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LA Audio Millennium MPX1

Mic Processor By Paul White
Published August 1997

Voice channels are gaining in popularity with the rise of digital, providing an easy way of recording high‑quality signals without having to go through a mixer. Paul White rates the latest in the breed.

Last year, every company had to have a small mixer in their portfolio; this year it seems that no respectable manufacturer can get by without having a voice channel as part of their product line. The channel concept isn't new, but this market was rather specialised until digital recording came along — then studio owners suddenly realised that they could make better recordings if they bypassed the mixer altogether. Now, with tapeless recording becoming the norm rather than a specialist sideline, mic channels have moved into the mainstream, as they provide a compact and affordable means of getting quality signals into these systems. LA Audio are one of the latest companies to jump on the bandwagon. Waiting until now to launch their contender has given them a chance to see what their competitors are up to, so it isn't necessary a bad thing. Even so, I'm sure that if you listen carefully, you'll be able to hear the creaking and groaning of a wagon axle that's already loaded well beyond its design capacity!

LA Audio have got off to a bit of a sticky start by giving their voice channel exactly the same name as Lexicon's latest multi‑effects processor, but few people will mistake one for the other. LA's MPX1, aside from being entirely devoid of blue paint, is completely analogue, and combines a mic/line preamp, an expander gate, a compressor and a 4‑band equaliser in a 1U, mains‑powered rack case. Though the sections are arranged in series, the preamp, compressor, equaliser and main output stage have their own inputs and outputs on the rear panel, enabling them to be used individually or chained in a different order. The compressor also has a side‑chain insert point, so you could patch in the equaliser for de‑essing, though a basic de‑essing filter is thoughtfully supplied as part of the compressor. All the individual ins and outs are on unbalanced jacks, with the exception of the mic/line input and the in/out connectors relating to the output section itself — the main output is simultaneously available on both a balanced XLR and an unbalanced ‑10dBV jack.

Input Stage

The best way to cover a device like this is to take it a section at a time, starting with the preamp. Obviously, the mic preamp is very important, because if it isn't better than what you'd get in a typical console, there's no real advantage in buying a unit such as this. LA have based their preamp stage around the SSM 2017 chip, which can, in a carefully designed circuit, out‑perform many mid‑priced console mic amps. A single rotary pot sets the gain of both the mic and line inputs, and a Line button is used for mic/line selection. Phantom power is switchable, and there's a phase reverse button and a switchable high‑pass filter operating at 75Hz with a slope of 12dB/octave, but input metering is restricted to a single peak LED.

A balanced TRS jack handles the line input, though this can also be used unbalanced. A rear‑panel push‑button and a second unbalanced input jack provide an alternative DI input with a 500kΩ input impedance, suitable for use with electric guitars or basses. The output jack is normalised to the input of the expander and compressor section.

Expander And Compressor

In order to provide a simple means of cleaning up signals prior to compression, the MPX1 includes a fixed‑ratio, variable‑threshold expander with fixed attack and release times. The ratio of the expander is 2:1, a good compromise between smoothness of operation and effectiveness of noise reduction, and a single green LED shows when gain reduction is taking place.

Channel‑type products often compromise on EQ, but LA Audio have stuck out for the full four bands

The compressor is based not around the FET circuit used in some of LA's vintage‑sounding designs, but around the THAT4301 VCA chip, a popular chip used in numerous compressors and console VCA automation systems. Rather than taking the soft‑knee approach, the compressor is a conventional hard‑ratio type with fully variable threshold and ratio controls. No attack and release pots are fitted, as the control is largely programme‑dependent, but there are independent switch options for both fast and slow attack and release characteristics. A conventional make‑up gain pot is fitted, and a readout of the gain reduction is provided by means of a six‑section LED meter in the master section. Two further buttons provide bypass and a de‑essing filter, the latter of which is switched into the side‑chain to make the compressor more sensitive to sibilant sounds. The way in which the filter is configured makes the compressor 8dB more sensitive to frequencies around 8kHz, which is where many sibilance problems occur. Though this isn't variable, it's a welcome addition and, if more precise filtering is required, it's always possible to patch the EQ section in via the side‑chain send/receive jack. In addition to separate in, out and side‑chain insert jacks, the compressor also has a Link jack, allowing two units to track stereo signals.


