Rane MPE14 MIDI Programmable Equaliser
Dynamic MIDI control of EQ curves is only one of the creative benefits of this stereo 14-band equaliser, which offers tremendous tone-shaping power to those enlightened enough to explore its functions. Dave Lockwood sees the light and reports back.
The Rane MPE14 is a stereo, 14 band, 2/3 octave, programmable equaliser, which features not only memories to recall preset equalisation curves but also real-time control via MIDI. Although digitally controlled, all audio stages remain totally analogue, so you can count on the MPE series - which also includes a 28 band 1/3 octave unit (MPE28) and a four-channel, 7 band unit (MPE47) - sounding every bit as good as Rane EQs always have.
The MPE14 is housed in a 1U rack case, with an external PSU, although not one of the much reviled lightweight 'DC mains adaptor' type. This is a very substantial unit with an in-line female IEC input and a cute locking miniature multipin output (18V AC). There is no power switch, but this is unlikely to be a problem for most users when racked. The rear panel simply offers electronically balanced XLR In and Out for the two channels, with ¼" 3-pole jacks in parallel, plus MIDI In, Out and Thru. Input impedance is quoted at 20kOhms, with maximum input/output level at +20dBU (0dBU = 0.775V rms), giving plenty of headroom. Output impedance is 300 Ohms.
Round the front, everything is controlled by soft rubber switches, similar to those on the original Alesis MIDIverb. These are a bit low on tactile feedback, and more than once I found I had failed to properly register a press when I thought I had, but there is almost always some form of status confirmation to verify successful entry (provided you are looking in the right place!) so you can't go too far wrong in practice. There are two LED numeric displays to keep you informed: a 'System' display in red, showing memory location number, MIDI channel, Controller numbers and so on; plus the 'Equaliser' display, in green, which indicates the actual boost or cut levels of individual filter bands. Although some of the buttons are dual-purpose, accessed via a 'Function' key, there are no hidden menus; everything is clearly legended on the front panel, and the operating system could not be more friendly. This is a sophisticated device, yet one you can use virtually straight out of the box, with hardly any required reading. I would, nevertheless, thoroughly recommend the owner's manual to prospective users, for it is a fine example of clarity combined with sufficient depth, but with a light touch where appropriate and some genuine wit - if only more equipment manuals were like this!
Operating the MPE14 is simplicity itself. The unit powers up displaying the last used memory location. There are 128 locations (referred to as Stored Memory) with an edit buffer (referred to as Working Memory) used for setting up your required curve. The setting in Working Memory is always what you hear, so you can't really go wrong, you just have to remember to store anything that you want to keep, for Working Memory is volatile. Stored Memory presets have to be recalled into Working Memory to use them, or for further editing.
In 'Normal Operating Mode', which is what you are in when you are not editing something, the frequency band selector switches double as numeric keys for direct entry of memory location numbers. Numbers below 10 do have to be entered with a leading zero (eg. 07), and above 99 requires the use of a dedicated 'Hundred' button, but apart from that it is all quite straightforward. The Up/Down buttons (a nice bit of plain English there, who needs Increment/Decrement?) may also be used for changing the selected preset, with rapid scrolling achieved by holding down either button, as you might expect. If Bank Hold is activated, the 'tens' digit (and 'hundred' if selected) is frozen, allowing single key entry program selection within the selected bank, for rapid access. The system can be protected by two levels of 'Lockout': level 1, which allows the user to only select stored curves; and level 2, which disables the front panel completely, to prevent unauthorised interference. The owner is given the opportunity to specify a three-digit security code, to be used to enter and exit Lockout modes, although you are also advised of a universal code to get you out of trouble, if necessary.
Setting up a curve is achieved by pressing the EQ switch to enter the 'EQ Edit Mode', with two LEDs to tell you whether you are working on channel 1 or 2, or both. The switch simply toggles round the three options and then returns you to Normal mode, before going round again, so you are never far away from whatever mode you are seeking. When both channels are selected, they are equally affected by any changes made to each frequency band. The ability to set up identical curves for both channels simultaneously is one of the greatest assets of programmable stereo equalisers, for it really does make life so much easier when setting a curve for EQing a stereo mix. Having initiated the edit procedure, it is simply a matter of pushing the frequency button for the band you wish to edit, and then using the Up/Down buttons for cutting or boosting. The green LED 'Equaliser' display shows the figure for each band as it is selected, with a range of +12 to -15dB, adjustable in 1 dB steps. There is also a Level parameter for each channel, which can be similarly edited, in 2dB steps, providing gain to compensate for the EQ process where necessary.
