Allen & Heath GSR24

Firewire Analogue Mixer & DAW Controller

Published in SOS August 2011
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Reviews : Mixer

Achieving the perfect balance of analogue mixer and control surface in one product used to mean getting a mortgage on a high‑end SSL or reducing your analogue channel count. Not any more...

Hugh Robjohns

Allen & Heath GSR24

While Allen & Heath have, in recent years, concentrated their design and marketing efforts mostly on consoles and related products for live sound, the company have a strong pedigree in recording console design, with well‑regarded past products like the System 8, the Saber and especially the GS3000. The GS series has long been associated with serious recording mixers, whereas the company's more recent ZED series has been all about offering multi‑function professional features and build quality, but at an affordable price. The company have wanted to resurrect the GS line for quite a while — and they've been constantly asked to re‑make the GS3000 since it was taken out of production. With the all‑new GSR24 and GSR24M, the GS console is back — and what a comeback!

Overview

The success of the innovative ZED R16 recording console (reviewed in SOS November 2008), and the extensive user feedback gained from that product, are what encouraged Allen & Heath to expand the recording console line further. It's no surprise, then, that the new consoles are, in many ways, enhanced versions of the ZED R16: they combine an analogue console with an audio interface and comprehensive DAW controller.

In essence, the GSR24 is a 24‑channel analogue recording console, and installing an optional interface card brings integrated MIDI and DAW control facilities, and comprehensive interfacing and routing. There are currently two interface card options, one analogue and the other a Firewire/ADAT module. The latter can be used to interface and integrate a computer DAW very neatly and flexibly with the console. The desk also features an integral, full‑width meter‑bridge, and the channel and monitoring signal paths can be configured in a variety of ways (the manual lists nine distinct configurations) to enable direct multitrack recording or mixdown to and from a DAW, with latency‑free monitoring of live sources. Mixing can be performed using either the console's analogue mix buses (and EQ, if required), or 'in the box' using the console's MIDI‑capable channel faders to control the DAW.

The GSR24M is fitted with motorised channel faders, whereas the less expensive GSR24 has standard manual faders. Both versions can send MIDI data from the channel faders, although only the GSR24M's faders can respond to MIDI data from a DAW, and provide touch‑sensitive automation control. Given the additional hardware, the GSR24M is a couple of kilograms heavier than its sibling.

In addition to the 24 mono input channels, the desks also incorporate two valve‑based channels, to offer some added sound colour options, and four stereo line channels — so there are 34 inputs available for mixdown, or 38 if you also throw in the group insert returns. There are six aux buses, four groups, and independent stereo and mono main output buses. The monitoring is comprehensive too, with two independent studio cue outputs, and a 5.1 surround-sound control-room monitoring facility.

Integrated DAW‑control facilities include a comprehensive set of transport functions, two MIDI faders, 12 rotary knobs (these are conventional pots rather than endless data encoders) and 14 other configurable data buttons (including a set of navigation cursors) — plus, of course, the motorised channel faders in the GSR24M version and the manual MIDI channel and mono faders in the GSR24.

The overall construction and layout of the console is traditional, in the sense that each input channel is built on its own printed circuit board, suspended vertically below the conventionally arrayed channel controls, with input channels either side of a central (or rather, slightly offset) monitoring and control section, and a full meter bridge behind.

The mono-channel mic-preamp design employs the same topology as that used in the ZED R16 console (but not the other ZED-series mixers, which use a simpler design). The preamp is actually based on a derivation of a low-noise mix‑bus summing amplifier topology that was originally designed for a very expensive console back in the 1980s. It employs low-noise transistors and local feedback on each phase, to help achieve a very low noise performance (‑128.5 EIN at 60dB gain) and exceptionally low distortion. It's a lovely, transparent preamplifier that receives a lot of plaudits.

The EQ section is also the same as on the ZED R16, having twin parametric mid‑range sections with extended frequency ranges. The bus summing circuitry on the main mix also uses low‑noise transistors to minimise the noise floor and maximise performance during analogue mixdown. All of this adds up to make the GSR24 a quality mixing console.

