Focusrite Platinum Mix Master

Paul White tries a new analogue mastering processor that combines expansion, compression, EQ, width control and limiting in a single device.

Home mastering has been popularised by such devices as the all‑digital TC Finalizer, Dbx Quantum and Drawmer 2476, but a great many professional mastering engineers like to use analogue as well as digital tools because of the way they sound. Focusrite's more esoteric analogue equipment is to be found in a number of high‑profile mastering facilities, but now the company have added an integrated mastering processor to their popular Platinum range, placing it within reach of the project studio owner.

The 2U Mix Master is an all‑analogue stereo processor. However, the rear panel has a bay that accepts an optional 24‑bit/96kHz converter for those who want to feed directly into a digital recorder or other digital processor, though this option was not available at the time of review. All the most common mastering tools are provided in this one box, starting with an optical expander for cleaning up low‑level noise between songs or during pauses. This is followed by a three‑band compressor, a three‑band equaliser with parametric mid control and a spatial enhancer for adjusting the stereo width of the finished mix. The output circuitry also includes a limiter which can be switched in to prevent clipping at either the analogue outputs or at the input to the optional converter stage.

In addition to the main stereo inputs and outputs, which are provided on both balanced jack and XLR connectors (operating at nominal levels of ‑10dBv and +4dBu respectively), there's also a pair of direct inputs that allows a second stereo signal to be mixed into the main signal path just prior to the output limiter.

Controls

The rear of the Mix Master not only has the main pairs of balanced and unbalanced I/O, but also useful Direct Input connections for mixing in extra signals immediately before the output limiter.

The expander stage has fully variable threshold and release controls, and its optical gain‑cell circuitry gives it a fairly soft switching characteristic so that its operation isn't too abrupt. There's also an illuminated bypass button and an eight‑stage gain‑reduction meter that lets you know how much gain reduction is being applied. Under normal circumstances, the expander would only operate at the start and end of a song, but it is gentle enough to be used to dip low‑level signals if you set the threshold and release time carefully. The trick is to keep an eye on the gain‑reduction meter in order to see how often the expander comes into action and by how much it reduces the gain.

Compression is applied over three separate frequency bands, and again this uses optical circuitry to give a smooth and musical response. Separate 11‑section LED gain‑reduction meters monitor the amount of compression taking place in each of the bands and all three are controlled by common Threshold, Ratio, Release and Make Up Gain controls. Ratio is selectable in six steps, from a gentle 1.3:1 up to 5:1. Level Trim controls allow the high and low band levels to be adjusted by up to ±10dB, while a Slope control shifts the low/mid crossover point from 200Hz to 100Hz as well as changing the crossover slope — when switched in (the 100Hz position), an inductor circuit comes into play that tends to enhance and flatter the bass end by introducing a hump at around 90Hz.

Multi‑band compression is generally the best option for music mastering as it prevents excessive dynamics in one part of the frequency spectrum (particularly the bass end) from modulating levels in other parts of the spectrum — each band works more or less independently depending on how the spectrum and dynamics of the music are changing. But just occasionally, this can lead to unnatural side effects, so Focusrite have added a Lock button that makes all three bands track together, and in this mode the result is more like what you'd expect from a full‑band compressor.

There's no variable attack time, but instead there is a button to give a choice of fast or slow attack. The rotary switch Release control provides four preset release times or two programme‑dependent modes, one fast and one slow. Programme‑dependent modes are useful when the music character is varying so much that a fixed setting is too inflexible. The conventional Make Up Gain control comes at the end of the chain, adding up to 15dB to the signal level to make up for level lost through compression, and there's a clip LED that warns when too much is being applied. It's important to note that if you intend to use the output limiter, the compressor's output level needs to be as high as possible without its overload LED coming on. A bypass button is fitted to take the compressor out of circuit.

Next in line is the equaliser, which again has been designed with mastering requirements in mind. The LF and HF shelf sections permit up to 10dB of cut or boost and offer three selectable corner frequencies as well as a Tilt position. Tilt works as a very gentle EQ setting with a slope of only around 2dB per octave starting at around 1kHz. The MF section is fully parametric and covers the frequency range 100Hz to 10kHz with the aid of a x10 button, allowing it to be tuned anywhere between the upper reaches of the bass end right up to 10kHz, where it can be used to add air and gloss. Q is variable from 0.4 to 1.5, and as with the HF and LF controls there's a ±10dB gain range. A bypass button is provided along with an overload LED that indicates when excessive EQ boost is causing clipping. If this happens, the compressor make‑up gain control may be used to reduce the signal level feeding the equaliser.