The MPE14 offers filters centred on the standard 2/3 octave ISO frequencies: 40Hz, 63Hz, 100Hz, 160Hz, 250Hz, 400Hz, 630Hz, 1 kHz, 1.6kHz, 2.5kHz, 4kHz, 6.3kHz, 10kHz, and 16kHz. There is a fixed sub-sonic filter - an 18dB/octave Butterworth configuration active at 15Hz, whilst overall system response is quoted as 3dB down at 15Hz and 45kHz. Unlike some designs, the bottom (in this case 40Hz) band does not appear to have a shelving characteristic, so you just might find yourself with some signal in the 20Hz region that you want to get rid of, but can't quite get at, particularly in a live performance context. On the other hand, you can lift bass fundamentals without dredging up any sub-sonic 'mud', so it is a fair compromise, but one more frequency band would not have gone unappreciated.
"This is a sophisticated device, yet one you can use virtually straight out of the box..."
'Constant Q' filters are used in this design, which means that the bandwidth, or 'Q', of each frequency band remains the same regardless of how much it is boosted or cut. In many equaliser systems the bandwidth alters with gain, achieving the specified sharpness and therefore selectivity only at maximum cut or boost. More judicious use of the gain controls produces a much broader-based filter, which will have a more subtle effect, and which can in fact be easier to set up in some circumstances, but which is less predictable and precise.
Interaction between filter bands is another important facet of EQ specification, and the MPE Series system is described as an 'Interpolating Constant Q' design - which is a nice way of suggesting it displays a bit of intelligence. When adjacent bands are boosted, the net result is a single combined bell-shaped response centred between the bands. When all bands are boosted or cut by the same amount, the result is near enough a flat response again - very impressive.
All changes made whilst editing are heard as you make them, and the process really does soon become almost as instinctive as using a conventional graphic equaliser. The only thing missing, of course, is any form of actual 'graphic' representation of the curve itself, from which the graphic EQ takes its name. Some programmable systems include small LCD displays in order to be able to show the curve in some form. Although I personally don't have difficulty in visualising a frequency response simply from numeric data, I found mixed opinions among my colleagues as to the benefit of actually 'seeing' what you are doing.
Having set up your desired curve, you can move it from Working Memory (the edit buffer) into Stored Memory, at any of the 128 locations, using the dedicated Store button. One press prompts you to enter a location number, and a second press completes the save - dangerously too easy really, for there is no facility for protecting certain curves already in memory and if you happen to forget which locations contain something valuable, you can very easily lose them by overwriting the memory. As with effects units, devices with LCD displays have the advantage of being able to offer the facility of naming your creations, which makes this kind of error much less likely; but as it is, it will probably pay to keep some form of written record.
A blank 'patch sheet' is provided for photocopying, so you can note down all the parameters of a really important setup. But if that seems too much like defeating the whole purpose behind the unit, then you can take advantage of the MIDI Dump facility, which will allow you to save your creations one by one, or in bulk, to any suitably equipped MIDI recorder/sequencer or data filer system. I understand production units will be shipped with some 'powerful factory presets' on board, which could be quite interesting if they come with recommended usages, but I can't comment on these as my unit had 32 'flat' presets!
"The ability to set up identical curves for both channels simultaneously is one of the greatest assets of programmable stereo equalisers..."
When equalising, it is always important to frequently refer back to the original signal, for otherwise it is all too easy to lose track of what you are trying to achieve and over-EQ as a result. With this in mind, the MPE14 offers dedicated individual Bypass switches for each channel, plus the ability to quickly compare the contents of Working Memory with Stored Memory while you are editing. In EQ Edit Mode, holding down the Memory button temporarily reverts to the stored curve, making A/B comparison between the preset and your current edit very simple. As the difference can sometimes be very subtle, and the soft rubber switches are a bit vague, it is probably a good idea that the compare mode is verified by a letter 'C' appearing in the Equaliser display!