Console Inputs

As well as the usual array of group channels and aux controls, the master section includes transport controls for your DAW, and two valve channels, which allow you to dial in some sonic colour.As well as the usual array of group channels and aux controls, the master section includes transport controls for your DAW, and two valve channels, which allow you to dial in some sonic colour.

The basic signal path through the console, and the main channel facilities, are all pretty straightforward and familiar. The complexity comes from the numerous ways in which the interface module's I/O can be involved in the signal path, and the MIDI configuration options.

The 24 mono channels are arranged with 16 to the left of the centre section, and eight to the right. They are all equipped with balanced microphone and line inputs, both feeding the same preamp stage via a push-button selector at the top of the channel strip, sitting alongside the usual facilities of phantom power, polarity inversion and high-pass filter (12dB/octave from 100Hz). There is no mic pad, but the preamp will accept signals up to +14dBu before clipping, and has a gain range of +6 to +60dB in mic mode (and ‑14 to +40dB in line mode). The circuitry is derived from that employed with great success in the ZED R16. The console specifications claim the preamp section has a wide bandwidth (20Hz to 80kHz ±1dB at 50dB gain), very low distortion (0.0035 percent) and a good noise performance (‑128.5dBu at 60dB gain, falling to ‑124dBu at 30dB gain).

An impedance‑balanced direct output is provided on each channel, with the output source being determined by internal jumpers. Four options are available, two post EQ (before or after the interface-signal inject point selection — see below), and two post-fader, before or after the fader‑bypass switch. These options allow the direct output to carry the unadulterated preamp output, or to follow the preamp/interface source selection, and to be affected by, or remain independent of, the channel fader, including when the console faders are used as MIDI controllers. So there's lots of flexibility there.

An unbalanced insert point precedes the four‑band EQ section, which is surrounded by the interface module I/O routing switches. The direct signal to the interface card (the A‑D converter in the case of the FW/ADAT card) can be taken either from the high‑pass filter (straight after the preamp section), or after the EQ section, as determined by a button labelled, unhelpfully 'A', placed in a group of four, each with associated status LEDs at the bottom of the channel strip.

The return signal from the interface (the D‑A converter in the FW/ADAT card) can be routed, using button 'B', either to the input of the EQ section (just before the insert point, and replacing the output from the preamp section), or to replace the output from the EQ section with button 'C'.

These three lettered routing selectors allow the desk to be configured very flexibly (there are eight possible configurations!), including as an in‑line console (routing the preamp input to the DAW and the DAW return back through the channel path). The EQ section can be allocated to either the record or the replay path, and the DAW replay signal can be routed through the insert point and EQ section, to be recorded straight back into the DAW for mixdowns and overdubs, if required. All in all, it's a superbly flexible arrangement — although the panel markings are not even slightly intuitive, and the lettered buttons are meaningless until you've read and memorised the manual!

The mono-channel EQ section is well specified, with fixed shelf sections top and bottom (providing ±15dB gain at 12kHz and 80Hz, respectively), and two fully parametric mid-range sections. The latter provide the same ±15dB gain range, with Q (bandwidth) controls spanning a broad 0.8 (almost two octaves) to a narrow 6 (a quarter octave). The upper section can be tuned from 400Hz to 18kHz, while the lower spans a nicely overlapping 18Hz to 1kHz. An overall EQ in‑out button is provided, complete with a status LED.

Returning to the signal path, after the interface/EQ selector button 'C', the signal is distributed to the pre‑fade channel metering (a 12‑segment, peak‑reading LED bar-graph), the PFL monitoring bus, the pre‑fade aux sends and the channel mute button, which then feeds the channel fader. The fader can be bypassed at unity gain using the last of the four buttons above the fader (button 'D'), to allow the console to be used as a unity‑gain analogue mixing system, while the fader is employed to control the DAW source channels via MIDI.

The output from the fader feeds the mono mix-bus and, via the pan‑pot, the four groups (in pairs), the main stereo bus, and the AFL monitoring bus. The bus routing is performed via four more push buttons, which are placed between the channel pan control and the four routing configuration buttons. The illuminated channel-mute button sits below the routing buttons, and the Solo/Select button (also illuminated) between that and the fader. The channel solo mode can be switched globally from the centre section between PFL, stereo AFL, and solo‑in‑place modes, and it can also be used to send MIDI messages for functions like DAW channel select, mute or record arm.

