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Allen & Heath S2

Recording Mixer

Article from Sound On Sound, September 1991

Not content with offering most of the Saber's facilities in the highly affordable Spectrum, Allen & Heath have now produced in the S2 an even cheaper fully-featured recording console. Dave Lockwood tries it on for size.

Allen and Heath's last budget recording desk, the Spectrum, understandably caused quite a stir when it was launched. It seemed to provide most of the important facilities of its up-market companion, the Saber, at an outrageously low price. This line of development is taken a stage further with the company's new S2 model, which is even more attractively priced than the Spectrum, and yet shares many of its essential features and performance standards.

Although the styling and finish are characteristically Allen & Heath, construction and indeed concept seem to owe more than a little to Soundcraft's excellent Spirit console. The principal criticisms one could level at the Spirit are the absence of a MIDI muting system and the lack of expandability. The S2 has both. With no obvious omission to set against its plus points, it already looks like strong competition for the Spirit.

The basic S2 configuration is a non-modular 16-8-2 in-line console, which can be expanded with up to two further blocks of eight input channels. When these are added, the distinctive aluminium extrusions which form the front and rear edges of the unit are replaced with new full-length pieces, providing good structural integrity and rigidity in the enlarged desk, and minimising the 'DIY-look' typically characteristic of expanded systems.

The in-line monitors of the S2 have sufficient facilities to be taken seriously as additional channels on mixdown, and four stereo F/X returns are also included, so the 16-input console actually offers 40 inputs with EQ, whilst the fully expanded 32-input unit offers a remarkable 72 (32 inputs, plus 32 monitors, plus 4 stereo returns)!

All connectors are located at the top of the control surface, which is formed from a single piece of dark grey-finished steel. Whilst this is principally an efficient and economical means of manufacture, it does also have its operational advantages. Apart from the space-saving effect of being able to place the unit right up against a wall, having all the connectors within easy view and reach creates a virtual patchbay for users not yet ready to invest in the real thing.

The only drawback to this system is that, unless you use decent quality, properly loomed cabling and connectors, you can finish up looking at an absolute mess in which the prospect of repatching anything is distinctly uninviting. It is unfortunate that, whenever the top-mounted connector system is used (the Spirit is the same) the insert points seem to be located in the middle of the array instead of in the most accessible position, on the outside, nearest to the operator. Surely these are the connections most likely to change in the course of normal operation? Most small system operators I know try to run their MIDI set-ups with instruments permanently patched to specific inputs, but nobody uses the same inserts all the time.

With an S2 connector panel fully loomed you will have a wall of XLRs followed by a secondary layer of jacks to get through before you can get at the inserts. Yes, of course you would be better off using a patchbay, but not everybody wants to, or can afford to, and nor would they have to with a little more thought in this area.

All connectors on the S2 are unbalanced 1/4" jacks, with the exception of the electronically balanced XLRs used for the microphone circuits. Inserts are via the standard tip-send, ring-return, stereo jack system. The extremely compact, free-standing external power supply connects to the desk via a multipin XLR, with fixed cables (approx. 1.5m) used for both mains input and PSU output. Easily accessible individual switching is provided on each mic input for the 48V phantom supply.

Input to the channel path is via the Mic/Line selector switch, operating in conjunction with the channel gain control. An input Reverse facility is available to swap the line input to the channel with the tape-return input which normally feeds the monitor. The gain control is active on the tape signal when that is the source assigned to the channel path. The 56dB gain range of the mic/line amp will be quite sufficient for normal operation, but the absence of a pad facility could conceivably cause some difficulty if a high-output condensor mic were to be used for close-miking a loud source.


Following the signal path rather than the physical layout of the channel (the monitor facilities actually occupy the space immediately beneath the input controls), we arrive next at the auxiliaries. Four sends are provided, all postfade, fed from two pairs of dual-concentric controls. In addition, there is a dedicated Cue mix bus; although the final Cue mix output is stereo, the individual channel sends are mono, so the actual foldback mix will only be stereo if the Cue mix switching is selected to a stereo source, such as the mix bus.

Auxiliaries 1 and 2 can be switched, as a pair, to operate from the monitor path rather than the channel signal. Shared facilities are always a compromise, but a necessary one to make the most efficient use of the available control space. Two post-fade sends are perhaps the minimum you can expect to get away with for any serious work. The problem that usually arises when monitors are treated as extra inputs is that you will probably want both monitors and channels to be able to access the same two primary effects. One solution to this is to utilise the separate left and right inputs on most F/X devices, feeding one side with an aux from the monitor pair, and the other side with an aux from the channel pair. With very few exceptions, such 'stereo' input devices invariably merely sum the two inputs together to create the feed to the processing stage.