The output stage is dominated by a large meter panel that shows the output level (or the input level if the Input switch is pressed) in 16 steps from ‑40dB to clipping. There's also a phase meter that checks for excessive left/right phase shifts that may cause mono‑compatibility (or vinyl cutting) problems. This shows 0 to 180 degrees in seven stages, with a bright blue LED at the 90 degrees mid‑scale position. Persistent phase difference above 90 degrees should be avoided if mono compatibility is to be preserved. This being the case, a mono monitoring button might not have been a bad idea, but none is provided.

However, you can use the Spatial Enhancer section controls to hear the mix in mono if you wish — when the Image button is pressed in, the Width control may be used to widen or narrow the stereo image. This works on the traditional 'sum and difference' method so its contribution is entirely mono‑compatible. A balance control also allows the user to make a 3dB adjustment between the left and right signals when the Spatial Enhancer is active.

That leaves the Output Trim control (±6dB) and two further buttons for bypassing the Effects (expander, compressor and EQ and Spatial Enhancer) and the limiter. Four red LEDs over the Limiter button show the amount of gain reduction applied by the limiter, up to a maximum of 6dB.

Using the Mix Master

When evaluating the Mix Master, it's important to keep in mind that it is designed specifically for mastering, not for general‑purpose use. For this reason, the available compression ratios are lower than you might find on a general‑purpose compressor, and similarly the EQ range is ±10dB rather than the more usual 15 or 18dB. Unless there's something seriously wrong with the original recording, this provides more than enough range to add the final polish, and because the controls cover a smaller range their operation is more precise. On the other hand, the use of the conical rubber knobs (a hallmark of the Platinum range) does make precise adjustment less easy than it would have been with larger knobs, and some of the switched controls are quite stiff. I reviewed a pre‑production unit, so perhaps these will be less challenging on the production models.

As to the audio performance, this is classic Platinum all the way through, with an audio bandwidth extending from 5Hz to an astonishing 200kHz (+0/‑2dB). The expander is smooth and forgiving, providing you set the threshold sensibly, while the compressor is capable of applying massive gain reduction without causing pumping or other disturbing artifacts. The Trim controls provide the opportunity for a little gentle spectral balancing, and I found the two auto‑release settings very helpful when processing complex mixes. Pushing in the LF Slope Adjust button beefs up the bass end in the kick drum region of the spectrum nicely.

Though the EQ section only has three bands, and of those only the mid‑frequency section is fully parametric, the fact that it's optimised for treating complete mixes means that it really doesn't need to be any more sophisticated. The parametric mid is surprisingly inoffensive when used in boost mode and the different shelving options available to the HF and LF sections mean that the spectral extremes can be adequately controlled without the result sounding strangled or overprocessed. I found that it was possible to apply quite generous amounts of EQ without compromising the sound quality, and there's none of that nasty phasiness that you get with some budget console EQs.

The output section has little influence over the sound, though if you wind up the level so you hit the limiter, it's possible to get a bit more perceived loudness for a given peak level. Providing you don't allow the limiter to trim off more than three or four decibels, it works very transparently, and if you find you don't need it then it can be bypassed. Having control over the stereo width and balance is also useful and most of the time, half of the available width expansion is enough to do the job. I also liked having the phase meter, and though it doesn't tell you everything you might want to know about the stereo image, it provides a useful guide as to whether the left/right phase differences are excessive.

Summary

The Mix Master is very easy to use, and because the controls have been optimised for mastering applications, it's actually quite difficult to make anything sound bad. The compressor evens up levels and helps integrate the sound without removing the dynamic detail and without introducing audible level pumping, while the EQ is very gentle and mild‑mannered. Even the expander is more polite than most, though you still need to take care that you don't truncate the ends of fades.

Overall, the Mix Master is an enjoyable box to work with and provides all the essentials required to turn a decent mix (whether analogue or digital) into a sweet‑sounding master. In some ways it seems less aggressive than its all‑digital counterparts (it polishes a mix rather than bludgeoning it into submission) but it still has all the adjustability that's needed for the majority of mastering tasks. If you like the idea of the combination of the sound of high quality analogue circuitry and the immediacy of a physical control surface, the Platinum Mix Master does the job nicely and at a surprisingly affordable price.