The 100mm fader controls the channel audio signal level (unless in fader bypass mode — button 'D'), but can also be used to send MIDI parameter data to a DAW, as already mentioned.

The channel's six aux-send rotary controls are fed in pairs, with the first two permanently pre‑fade, the middle two switchable pre/post, and the last two normally fixed post‑fade. All six can be used simultaneously, and the pre‑fade point can be configured with internal jumper links to be pre or post the channel-mute button. Auxes 5/6 can also be reconfigured as fixed pre‑fader sends if required. Unity gain is marked at the three o'clock position on the rotary controls, and there's an additional 6dB of gain available.

The MIDI control parameters from the channel faders and solo/select buttons, the 12 centre‑section knobs and two MIDI faders, the transport controls and assignable buttons, the cursor buttons, and the jog wheel, can all be configured in various ways. The default mode is a unique MIDI mapping (fully documented in the handbook) specific to the GSR24, but there are also emulation modes to mimic the Tascam US2400 control surface or a generic Mackie HUI protocol, which a lot of DAWs already recognise. There are also options for setting the button tally lights to respond to internal or external control.

Additional Inputs

Each of the mono channel strips features switchable EQ, including two fully parametric bands.Each of the mono channel strips features switchable EQ, including two fully parametric bands.

Extending the 24 mono channels, the desk also has four stereo input channels, located between mono channel 16 and the centre section. Inputs 1 and 3 are connected via unbalanced RCA/phono sockets, whereas inputs 2 and 4 are on balanced quarter‑inch TRS sockets. Although inputs 1 and 2 share one channel strip and inputs 3 and 4 share the second, the facilities afforded each input are rather different.

The odd numbered (RCA/phono) inputs are normally routed straight to the main stereo mix bus and nowhere else. There are no other facilities: there's no metering, and there's not even a PFL button to check the incoming source. However, a 'below the surface' button can be pressed to re‑route the input through the main stereo channel path, mixed with the even numbered input.

The even‑numbered inputs (which are presented on balanced TRS sockets) are routed through a conventional stereo channel strip, with a four‑band EQ section (complete with a bypass button, but no insert socket), all six aux sends, full mono, group and stereo bus routing, mute and solo/select buttons, and 100mm faders. A bar-graph meter in the bridge displays a pre‑fade mono sum of the stereo channel, and a 'SIP‑safe' button disables the automatic channel muting that would normally be activated when another channel is soloed. This is really handy if the channel is used as an effects return, since the effect will remain audible when other channels are soloed.

The stereo channel equaliser is slightly simpler than that on the mono channels, with the same top and bottom shelf sections, but with two fixed-frequency mid sections (centred at 250Hz and 2.5kHz). All four stereo inputs have independent level controls with 10dB of gain in hand.

The interface module I/O routing arrangements in the stereo channels are similar to the mono channels, with buttons to derive the send to the interface from either the input buffer or the EQ output, and to route the return to the input of the EQ section, replacing the input source. Essentially, these buttons do a similar job to the mono-channel 'A' and 'B' buttons, although here they are given much more meaningful panel labels (Send = post EQ and I/P = DAW)! The 'C' and 'D' options of the mono channels are absent in the stereo channels — the DAW return can only be routed via the EQ section and not directly to the bus routing, and there is no fader bypass mode.

Taking The Tube

In case 24 mono channels and four stereo channels aren't quite enough for you, there are also two 'valve input' channels, which are located just above the group channel faders. The two mono valve channels accept either balanced mic (on XLR) or unbalanced instrument/line (quarter-inch TS jack) inputs, with the latter being routed through a FET gain stage, which provides a very high (10MΩ) input impedance. Phantom power is available for the mic input, and a polarity-inversion button is also provided, along with an instrument 'boost' button, which raises the FET‑stage gain by 26dB. This can be used to accommodate low-level guitar pickups, or as a way of driving the valve stage harder. As with the main mono channels, a rotary gain control provides +6 to +60dB in mic mode, and ‑14 to +40dB in instrument/line mode — the latter being increased if the gain boost button is pressed, of course. A fifth push button replaces the input circuitry (post gain control) with the corresponding channel from the interface module, allowing DAW channels to be processed via the valve stage if required.