Monitor channels also have a dedicated Cue send, although this feeds an entirely separate bus from the channel Cue. The obvious omission in the facilities of the S2 is the absence of a pre/post-fade switch for the cue sends — that would have given potentially three post-fade sends common to both signal paths (via paralleling); a considerably more usable arrangement than many compact desks.

As it is, you can still get away with using pre-fade sends for effects; you just have to remember to also alter the send whenever you alter the channel level. The Cue send's failure to follow the mute status however, is probably a limitation of greater practical significance.


The S2 main channel equaliser consists of two quasi-parametric, 'sweep', stages, with a fixed-frequency, shelving HF control. The latter provides 14dB of cut or boost at, according the front-panel legending, 16kHz. Subjectively, it doesn't seem to sound quite as high as 16kHz, but it is nevertheless, in my opinion, too high. There are few natural sources that could be genuinely enhanced by boosting at that sort of frequency, whilst with many electronic sources there is often nothing at all up there apart from noise. In a limited system such as this, I would much prefer to have the fixed HF at around 12kHz.

The fact that the sweep mid control goes to 12kHz does not mean it can do the same job. The mid and LF controls have a peaking/notching characteristic, providing an action centred on the nominal frequency. A shelving filter boosts by the specified amount at the nominal frequency and at all frequencies above (or below in the case of a shelving LF), within the limits of the overall system response. A 12kHz peak is a very different effect to a 12kHz shelf.

Both dual-concentric lower EQ sections provide the same +/-14dB, covering the ranges 300Hz to 12kHz for the mid, and 15Hz to 600Hz for the LF stage. Nobody's ever going to complain about having too much range on an EQ stage, but I doubt if there is going to be much of real interest going on at 15Hz. If we assume that a bass-drum fundamental would be somewhere around 60Hz, 15Hz is a whole two octaves below that! 30Hz would probably be a more practical cut-off point, and would also not have wasted resolution in that area of the pot. Personally, I would also have preferred a few more frequency markings around the EQ controls.

In use, the EQ is controllable and has a fairly precisely predictable effect. The preset bandwidth of the sweep filters has been fixed at a good compromise value for both creative work and 'notching-out' troublesome frequencies. This is an efficient little EQ for a compact budget desk, of limited scope for precision work (no 'Q' controls, no choice of frequency at HF), but nonetheless capable of respectable audible results. Despite my reservations regarding the frequency bands, I found I could generally get somewhere near to what I wanted out of it, particularly with electronic sources.

EQ in/out switching is provided, but the individual band-gain controls are also centre-detented; a definite plus-point in my book, letting you know for certain that bands that you do not want to affect are at their nominal flat points.

A red LED Peak indicator is provided, indicating clipping within the channel. The detection point is post-EQ, so equaliser-generated overload will be detected, but input amplifier clipping may not if the net effect through the EQ is a reduction in level. A standard PFL circuit is provided for monitoring signals in isolation (PFL is non-destructive, ie. it affects neither group nor Left/Right busses, only the monitor output) and can therefore be safely activated during recording or mixing.

A momentary-switched electronic mute element is included, which can be operated both manually and under the control of the on-board MIDI Mute Processor. As on all the consoles that feature this muting system, mute operation is remarkably silent and free of audible vices when interrupting the signal, suggesting that muting is probably ramped.

Mute activation kills the entire channel, with the one exception of the cue send. I cannot see the point of this. If you need foldback from a channel that you don't want in the mix, the send is pre-fade anyway; you can achieve this simply by leaving the fader down. If the cue send is pressed into service as an additional F/X bus, you certainly would not want it to remain active when the channel was muted.

Input channel facilities are completed by the 100mm Alps fader and Pan control — there is no room for a write-strip, so you'll probably have to resort to a strip of masking tape along the aluminium extrusion.

As is usual on desks of very compact dimensions, the routing matrix has had to be accommodated within the upper end of the fader-travel area. Selection switches are provided for the mix bus and pairs of the eight sub-groups, selected individually via the usual odd/even Pan control logic.

The groups do not necessarily have to be employed for recording, for there is a Direct/Group switch which lifts the channel from the matrix and sends a post-EQ, postfade output from the corresponding tape send. Groups are also paralleled in multiples of eight, allowing you to address as many tape tracks as there are inputs, recording either direct or via sub-group without the need for repatching — a simple to use, yet totally flexible arrangement.


Monitor Level and Pan are handled by a dual-concentric knob, with the source being either the Line input or the tape-return according to the status of the Reverse switch. Monitor EQ consists of two fixed-frequency shelving filters, offering +/-14dB at 100Hz and 10kHz — not exactly a full-spec EQ, but more than adequate for general tonal correction or moderate sweetening. The monitor EQ pots, like their main EQ counterparts, are centre-detented.

