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Author Topic: AKAI MPX820 (1987?) 8 channel mixer  (Read 1840 times)

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Offline chrisNova777

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AKAI MPX820 (1987?) 8 channel mixer
« on: July 09, 2017, 03:22:51 AM »




http://www.muzines.co.uk/articles/the-snap-shot-mix/1530


Quote
As MIDI approaches its fourth birthday, it's being made to do more tricks, to jump through more hoops, and to handle more responsibility than its original designers could possibly have imagined. Far from just being a way for musical instruments to communicate with each other, MIDI has become a means for accomplishing feats of musical and audio control and automation hitherto possible only with very costly, totally proprietary (ie. non-communicating) systems. The last steps on the path to allow MIDI to completely take over automation of the music production process are now being taken. One company on that path is Akai whose new MPX-820 provides MIDI control over a complete 8 into 2 mixing console, at a price of £1399 inc VAT.

EFFECTIVE AUTOMATION


The MPX-820 was originally developed by Zeta Systems, a California-based company currently involved in making MIDI violins, among other esoteric devices, who licensed the technology a couple of years ago to Akai. The latter announced the product in early 1986, but the first review units were not available until mid-November.

About the author: Paul D. Lehrman is a musician, software consultant, and writer, who lives in the Boston area. His article on the production of 'The Celtic Macintosh' appeared in the September and October 1986 issues of Sound On Sound.
Actually, the mixer represents a new level of low-priced studio automation in which MIDI is just one - albeit probably the most significant - aspect of its operation. Like many more expensive automated mixing consoles, the device works by taking digital 'snapshots' of the positions of all of the controls at a moment in time, and recording the data into one of 99 onboard storage registers. These registers can be edited and recalled in any order by an on-board numeric keypad; or by MIDI program change commands; or incremented (up or down) by footswitches or (up only) by pulses recorded on a special tape sync track. The contents of the registers can also be stored on a standard data cassette, and will soon be addressable through a computer, using software currently being developed by a number of third parties (see panel).

It is the completeness of the data storage, and the conformity with the MIDI specification, that make the MPX-80 unique. There are other mixers that use MIDI to control channel on/offs and effects routings, and still others that use their own proprietary codes, sometimes based on MIDI but not totally compatible with it, to control individual channel levels. The Akai MPX-820, however, is the first mixer to include channel and master levels, pans, effect send and receive levels, and even EQ in its internal registers, and to make them accessible by standard MIDI commands.

The implications of such a system are far-reaching. In live performance, the mixer can be called upon to reconfigure itself instantaneously from any MIDI keyboard. In a conventional small studio, its tape-sync function can be used for time-based automation. Where it would seem to be of best use, however, is in conjunction with a sequencer in a MIDI-based studio, where it can provide a degree of precision and flexibility in automated production not previously possible.

Normally, automated mixing consoles work off some kind of clock; they execute pre-programmed changes at precise times. The 'moves' themselves are stored either in RAM or on a medium such as floppy disk, and they are then triggered by a timing pulse, usually derived from a recorded tape track, like an FSK or SMPTE stripe. Editing or changing the timing of the moves can be a cumbersome job, often requiring the user to modify all of the events in a song, or even restripe the sync track, just to change one. When the MPX-820 is used with a MIDI sequencer, however, moving or deleting an event is as simple as changing the position of a program change, and need have no effect on any other events. If the tempo of a tune needs to be altered, there's no need to re-time each mixer change. A sequencer with cut-and-paste or loop functions will manipulate the mixer's instructions the same way it does musical information, making the process of re-programming the mixer essentially invisible to the user.

PHYSICAL LAYOUT


Except for the numeric keypad and large two-digit LED display in the upper right corner, the MPX-820 looks like any other small 8-2 mixer. It fits into a standard 19-inch rack, and is 7U (12¼") high. The eight channel inputs on the rear panel have both low impedance balanced and high impedance unbalanced inputs, and pad switches are provided for each. Direct input and output jacks are similarly provided, and there is a trim pot for each channel on the front panel, along with green (-10) and red (+10) lights.

Each channel has a monitor send (pre-fader), an effects send (post-fader), a panpot, and three EQ controls marked 'High', 'Mid', and 'Low'. The latter controls are labelled '+10'and '-10' at their extreme positions. Neither they nor the pan controls have centre detents. Channel levels are controlled by 100mm slide faders, calibrated from 0 to 10, with extra markings between 7 and 8, suggesting that the manufacturer considers this the optimum operating range.