The valve amp operates in parallel with a solid-state path, and a rotary 'drive' control, with a large vintage‑styled knob, balances the outputs of the two in a kind of 'wet‑dry' format. At the minimum setting, the signal is taken entirely from the solid‑state path and is very clean, while at the maximum setting it is taken entirely from the valve stage, and is 'harmonically enhanced'. Intermediate positions allow a broad range of sound character from subtle to obviously 'grunged'. A three‑colour LED indicates how hard the valve stage is being driven, and this is determined by the input level, which can be set using the channel gain control or the DAW's output level. Two valves glow gently through a slotted vent on the panel.

After the drive blend control, the signal path flows via an unbalanced insert point to the channel metering and a rotary level control (in lieu of a fader) for distribution to a balanced direct output, the corresponding interface send, mono bus routing, and a stereo pan pot, which in turn feeds the routing to the group pairs and stereo bus. There is an AFL monitor button but no PFL and, more significantly, no access to any of the aux sends. I found this rather frustrating, since it makes it impossible to add some 'comfort' reverb for cue monitoring, for example, and during my time with the console I often ended up patching the direct outputs externally back to a couple of mono channels just to access outboard effects easily. I imagine the absence of aux facilities is due to panel-space limitations, but it does seem like a poor compromise to me, and I'd have preferred a smaller drive knob to leave more space for an aux level control, and maybe a button or two to select which aux send!

That completes the mixable input side of the console, although there's one other input source: the built‑in talkback microphone. This has a gain control and a 'talk' button, with independent routing switches for the studio monitor cue feeds, auxes 1/2 and 3/4, and all four groups (simultaneously).

Console Outputs

The rear panel of the GSR24 — with more holes than Blackburn, Lancashire!The rear panel of the GSR24 — with more holes than Blackburn, Lancashire!

The output side of the desk is almost as versatile as the input side. The four mono groups' signal paths each include an unbalanced insert point and a non‑motorised group fader, followed by an AFL button, mute switch, group metering (a small four‑LED bargraph set into the fader panel, rather than in the meter bridge), and routing to the mono and stereo mix buses (the latter via a pan‑pot, of course). There is also a balanced TRS direct output socket.

By default, the group outputs are not accessible from the interface card, but there's a 'below‑the‑surface' button to the right of the monitor section which replaces the interface sends from channels 17‑24 with the first four aux sends and all four groups, allowing submixes to be recorded or processed externally.

The master mono mix bus has a similar structure, with an unbalanced insert point, fader, and a balanced TRS jack output socket. On the GSR24 version of the desk only, the mono master fader can be bypassed. This provides a unity-gain output, and allows the non-motorised fader to operate as a MIDI data fader instead. (This feature does not appear on the GSR24M.)

The master stereo mix bus output routing is, as you might expect, slightly more elaborate. The stereo mix bus amps collect signals from the 24 mono channels, four stereo channels, two valve channels, and the stereo 'digital master' return from the interface module (via its own level control, which is located at the bottom of the monitoring section). The signal path then flows through unbalanced inserts to the separate left and right main faders, and on to the moving‑coil VU metering, the appropriate interface sends, and the stereo mix balanced outputs (on XLRs).

Another push button replaces the stereo mix bus with the return from an external stereo recorder (labelled 'two track 1'), and two more buttons allow direct dubbing both ways between 'two‑track 1' and 'two track 2' — the latter being connected via unbalanced RCA phono sockets, and the former via balanced TRS sockets for the returns and the main output XLRs for the sends).

The six aux-send masters are arranged above the group faders, and are equipped with individual rotary level controls and AFL buttons, driving impedance-balanced outputs on TRS sockets.

Monitoring

The monitoring facilities are fairly comprehensive, comprising two fully independent studio or artist (cue) monitor sections and a separate control-room section. The two stereo studio monitor sections each have eight rotary level controls, which allow a cue mix to be constructed from a variety of sources. Up to four aux buses can be accessed simultaneously (there are dedicated level controls for auxes 1 and 2, and two more controls switchable between auxes 3/4 or 5/6), along with all four groups, and both the stereo and mono buses. The groups and stereo buses can also be switched between mono or stereo. Rotary master level controls are provided, along with AFL buttons, so the cue mix can be auditioned in the control room, and the outputs are provided via more impedance‑balanced quarter-inch TRS sockets.