The fact the monitor EQ does not use part of the main equaliser, and is visibly physically separate and located within the monitor section of the channel, will certainly enhance the appeal of the S2 to some of the people who have indicated to me that they are simply not comfortable with the 'partially-transferrable EQ' concept.

Monitors have the same PFL and MIDI-controllable Mute facilities as the main inputs. Auxiliaries, however, with the exception of the dedicated Monitor Cue bus, have to be assigned over from the main channel, as previously mentioned. The Monitor Cue bus is entirely separate from the Channel Cue bus, and has its own output; however, the two can be combined via the rather clever stereo cue mix switching. Governed by a Cue mix master level control, it is possible to select any, or all, of Channel Cue, Monitor Cue, Stereo Bus and Monitor Source (which could be a 2-track machine return, for example).


The eight group outputs use the same fader type as the input channels, with group PFL facilities and Group-to-output switching for audio sub-grouping during mixing. Odd-numbered groups always feed the left bus, and even numbers the right, which is not as flexible as individually controllable sub-groups, but probably a necessary limitation given the number of controls that such compact dimensions can reasonably be asked to accommodate.

Groups are provided with insert points — a very welcome feature, and one often omitted. Group metering is via 10-segment LED ladder, calibrated from -20 to +6dB, and changing from green to red at the 0VU point. A ganged stereo master fader is used for the mix bus, doubtless economising both on space and manufacturing cost. On the whole, I still much prefer the greater flexibility of separate left and right master faders wherever possible. Main output metering matches the group's LED columns — a little short of resolution, but adequate nonetheless.


The S2 incorporates four well-equipped stereo F/X returns. Of course, they don't have to be used for effects; they can be used simply as stereo channels, for each return has a Gain control, in addition to Level and Pan, and 2-band (100Hz and 10kHz) EQ. A send to the Channel Cue bus is also included, plus a full track-routing matrix for sending F/X to tape or to an audio sub-group. The PFL and Mute facilities present on all channels and monitors are also incorporated in the dedicated returns, to complete a comprehensive and powerful facility.

There is really nothing missing in the way of basic master facilities; talkback to groups, cues, or both, is available via integral mic, and a 2-frequency (1 kHz/10kHz) oscillator is provided for test and alignment purposes. There is a Headphone output, with its socket optimally located at the bottom right-hand corner, and Control Room monitor switching includes both Mono and Mute facilities, plus alternate monitor system selection. The CR level control is, quite correctly, slightly larger than any other on the desk and therefore easily identified. Such a small point would be hardly worthy of comment, but for the number of designs that get it wrong.

It is typical of the feature-laden S2 that not only are there two sets of 2-track machine returns, but there is also a facility for dubbing, in either direction, between them. In systems that do not include a patchbay, it is not only more efficient, but considerably reduces the strain on cables and connections, to be able to perform such routine copying tasks without pulling-out and re-plugging connectors that were never designed for constant use.

Switching is provided so that each 2-track machine can see either the stereo bus or the other machine at its input. Either 2-track can also be monitored via the CR system, or indeed fed to the cue mix, via the Monitor Source route.


The S2 uses the impressive and much-enhanced Version 4 MIDI Mute Processor, first seen in the Spectrum console, and included also in current versions of the Saber. The system now incorporates the ability to record mute data internally against a time-reference of MIDI clocks and Song Position Pointers. When entered into Record mode, the system waits to see incoming MIDI clocks from either a sequencer or timecode-to-MIDI convertor.

Once running, any change of Mute status will be registered at its correct location, and be correctly reproduced when the clock sequence is run again. 'Playback' of previously recorded mutes is automatic, whilst the system remains in overdub/record mode so you can build up the overall mute picture gradually, concentrating on one section at a time. Recording the mute data internally allows the system to employ its own method of 'chasing' data (adopting the correct configuration of mutes regardless of where the clock sequence is started), rather than having to rely on the capabilities of an external sequencer in this department. The S2 system appears to live up to its specification which claims that the correct mute configuration will be recalled within half a second of start-up.

The V4 MIDI Mute Processor is a model of economy when it comes to controls; just eight switches and a 2-digit LED display cover all the functions of the system. A pair of Increment/Decrement switches are used for data entry, which in general means selecting the Patch number. A Toggle mode is available for the user to check the currently active preset at any time, irrespective of the number presently displayed, whilst Update re-writes the active location to reflect the current status of the mutes.

Further operations, including the user-definable default modes, are accessed as shifted functions, keeping the control area compact without greatly adding to the complexity of operation. The system can be set to operate on any channel (it defaults to channel 16), and although MIDI note on messages are normally used to identify channel numbers and mute status (note number = mixer channel, velocity value determines Mute On/Off), there is also the option to employ continuous controller messages for those whose systems cannot afford to dedicate a channel to the automation. (By avoiding note data and using only controllers not normally recognised by MIDI voice modules, the MMP can share a channel).