The master audio section has a single fader for both channels, left and right effects receive controls, and two aux input knobs, each with its own pan control (again with no detents). Two vertical 12-segment LED bar displays show left and right master levels, ranging from —20 to +8. In addition, there is an uncalibrated knob marked 'Fade Time', plus a headphone jack with its own level control.

On the rear panel are jacks for the main stereo outputs, effects send (mono) and receive (stereo), monitor send, and aux inputs (with pad switches) - all unbalanced; jacks for the footswitches to increment program changes up and down; tape-sync input and output jacks; and MIDI In, Out, and Thru DIN connectors. The aux inputs are ostensibly for ganging multiple MPX-820s together, but one could imagine many other uses for them, such as multiple effects returns, or even as two extra instrument inputs. The literature available says that up to eight units can be ganged together, but there seems to be no reason why that number cannot be higher (and the manual makes no mention of such a limit).

The programming section, labelled 'DATA/MODE' has the aforementioned LED display, 10 numbered buttons and two labelled 'A' and 'B', a memory-protect switch, program-incrementing buttons (down and up), and a 'Manual' switch which disables the memory and restores manual control to the mixer.

ELECTRICAL CHARACTERISTICS


Although this looks and feels like an ordinary mixer, a little thought (and a quick look inside) shows quite clearly it is not. With the exception of the input trims and the headphone output knob, none of the front panel controls are actually in the audio path. Instead, they produce DC voltages, which are sent to a digital processor at the rear of the unit, which then controls the audio circuits. It's an elegant system, but it means that the resolution of each of the controls - unlike an analogue mixer - is finite.

Fortunately, this resolution is relatively small. All of the knobs - EQ, sends, receives, and pan - have a resolution in the order of 0.1 dB, although for the EQ and pan controls, this gets broader as you turn them further from the centre. The faders have a fairly consistent 0.5dB resolution at the top and middle of their travel, widening to about 1dB at the bottom. The fader travel is smooth, and is laid out well: the change in level between calibration marking is about 6dB near the top of its travel, broadening to 9dB towards the bottom. At the extreme ends, however, there is no level change - either between 9 and 10 at the top or 0 and 1 at the bottom - meaning a full 20% of the travel is wasted.

Except for the fader extremes, the mixer behaves so smoothly that it's easy to forget that the controls are not acting directly on the audio. Occasionally, however, there seems to be a slight sluggishness in the action of one control or another, probably caused by processing delay. It's only a minor annoyance, though.

The EQ and pan controls have their eccentricities as well. The EQ's are Baxandall-type 'hi-fi' tone controls, with a bandwidth that increases as you move a knob further away from its centre position. The panel markings indicate their range as +/-10, but the manual says they are +/-15dB. In the case of the 'High' control, the manual is correct, except that the corner frequency is 8kHz, not 10kHz as the manual would have it. The 'Low' control, on the other hand, gives +18/-16dB at 50Hz (the manual says 100Hz). The bandwidth of both of these controls is so broad at full settings, that both of them have a 5dB cut or boost effect at 1 kHz. The effect of the treble control is visible, in fact, down to 150Hz, while the bass control operates all the way up to 2kHz. The action of the 'Mid' knob is centred at 1400Hz (the manual says 1500Hz - close enough), +12/-15dB, with +/-5dB points at 400Hz and 4kHz.

An EQ circuit with this much effect on such a wide portion of the audio spectrum can play havoc with levels, and because of the way the level indicators are designed, if you were to turn the midrange control all the way off, it would be absurdly easy to overload the input without the '+10' light ever firing.

Worse, however, is the lack of centre detents on the knobs. The nature of the circuit is such that the unit is relatively forgiving of small changes at the centre of the controls' ranges, but it makes the job of taking the EQ out of the circuit very difficult (especially since there is no dedicated EQ bypass switch). This is an important deficiency in what is supposed to be, after all, an electronic music mixer, in that most synthesists prefer to work without EQ, making the appropriate tonal changes on the synthesizers themselves.

The pan controls, because they are less forgiving near their centre positions, suffer even more from the lack of detents. They are also slightly off - in the unit we got, the 'centre' position gave an output that was consistently 1-2dB too high on the left side.