The control-room monitoring defaults to auditioning the main stereo mix bus, but four push buttons enable monitoring of the mono mix bus, the master return from the interface module, or either of the two‑track inputs. The AFL and PFL buses, when activated on a channel, override the selected monitoring source, with an illuminated 'solo clear' button, to warn when solo is active and to clear any unwanted solo selections.

A mono button sums the left and right control-room monitor channels together before the metering and output routing facilities, and a pair of 12-segment LED bar-graph meters is provided at the top of the monitor section to display the monitored signals. A single headphone level control is provided, but there are two output sockets (one on the front panel and the second on the rear).

The monitor signal path continues to the speaker distribution, which includes a 20dB 'dim' button and an 'alt' speaker selector, to swap the monitoring signal between the main control room and alternate speaker outputs (all are impedance balanced and on TRS sockets). A rotary volume control sets the level for all of the control room monitor outputs, so level matching between main and alternate speakers has to be done on the monitors themselves (or their amps).

Another below‑the‑surface button (alongside the one I mentioned earlier to select channels 17‑24 or the auxes and groups to feed the interface module), switches the control‑room monitoring into a 5.1 mode. In this configuration, return channels 25‑30 from the interface module are routed directly to the control‑room outputs via the volume control. This mode overrides the normal stereo monitoring source selection, although PFL and AFL signals are allowed through to the selected main or alt speakers. The main control-room speakers are assumed to handle the front left and right channels, while the alternate speakers carry the left and right surrounds. Two extra quarter-inch TRS jack sockets are provided for the centre and LFE channels, and are only active when working in the 5.1 mode. There's no provision in the console for any form of bass management to redirect low‑frequency signals from the main channels to the subwoofer if small speakers are being used.

The talkback facilities are near the top of the monitor section, with a flush‑mounted electret microphone positioned above a non‑latching 'talk' button, which I found rather anonymous in the middle of the centre-section controls. The talkback destination is selected with four more push buttons, routing the signal to the studio monitor outputs, auxes 1 and 2 (as a pair), auxes 3 and 4 (as another pair), and to all four groups (en masse).

Finally, as far as the audio paths are concerned, three more push buttons (all with LED indicators) above the stereo mix faders select the channel solo auditioning modes. There are five options: (mono) PFL, (stereo) AFL, (stereo) Solo‑in‑Place (SIP), Add mode, and Select mode. The first three are obvious; Add mode allows multiple channels to be soloed simultaneously, instead of each new selection cancelling the previous one, and Select mode disables the solo function, so that the channel-solo buttons can be used to send MIDI data to control the channel's select, mute or record-arm functions in a DAW.

A pair of MIDI fader mode buttons performs different functions depending on the console version. In the GSR24M, with touch‑sensitive motorised faders, the buttons switch between channel-fader read and write modes. In the GSR24 console, one button enables the sending of MIDI data from the console's manual channel faders, and the other bypasses the mono master fader's audio path and enables it to send MIDI data instead.

DAW Control

The A&H web site has several detailed setup documents to help configure the GSR24 with different DAW platforms, including Cubase, Logic, Pro Tools, Reaper, and Sonar — although the general principles can be extended to work with other platforms quite easily. The first critical element involves setting up the DAW to use the console as its audio interface (using either ASIO drivers or Core Audio, for PCs and Macs, respectively), and allocating the channels appropriately. The MIDI data to and from the console can be mapped, learned or translated by the DAW program, and there are various console configuration modes (see above) to help with this. To use the MIDI via Firewire option, the appropriate driver must also be installed, after which 'A&H Firewire' appears as a MIDI device in the host computer.

Many DAWs already recognise the HUI protocol, and I configured the console in this mode, using Bome's MIDI Translator to link the DAW's (SADiE) HUI interface and the console's MIDI data (templates are available on the A&H web site for Pro Tools, Reaper and Sonar). When configured, the console's 24 channel faders are mapped to the first 24 tracks of the DAW, the PFL/Sel buttons activate the DAW track solos, and the transport buttons control... erm... the transport functions! The (non‑continuous) rotary encoders and assignable buttons can be used to control plug‑ins, although this generally relies on the DAW having a MIDI learn or assign function, so that specific controls can be mapped to specific functions. It's an approach that's a little restrictive, perhaps, but it works well enough, given some programming effort.