Simultaneously pressing both Up and Down buttons during editing activates a 'Clear' or reset function which zeroes, or sets to 'flat', the parameter currently being edited. If no parameter has yet been selected, then the whole channel will be reset - an important feature, for zeroing would otherwise be an extremely tedious job.
Overall, a parameter-based system is bound to be less instinctive and a bit slower to set up than a conventional graphic, but with familiarity, and bearing in mind that you can set both channels at once, it is not actually that much slower in practice. Still, given all the other advantages, I am certainly quite content to compromise.
Two EQ curves can be combined on the MPE14, producing a compound curve that represents the sum of the two. One curve must be in Working Memory, while the other is in Stored Memory. Activating the Curve Weighting function then intelligently combines them and shifts the gain of all bands up or down if necessary, to ensure that the result stays within the normal maximum range of +12 and -15dB. Only where a combined curve would produce simultaneous over-range and under-range figures does the system have to limit the gain in any band to the maximum available, but even then it evens out the total amount of 'error' and centres the result.
MIDI functions on the MPE Series are quite sophisticated, offering not just simple recall of presets via MIDI Program Change messages, but real-time 'curve-bending' with Controller messages, as well as full SysEx dump facilities and remote control between units. A MIDI Mapping feature is also offered, so any Program Change number can be made to recall any memory location, for maximum operational convenience, in any system.
"All changes made whilst editing are heard as you make them, and the process really does soon become almost as instinctive as using a conventional graphic equaliser."
Setting up the MIDI Map is simple, as there is a dedicated Map button. Press 'Map' and you are prompted for a Program number, followed by Memory, which prompts you for the desired memory location number. Repeat until all the necessary map entries are complete, and it then only remains for you to set the required MIDI channel, or select Omni mode, as appropriate. If Omni is on, and Program numbers are being received on all channels, the set MIDI channel number remains as the transmitting channel for this device. Provided Program Change Output is enabled, the MPE14 will transmit a Program number, perhaps to another MPE equaliser, whenever one of its internal memory locations is selected.
This facilitates very easily operated synchronised EQ changes in multi-unit systems, such as those often used in high quality public address installations in conference centres and arenas. A specific 'Speech Curve' and 'Music Curve' is often used - one for maximum intelligibility and the other for maximum quality, for example. A Device ID number can be assigned to every MPE in the system, so that in a particularly large setup only those devices which share the same ID number will recognise one another.
Two types of System Exclusive message can be enabled for transmission to other MPE equalisers: Key Scan messages, which in Key Scan Echo mode constantly monitor and transmit the status of the front panel switches, allowing slaved devices to follow any changes made to the master; Parameter Echo messages which, with Parameter Echo similarly enabled, will transmit information such as altered data values during the edit process. I am sure that simultaneously editing a stack of MPEs in Key Scan Echo mode is great fun, but in practice you would probably be more likely to edit one, and then transmit the result as a SysEx dump, for later recall via a simple Program Change message.
I can verify that Key Scan and Parameter Echo modes can get rather data intensive at times, and are not the sort of thing you want sharing a MIDI bus with note data if you can possibly avoid it. The MPE14 is decidedly not keen on seeing its own MIDI output returned to its input, and locks up the control panel when 'MIDI looped'. It continues to pass audio faultlessly, however, and normal functioning resumes as soon as the loop condition is removed.
Three types of data dump are possible: Working Memory, ie. the current program; Stored Memory, which dumps the whole set of memorised curves; plus the MIDI Map, which can be dumped as a separate item. The full memory set is transmitted as four blocks of 1200 bytes each, which shouldn't be too intense for any MIDI storage device these days, but might give some older generation units a hard time.
"You have got to be doing something pretty extreme before you can provoke the Rane MPE14 into producing any audible anomalies..."
When switching between different EQ programs, a 'Ramp' step size can be entered to limit the rate of alteration, thus avoiding the signal break-up that often occurs with abrupt changes of response. A Ramp value of between 1dB and 27dB can be specified, with 27dB representing the step from +12 to -15dB, the largest possible swing on the MPE unit. Changing in 27dB steps therefore means there is effectively no ramping, ie. instant change, whilst a 1 dB step size would cause a smooth crossfade effect, with the time taken being dependent on the number of steps to be executed; in other words, if the two curves are not much different, it is not going to take very long. You have got to be doing something pretty extreme before you can provoke the Rane MPE14 into producing any audible anomalies, but if you do, the ramping feature can be relied upon to smooth it out for you.