In most respects, the mixer behaves the way it's supposed to. Effective input noise measures out at -118dB at the mic inputs and -90dB at the line outputs (unweighted), while frequency response (once you manage to get the EQ out of circuit) is quite flat from 20Hz, with a 2dB roll-off at 20kHz. Crosstalk is better than 70dB, both between the left and right outputs, and across the inputs.

The maximum output level is +20dBm, but some of the other choices for levels and gain structures are a little strange. For example, the effects inputs are 20dB less sensitive than the line inputs, which means that your effects unit will have to have a lot of output to be heard. The individual channel outputs, too, are severely attenuated before they reach the main mix bus, and it is impossible to drive a single channel so hard that it clips the main output. This means that under most conditions the optimum operating range of the channel faders is fairly small, and on the high side.

SETTING UP PROGRAMS


Programming the MPX-820 is a very straightforward procedure. Turn off the memory-protect switch, press the 'Manual' button (or the zero key twice - register '00' is the manual register), set all the controls where you want them, and press 'A' followed by the two numbers of the register in which you want to store the current set-up. The state of every control on the desk, except the input trims and the headphone level, is recorded. Whenever you want to recall that setup, you press the appropriate pair of numbers on the keypad, or you use the program-increment functions (either from the front panel, footswitches, or a recorded sync track), or you send the device a MIDI program change.

If you want to modify a recalled program, you move whichever controls need changing and store the program again (in the same or a different register); only the settings of knobs that you have moved will be changed in memory.

Figure 1. Opcode Systems' Akai MPX-820 Editor/Librarian software for the Apple Macintosh (preliminary screen display).


Two American software companies, Opcode Systems and Hybrid Arts, have announced editing programs for the MPX-820 that will allow control settings to be modified in the computer and stored on disk, then loaded wholesale into the mixer's internal memory, just as one can do now with many synthesizers. Opcode's program will work on the Apple Macintosh, while Hybrid Art's product will be for the Atari ST family of computers.

Precise details of the programs were not available at press time, but a preliminary version of the Opcode software shows it to be essentially similar to the company's programs for Yamaha and Casio synthesizers. Programs are stored in banks of 99, and any program can be singled out for editing, at which time a simulation of the mixer's control surface appears on the screen. See Figure 1.

Also stored with each program is the position of the 'Fade Time' knob. This innovative feature allows the user to determine how long a called program will take to execute. It is a 'smart' feature, in that it will produce smooth fades to the desired mixer state from any previous state. The manual says that the knob (which is marked only 'Min' and 'Max') can be set from 40 milliseconds to 30 seconds, but the actual range of times we measured is about 15 milliseconds to 20 seconds. The fades produced by this feature are very smooth, regardless of length or complexity.

The mixer can be set to respond to data on any MIDI channel, and is always in Omni Off mode. It reads 'true' MIDI program numbers - ie. what most synthesizers and sequencers send out as program '1' is received as '0'. This is a little confusing, as you have to remember to subtract 1 everytime you want to call a program externally, and if you send patch number 1, it doesn't call a program - it puts the mixer in manual mode!

Editing is straightforward as well, although there are some serious peculiarities. The question of how to 'show' recalled programs on automated mixers has plagued their makers since day one. Some of the solutions have been moving faders, up and down 'nulling' lights, or external video or LCD displays, and there are probably many others most of us haven't heard about. Akai's solution is to do as little as possible. To find out the 'virtual'setting of a control in a particular program, you have to physically move it. When you go beyond the right point, the LED display blinks, and an extra dot appears, showing you have edited the program. If you move the control back, the display blinks again, but the dot stays on, even if you reset the control perfectly.

Finding the correct 'null' point of any control in this manner can be an exercise in frustration. Because the display only tells you when you've moved past the setting, not when you are on it, then like Zeno's paradox, you can get close, but it seems you can never get it exactly right.

To make things worse, Akai's designers (like those of certain top-class digital processing systems) have decided that a physical control will not start to work at all until you move it past the null point - which means that a major change in the position of a control may have no effect whatsoever, if you happen to be moving in the wrong direction. You have to go back past the virtual position, and then reverse the motion again. This could be disastrous in a live situation where a fader level has to be brought down quickly - because first, it has to be brought up!!

USING THE MIXER


In use in a MIDI studio, these drawbacks are not quite as serious as they might appear. Generally speaking, editing a pre-programmed mix is often just a matter of moving one or two controls slightly, and at that level of complexity, the system is reasonably usable.