For Logic users, it's easiest to use the US2400 emulation mode, since a suitable plug‑in is already available, and for Cubase users the Default MIDI mode is recommended — although this involves 'teaching' the DAW the various MIDI functions, which is a bit more long‑winded than using the emulation modes. However, once configured appropriately, the whole thing works efficiently and reliably.

Conclusion

The GSR24 is a lovely desk that takes the excellent sonics and operating concepts of the ZED R16 and expands upon them to make an even more powerful and better integrated studio console/workstation. Even before you consider the DAW-control features, the flexibility of the routing make this desk something special: the ability to choose where in the channel strip the recording sources are derived from, and where the DAW replay signals are fed back in, provides a great deal of versatility, making both recording and mixing very flexible and creative. I particularly liked the ability to record and/or replay through the channel EQs, and to be able to choose whether to mix with analogue signals from the DAW, or to mix in the box and use the console purely for summing and control.

The main channel mic preamps sound nicely clean and open, although the gain control knob does get a little congested at the top end. The EQ section is excellently judged, and works equally well for gentle sound sculpting and aggressive tonal correction, with a beautifully smooth and musical quality.

The large number of accessible auxiliaries and the comprehensive cue-monitoring sections make the job of building artist mixes and effects chains straightforward, and including a facility to accommodate basic surround-sound monitoring in the control is another thoughtful feature. The lack of access to aux sends from the valve channels is a minor frustration, but the inclusion of the valve channels is a definite bonus, and it's easy enough to patch their direct outputs into spare channel inserts.

A couple of negative issues were highlighted in the SOS review of the ZED R16 console, one being that the stereo channels couldn't be routed to the interface, and the other that there was no solo‑in‑place facility. Clearly, the designers at A&H took note, because both issues have been addressed in the GSR24 consoles.

The GSR24 is a fabulous mixer in its own right, and the analogue interface card option makes it a supremely versatile studio centrepiece, even for 'traditionalists' who want to work with tape or hardware digital recorders in the old‑school way. However, for 'modernists' wanting to integrate their DAW and console, the GSR24M does precisely that in a way that's both elegant and flexible. The non‑motorised version of the desk integrates almost as well, of course, but for me moving faders are essential in this environment and they certainly work well in this instance. With the Firewire card, the GSR24M lists at a shade under £7000 plus VAT in the UK, and while that's a serious chunk of money, you're getting extremely good value for it. If you're looking for a new console, there may be more upmarket options available, but none of them provides the same level of interface integration, and few offer more in terms of routing flexibility or significantly better sonics. Highly recommended!   .

Alternatives

The concept of integrating an analogue console with DAW-control facilities has become a very popular one, and many manufacturers now offer variations on the theme, such as the Audient Zen and ASP2802 (now the Focusrite Control 2802), the SSL Duality, AWS 924/948, Matrix and Nucleus, and several others — not least A&H's own ZED R16, of course.

Interface Cards

The analogue interface card provides MIDI In and Out, plus 32 inputs and 32 outputs on two big 37‑pin D‑sub connectors. Obviously, bespoke break‑out cables are required, and the input and output connections are all unbalanced. The second card, which was fitted in the review model, is the Firewire (FW) interface, which provides MIDI In and Out again, plus 32 channels of ADAT digital audio in and out (via four Toslink ports in each direction), along with a word clock in and out on BNC sockets, and two FW400 ports. DIP switches configure the interface to operate as FW only, or to use a combination of FW and ADAT, and to determine the sample rate and clocking modes. The FW‑only configuration supports base and double sample rates, while the ADAT modes support only the base rates of 44.1 and 48kHz.

The FW/ADAT module is supplied with both 6‑6 and 6‑4 pin FW400 cables, and the control data can be routed either via the conventional MIDI ports, or embedded within the FW interface. There are two FW connectors, and a ZED R16 console can be cascaded with the GS R24 if required, by using the second FW port.

