineered, and with excellent technical specifications, the m701 is an impressive product.
Information
See ‘Pricing’ box.
ASAP Europe +44 (0)20 8672 6618.
See Pricing box.
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