In general, however, using the MPX-820 leaves this reviewer feeling a little uneasy. The idea of a mix as being a series of 'snapshots' seems awfully restrictive, and detracts from the feeling that, like a piece of music, a mix should be a living, breathing, thing.

The programmable fade time helps quite a bit, but it makes the assumption that when you do a crossfade (from one program mix to another), you want all the controls to move at the same relative rate. The maximum of 99 'snapshots' for any one piece of music also seems limiting, and precludes a great degree of subtlety in a mix - first of all [**print error missing copy in text**] secondly, because storing each snapshot pretty much requires that you stop the music.

For 'quickie' production chores, however, the MPX-820 is not a bad little box. It's fast and easy to setup, and very easy to learn, and we found that a typical short instrumental track, lasting about three minutes and involving seven synths and a drum machine, could sound pretty good with only 15 or 20 moves. It does require you to think a little differently from the way you might be used to when mixing, and you may occasionally find that doing a certain kind of move is essentially impossible, so you'll have to figure out a way to fake it.

OTHER TOPICS


The manual we received was written in pidgin Swahili. There are plenty of illustrations, however, and as the operation of the mixer is really simple, it's not too much of a problem.

We didn't test the tape-sync function. It looks very cumbersome, as it requires recording a sync track from the mixer, at the same time pressing the 'Program Up' button at each exact moment when you want the mix to change. As this allows for no mistakes or experimentation (if you blow it by only a fraction of a second, you have to start all over), it seems it would help to speed up a session not a whit! We also didn't test the cassette dump function, as we dislike such features on general principles, and we're perfectly willing to wait for the software that will allow a computer to perform the task.

According to the preliminary spec sheet supplied, the unit's internal memory is backed up with a battery, with a claimed life of ten years. The manual says nothing about it at all, however, and if there is such a battery in there (which would make sense), it is certainly not accessible to the user!

Unless you are a student of MIDI implementation charts, you would have no way of knowing that the MPX-820 responds to MIDI controller number 7 (or MIDI volume) - nowhere else in the manual, besides the chart, is this fact mentioned. When a MIDI volume command is sent to the Akai mixer, the master volume changes accordingly, in real time. The only apparent advantage to this function is that initial and final fades can be handled by controllers (a synthesizer's pitch-bend or modulation wheel, for example) instead of program changes, leaving two extra internal registers free for something else.

OVERALL EVALUATION


Although the MPX-820 has many fine ideas built into it, there are too many small things wrong with it.

That the EQ controls have no detents is annoying, but that the pan controls have none is criminal. The bandwidth of the EQ controls is far too wide to be effective. The single effects send is limiting, especially considering true stereo reverbs are now becoming more available to the budget user. The monitor send could conceivably be used as a second effects send, but since it is pre-fader (and the effects send is post-fader), it would not be easy.

The gain structure is quite restrictive, and could benefit from higher levels throughout. The fact that the input trim controls are not automated means that reproducing a mix precisely (especially an old one) can be much more of a chore than necessary. The 'Fade Time' control desperately needs some calibration. The present editing system is clumsy and slow. Having software will help enormously, and we can hope that someone will eventually come up with an editor/librarian for all the many computers in general use by musicians.

On the plus side, the MPX-820 gets high marks for being very easy to understand and to use, once the concepts involved are understood. The automation functions, as far as they go, work remarkably well. The sound quality is good, and the low noise figures are particularly impressive.

The Akai MPX-820 is an important first step towards MIDI-based studio automation. But (and I welcome debate on this) I believe that the 'snapshot' approach is the wrong way to go, especially considering that MIDI has literally hundreds of potential discrete controllers available, which if used properly, could do a credible job of running a very complex mixer in real time. (There are some manufacturers, incidentally, who are right now planning to subvert the MIDI spec by building mixers that will use note-ons and velocities to control their functions, on the grounds that most currently available sequencers can edit notes much more easily than they can edit controllers. To these people I can only say 'Shame on you!' If the entire industry shared that attitude, 'FM' would still have something to do with radio!)

If I were in the market for a MIDI-automated mixer (and I am), and I could afford to be a little patient (which I can), I would wait until a mixer comes along that uses MIDI controllers, or some kind of combination of 'snapshots' and real-time control, so that I could be assured my mixes would feel as 'human' as possible. Somehow, I doubt the wait will be too long.

Special thanks to Walter Lenk for technical assistance with this review.

MRP £1399 inc VAT.