Channel‑type products often compromise on EQ, in order to get as many features as possible on the front panel, but LA Audio have stuck out for the full four bands. The high and low sections are fairly conventional shelving filters, providing up to 15dB of cut or boost at 12kHz and 80Hz respectively, while the two mid sections are fully parametric. The lower mid can be swept from 20Hz to 1kHz, while the upper mid goes from 500Hz to 20kHz, so there's no problem in reaching those awkward bass frequencies. The Q controls are basically splined pot shafts rather than proper knobs, presumably to save space, and they offer fully variable bandwidth, from three octaves to just one semitone. There's a small notch in the end of the 'knob' to act as a pointer, but if the MPX1 has an ergonomic weakness, this is probably it, as it's quite difficult to see. The EQ has its own Bypass button, though there's no status LED, and a further button brings in a 6dB shelving low‑pass filter at 12kHz, to take out unwanted HF. This is switched separately to the EQ, and so may be used on its own if needed. This type of filter is useful in combination with HF‑rolloff on the main EQ, to remove excess noise and fizz from DI'd guitar parts, though I'd have preferred to see a steeper curve used, ideally 12dB/octave or even more.

That leaves only the output stage, which provides a balanced drive to the output XLR, and an unbalanced, ‑10dBV output for connection to semi‑pro equipment or computer soundcards. This section also houses the compressor gain reduction meter and an output level meter.


Clearly the MPX1 is aimed at the cost‑conscious end of the market, but the designers have really done their best to build in quality where it counts. For example, the preamp is better than you find on many mid‑priced consoles, and it's useful to have the DI option as well as the more obvious mic and line inputs. Engaging the compressor also brings in the expander, so if you don't want to use that, you have to turn the threshold right down, but the compressor itself provides a happy medium between invisible compression and compression as an effect. Used in moderation, it smooths out variations in level, with very little sign that processing is taking place. However, at high ratios, with a lot of gain reduction, the effect becomes more obvious, especially when a fast release time is used. If anything, the compression is more subtle than on some of LA Audio's more deliberately vintage‑sounding FET designs, but in the context of this processor and the way it's likely to be used, that was probably a sensible decision. The expander is simple to use, but it can tend to chatter a bit in noisy environments, so you have to set it up carefully. Also, it's important to use a good mic stand for serious recording, preferably with a shockmount, as stand‑borne vibrations can also trigger the expander if the threshold is set fairly low.

The equaliser is actually very competent, and you don't usually need much of it to knock a sound into shape. It's positive and clean, and, unless you over‑use it, you don't end up with harsh highs or boomy lows. I also approve of the very wide sweep range, especially at the low end, where you can get right in amongst all those nasty, boxy frequencies and trim them out.


Within its price range, the MPX1 performs well in all areas, making it a cost‑effective solution to getting mic, line or instrument signals to tape or disk, with or without processing along the way. I like the flexibility of being able to separate all the different processing 'units', which is also good news if you want to use some of these sections while mixing, and though some corners have been cut, these are generally in areas you can live with. The Q pots and their invisible markers, for example, could be more friendly, and on a more expensive unit more buttons would have had status LEDs. Judged purely on sound, though, I'd say that the only section I wasn't completely thrilled with was the expander, and even that's not bad for a simple, one‑knob clean‑up tool. On top of the obvious features, the compressor's de‑essing option and the EQ section's 12kHz low‑pass filter are genuinely useful bonuses, and the overall styling is tidy, with good engineering evident throughout. The voice‑channel bandwagon is a crowded one, and different units generally offer different benefits, but as a good all‑rounder that includes a flexible EQ section, the MPX1 has a lot going for it.

Inside Story

Removing the MPX1's cover reveals a simple, one‑board layout with all the controls and sockets connected directly to the double‑sided, through‑hole‑plated PCB, to eliminate wiring. In fact, the only visible wire is a ground cable connecting the mains earth to the chassis. The general standard of construction is excellent, though the plastic‑bodied XLRs don't appear to have their pin 1 (ground) connections bonded directly to the chassis at the nearest point, in accordance with AES grounding recommendations. The only obvious weakness I can see in the design is that the use of normalised jacks to link the sections is prone to eventual problems from dirty or oxidised contacts, but at least they're easily accessible, should cleaning be required. It might be prudent to treat these with a contact enhancer or deoxidising solution when the unit is new.


  • Creditable range of features for the price.
  • The various sections sound good, and there's a full four bands of EQ.
  • Separate input/output access to all sections.


  • Q pots are small and fiddly.
  • Expander can be rather abrupt on some material.


A well‑designed, attractively priced unit that delivers sonic quality where it counts, at the expense of a couple of minor ergonomic flaws.