The analogue‑digital converters in the interface module are configured with a fixed headroom alignment of 0dBFS = +18dBu (the console itself clips at +23dBu). The module passes 32 channels assigned as mono channels 1‑24 (17‑24 can be reallocated to Auxes 1‑4 and Groups 1‑4 if required) to interface channels 1‑24, stereo channels 1 and 2 to interface channels 25‑28, the two valve channels to interface channels 29‑30, and the main stereo mix to interface channels 1‑32.

Firewire Control Software

Allen & Heath GSR24

The DAW control‑surface elements of the console only become accessible if one of the interface modules is installed, as these carry the MIDI In and Out sockets. Although the review console was supplied with both the analogue and the Firewire (FW) modules, I spent the majority of time using the FW/ADAT card, as this is the option that is likely to appeal to users who want to integrate the console with their existing DAW system — which is probably the larger part of the potential market for this desk. With this card installed, the MIDI data can also be accessed directly via the FW interface.

Drivers are required to allow a host computer to communicate properly via FW with the consoles, and the latest versions can be downloaded from the A&H website (v3.5.5 at the time of writing). I ran the system quite happily on a PC laptop for the review, but Mac drivers are also available.

The FW 'audio streaming' device control panel has two main sections, labelled 'Global Settings' and 'Device Settings'. There are a few minor differences between the PC and Mac versions, related to the operation of the two platforms. In the Global Settings section, the PC version has five tab buttons (Bus, WDM, DPC, System and Info), whereas the Mac version has only two (Bus and Info). Both versions have drop‑down options for selecting the master device (GSR24), sample rate, sync source (ADAT, word clock or internal), buffer size and operating mode. Seven buffer-size options are offered, ranging from 64 to 3072 samples, and the four operating mode options are normal, and safe mode levels 1‑3, although some of these modes also restrict the buffer size options too. Basically, the safe mode levels offer progressively more security against performance related dropouts, in part by increasing the buffer sizes.

In the PC version, the WDM tab button allows Windows WDM audio channels to be mapped to the GSR24 channels, if required, while the DPC tab button accesses a latency checker function — not of the audio latency, but of the deferred procedure call (DPC) delays within the computer, which can affect the integrity of audio streaming in and out of the PC. Once the checker has assessed the DPC delays, the recommended operating mode is displayed. The DPC delay depends on a wide variety of functions that require the computer processor's attention, such as network connections, peripherals connected to USB or FW buses, heavy video graphics processing and other running applications. By running the DPC checker when the DAW system is running along with all the connected peripherals (like external drives), an accurate reading can be obtained and the buffer sizes optimised for reliable operation. The last PC‑only tab is labelled 'System', and this is another automated checking function that evaluates the host computer chip set and then advises of any compatibility issues (or required updates) with the DICE FW streaming hardware that Allen & Heath use in their consoles.

The Device Settings section of the FW panel shows the connected device(s) and their clock status, while the first (General) of two more tab buttons accesses a device description page, which allows a user‑specific label to be added to identify the connected devices if there are more than one. The firmware loader button allows updated firmware to be installed in the FW interface card in the console.

Allen & Heath GSR24
pros
Great‑sounding preamps, EQ sections and analogue summing.
Valve channels for 'character' sources.
High channel‑count for mixdowns.
Very flexible artist cue mix facilities.
Rudimentary but useful surround‑sound monitoring facility.
Effective and fairly comprehensive MIDI control facilities.
cons
No aux send access from the valve channels.
No ability to PFL or meter the stereo inputs.
No bass management facilities in 5.1 mode.
summary
This large‑format, high‑quality analogue mixing desk boasts a comprehensive feature set, both as a console and as a combined interface and DAW controller. It builds strongly on the success of the ZED R16, addressing the weaknesses of that console and developing the theme further, with even better integration and flexibility.
information
GSR24 £5999.99; GSR24M £6719.99; analogue interface card £220.80; Firewire interface card £640; RPS15 power supply £960. Prices include VAT.
Allen & Heath +44 (0)1326 372070.
GSR24 $10,999; GSR24M $11,999; analogue interface card $299; Firewire interface card $799; Rps15 power supply $1,599.
American Music & Sound +1 800 431 2609.

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