Editing is quite simple — any entry in the series of events pertaining to a particular mute switch can easily be erased, using the system's Erase Last, or Erase Forward facility. Both methods are semi-real time however, performed whilst running the 'song'. The former erases the last mute event to have occurred, whilst the latter is more like erasing tape, removing all events occurring in the section actually run. Where greater precision than can be achieved by real-time operation is required, you can dump the data out to a MIDI sequencer to employ its graphic editing facilities to enter, erase, or move mute events, and then load it back again into the MMP.

Once a correct set of mutes has been recorded, it is necessary to transfer the data from the scratch-pad memory, referred to as the Working Song, into one of the 32 nonvolatile on-board Song Memories. This clears the Working Song for new data. Songs can be saved and re-loaded, when necessary, as MIDI Sys Ex dumps.

You can isolate individual channels from automatic mute operation at any time, either because you prefer manual operation (for safety, perhaps) or to use the channel for a last minute overdub without altering mute data already set for the mix.

As an alternative to the real-time recording procedure, you can store and recall up to 33 static 'snapshots' (Patches) of the mute status of the whole desk. (Patch zero is reserved for initialising the desk on power-up, and for providing a consistent configuration for starting 'songs' under synchronisation).

Patches can be recalled either manually, or via MIDI Program number messages. The current Patch number increments automatically when you store (Update), or Recall a patch, so you do not have to advance the system manually when using a sequence of snapshots. Patches can also be used in combination with individual real-time mutes as part of the automated Song data. The configuration of any Patches used within a Song are automatically incorporated within its data, so you don't have to think about saving them separately.

Allen & Heath's MIDI Mute Processor has always been an immensely useful production tool, for non-destructive editing, cleaning-up stray sounds on tape, and general noise-reduction duties, as well as 'track-splitting' (the technique of feeding a single track into two channels with different settings, then switching between them to achieve an automated level, EQ or F/X change). In its V4 guise, it is more powerful and versatile than ever, and yet, if anything, even easier and more intuitive to use, with no external hardware now required other than a source of MIDI clocks.


With this combination of features and performance, it would appear almost inevitable that the S2 will continue the success story of the revitalised Allen & Heath range. It represents remarkable value for money, combining the power of the most advanced MIDI muting system on the market with the large number of useful inputs offered by EQ-fitted monitors, plus the compact dimensions of the in-line configuration. Basic audio performance, specifically mic amp capability and mixing noise, is subjectively on a par with the competition in this sector of the market. A significantly higher calibre of mic amp performance could almost be considered an irrelevance, for the S2 design is nothing if not well matched to the probable working practices of its intended operators. If I read the market correctly, the typical user is envisaged as a small multitrack owner, recording tape tracks via close-miking, and running a number of MIDI instruments in sync on mixdown — the S2 gives that user everything they need, whilst including nothing that is not of actual practical value to this type of set-up.

If you want expandability and MIDI muting in an in-line desk at this sort of price, it is difficult to know where else to look, for there would appear to be no competitor that can presently match the S2 on every one of these features.


Allen & Heath S216-8-2 £1,699 + VAT.
8-channel expander modules £600 + VAT
Allen & Heath S2 24-8-2 £2,299 + VAT.
Allen & Heath S2 32-8-2 £2,899 + VAT.

Thatched Cottage Audio, (Contact Details).


Frequency Response: 20Hz - 20kHz (+0/-1dB)
Distortion: <0.02% THD 100Hz - 10kHz (typically <0.01 %)
Noise: Mic. equivalent i/p noise: -128.5dBu (ref. 150 Ohms source)
Group O/P Noise: -80dB (ref. 0VU)
L-R Mix Noise: -76dB (ref. 0VU)
Crosstalk: Input to unwanted o/p: -80dB (1kHz), -60dB (10kHz)
Mute Attenuation: -90dB (1kHz), -70dB (10kHz)
L-R Separation: -68dB (1kHz), -60dB (10kHz)
Gain (mic in to grp out): 85dB max.
Gain Range: 56dB, continuously variable
Line I/P: -12dB to 42dB
Tape I/P: -10dB
Internal Headroom: +22dB (ref. 0dB internal operating level)
Max. O/P Level: +21dBV (into 2kOhm load)
Multitrack Interface Level: -10dBV (can be +4dBm)
Insert Point Level: 0dBu
Dimensions: 16-8-2: 740mm x 725mm x 130mm
24-8-2: 1000mm x 725mm x 130mm

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Steve Reich

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Hands On: Sony DTC1000ES

Publisher: Sound On Sound - SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.

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Sound On Sound - Sep 1991

Gear in this article:

Mixer > Allen & Heath > S2

Review by Dave Lockwood

Previous article in this issue:

> Steve Reich

Next article in this issue:

> Hands On: Sony DTC1000ES

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