Finally, the MPE14 offers what it calls an 'Expression Mode', which allows real-time manipulation of EQ data via MIDI Controller or Channel Pressure messages. Expression Edit mode is entered via the Express button, and you are prompted to enter a Controller number between 0 and 120, in the System display window. There are three other options beyond 120 — 'AFt', for Channel Pressure (Aftertouch); 'ALL', which reads all Controllers and Aftertouch; 'dET', which activates the MPE's Auto-detect function. In this mode the MPE14 will assign the next valid message received as the controlling source.
Having selected the Expression control source, each EQ band can then be assigned a 'vector', or direction in which it will move in response to the Controller. Pressing a frequency band button toggles it around the three available options: '+1' for a positive vector, or boost; '-1' for a negative vector, or cut; with '0' indicating that the band will remain unaltered. When the Expression Controller sends data to the MPE, the amount of boost or cut applied is then proportionate to the Controller setting. A maximum Controller message value of 127 will produce a maximum response of either +12 or -15dB, according to the vectors assigned.
What this actually sounds like in practice rather depends on the curve you have selected. Totally radical real-time performance effects can be achieved by cutting all the middle frequencies whilst boosting top and bottom, or vice-versa. But perhaps the most successful keyboard orientated usage, for me, was the obvious assignment of a broad-based top end boost to the Aftertouch parameter, to produce a pressure sensitive 'brightness' control for synth voices and samples that do not already have this capability.
Even more interesting was using the MPE14 in a problem-solving context, such as attempting to salvage a piece of off-mic vocal in an otherwise excellent take. Off-mic phrases don't just drop in level, they also lose their high frequencies, and above all the upper-mid 'presence' frequencies. With a MIDI sequencer running from timecode, it proved possible to record a Controller movement which could then be repeatedly time-shifted and re-shaped, in conjunction with different vectors and frequency selection, until the optimum result was achieved. As you might expect, with the ability to go on fine-tuning the parameters practically indefinitely, time permitting, such audio 'repair work' can be carried out infinitely more successfully in the manner described above than with the old method of simply punching an EQ in or out, or riding the EQ gain in real time.
"A MIDI-controllable EQ is not a keyboard player's gimmick, it is potentially one of the most seriously useful studio tools of the MIDI era."
Having programmed the 'fix-ups', I made a safety copy by bouncing onto another track, but on the mix I ran the MPE dynamic EQ 'live' from the sequencer, to preserve the maximum quality, producing the most successful 'salvage' I have ever heard! A MIDI-controllable EQ is not a keyboard player's gimmick, it is potentially one of the most seriously useful studio tools of the MIDI era.
The Rane MPE series of MIDI equalisers will be employed in a wide variety of applications, I am sure. In omitting the spectrum analysis functions now almost inevitably being found on similar units, such as the Peavey Autograph [reviewed SOS March 1990] and the up-market TC Electronic TC1128, I feel Rane may have correctly recognised that such facilities will prove irrelevant in many situations, and indeed that the temptation to slavishly 'use and obey' real-time analysis (RTA) can often lead to less than optimum results.
At the heart of the MPE14 is a very good analogue equaliser which behaves predictably, is very precisely controllable, and above all sounds nice. Of course, like any high Q, multi-band design, it can also sound thoroughly nasty if you want it to, or if you really don't know what you are doing - but that is the trade-off for high selectivity and precision. The digital control stage which facilitates the memory and real-time functions is very well thought out and faultlessly implemented, to provide a highly transparent operating system to the user.
This is a powerful product, excellently specified with impeccable THD and noise figures and robustly built, which perhaps only fails to satisfy in the tactile domain, for I dare say there will be few users who will not eventually come to curse Rane's choice of soft rubber switches. Still, it could have been worse, they could have been membrane switches!
Rane already deservedly enjoy an excellent reputation amongst professionals for their equalisers, and I am confident this will be further enhanced by widespread acceptance of the MPE Series in all the many different fields of audio work.
MPE14 £799.25 inc VAT.
Music Lab, (Contact Details).
Review by Dave Lockwood
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