A stereo mastering processor that lives up to its name. Mastering is both an art and a science, with a bit of voodoo sprinkled in. Some mastering engineers

A stereo mastering processor that lives up to its name.Mastering is both an art and a science, with a bit of voodoo sprinkled in. Some mastering engineers keep their work in the digital domain, crunching numbers with computer plug-ins and avoiding unnecessary analog conversions. Others are more concerned with configuring the right analog signal chain to bring out the magic in a mix.

The latter type of engineer will appreciate Focusrite's Platinum MixMaster, with its suite of powerful analog processing tools, precision metering, and optional digital output. The end result is a multifaceted mixing and mastering processor that offers a fresh and simple alternative to the digital devices dominating the personal-studio realm.

PLUG AND PLAYThe MixMaster has an uncluttered, friendly front panel with a gleaming brushed-aluminum complexion. The processing elements - optical expander, spectral compressor, equalizer, spatial enhancer, limiter, and output control - are clearly laid out from left to right according to their order in the signal chain (see Fig. 1).

All the front-panel controls are stereo linked. Although there are no provisions for using the MixMaster as a dual-mono device, there is no reason for not using it on mono or stereo signals during tracking or mixing.

Around the back, the MixMaster offers +4 dBu balanced analog I/O on gold-plated Neutrik XLR connectors and -10 dBV balanced analog I/O on 1/4-inch TRS jacks (see Fig. 2). You can use the 1/4-inch outputs with balanced or unbalanced cables, and both sets of analog outputs are active simultaneously. The 1/4-inch inputs interrupt the XLR input jacks when both are connected.

The MixMaster also includes a pair of balanced 1/4-inch Direct Input jacks. The Direct Input signal enters the circuit just before the output-level trim control and limiter, letting you mix an external mono or stereo signal with the processed audio. Focusrite recommends using that additional input when a featured mix element, such as a lead vocal, requires a different type of processing than the primary audio source.

Above the analog I/O jacks is space for the optional digital-output card ($295). The digital card supports 16- and 24-bit word lengths and 44.1, 48, 88.2, and 96 kHz sampling rates. The connections include standard AES/EBU (XLR) and S/PDIF (RCA) output jacks as well as an external word-clock input on a BNC jack. There are switches to select the sampling rate, word length, and output, and an LED indicates when the MixMaster locks to word clock. All of these items are on the rear panel, making them difficult if not impossible to access when the unit is mounted in a rack. The review unit came without the digital-output module, so I couldn't test the MixMaster's digital capabilities.

The MixMaster runs hotter than some tube gear. Along with the rear-panel digital audio controls, that may warrant special consideration for placement in a rack.

To its credit, Focusrite goes further than most companies by making its manual a useful resource for novices. The manual includes several helpful setup ideas as well as a wealth of basic mastering tips.

DOWN THE PATHThe first effect in the MixMaster's chain is a low-threshold stereo expander optimized for suppressing audible noise at the beginning of a mix or after a fade-out. The expander has two continuously variable controls: Threshold and Release. Threshold sets the triggering level and ranges from -60 to -20 dB. Release governs the amount of time (from 0.5 to 6 seconds) it takes for the expander to fade to silence. The optical sensor used in the circuit provides smooth fades and lower noise and distortion than VCA circuits. The expander has a bypass switch and an LED ladder meter that indicates the gain reduction in 3 dB increments between 0 and -15 dB, and 5 dB increments from -15 to -30 dB.

Next in the chain is the spectral compressor, which is a stereo compressor with an optical sensor and limited multiband EQ capabilities. The bulk of this section includes standard compressor parameters. Threshold is continuously variable between -20 and +10 dB. Ratio controls the amount of compression (1.3:1, 1.7:1, 2.2:1, 3:1, 4:1, and 5:1) once the signal exceeds the Threshold setting. The Slow Attack switch offers two attack times to choose from: 10 ms when Slow is engaged and 500 s when it's disengaged.

Release governs the amount of time it takes for a compressed signal to return to its uncompressed state once it drops below the threshold. Release has four preset values (0.2, 0.4, 0.8, and 1.6 seconds) and two automatic settings labeled PDF (program-dependent fast) and PDS (program-dependent slow). Those apply varying release times to the compressed audio based on the transient characteristics of the signals occurring above the threshold. The final knob is a Make Up Gain control, which compensates for any gain reduction due to compression.

When the Lock switch is on, the compressor disregards the mix's frequency content. When the Lock switch is off, the compressor becomes frequency dependent, splitting the audio into three bands and bringing additional controls into play. Separate Low Frequency (LF) and High Frequency (HF) trim pots give you independent control over the level of the bass and treble frequencies, respectively. For example, a dominant kick drum's boom - which may trigger undue compression effects or pumping in a conventional compressor - can be trimmed so the compressor reacts less to the mix's bass range. Both controls are zero-detented and continuously variable from -10 to +10 dB.

There is no trim control for the mid-frequency compression band and no control over the crossover frequency between the high and mid bands. But the MixMaster does offer a useful low-end option with the Slope switch, which toggles the crossover point between the low and mid band to 100 or 200 Hz. In the 100 Hz position, a circuit similar to that used in the Platinum ComPounder boosts the bass below the crossover point.

Red LEDs indicate extreme compression levels (-12 dB and beyond) with lower gain-reduction values indicated in orange. A red LED above the Make Up Gain control indicates overload or clipping resulting from excessive gain boosting. The overload-threshold value is not provided in the manual, but in testing, that LED lit up when output levels approached -2 dB.

EQUALIZE ITThe MixMaster's stereo equalizer is simple and straightforward. It includes separate low frequency (LF) and high frequency (HF) shelving bands and one parametric midrange (MF) band. Available low frequency shelving bands are 40, 70, and 120 Hz; high frequency shelving bands are 10, 14, and 20 kHz. Both controls also include a Tilt setting that establishes a linear slope from 1 kHz to the extreme of the frequency range (20 Hz for the LF band, 20 kHz for the HF band), allowing broad contouring of a mix. Available gain values are 1.5, 3, 5, 8, and 10 dB of cut or boost. If you use the Tilt setting, the full gain value applies only to the top or bottom of the frequency range, causing the linear slope to pivot around the 1 kHz point.

The MF band has continuously variable Q (0.4 to 1.5) and Frequency (100 Hz to 1 kHz, with 105 switching for 1 kHz to 10 kHz), but it uses stepped gain values that match the LF and HF settings. The Frequency and Q controls have several intermediate markings around their perimeters, so you can re-create settings quickly and easily. As with the compressor, a single red LED indicates overload in the equalizer.

ON THE WAY OUTWhen the Image button in the Output section is engaged, you have control over the stereo image. The first control is a center-detented balance knob that adds up to 3 dB of level to either channel. This is perfect for correcting stereo level mismatches.

Next is the Width control, which narrows or expands the stereo image. The knob ranges from Small on the left to Wide on the right. As you turn the Width control fully counterclockwise, the circuit boosts the information common to both sides to narrow the stereo spread into a tight mono image. Turn the control clockwise toward Wide, and the differences between the channels are amplified. That increases the material unique to each channel and expands the image's apparent stereo character.

The Output Trim control is also center-detented and ranges from -6 to +6 dB. The limiter In switch engages a fixed-threshold limiter at the final analog-output stage. The meter above the switch shows the gain-reduction amount. The Effect Bypass switch at the front panel's extreme right disables the expander, compressor, equalizer, balance controls, and output trim.

The Output Meter section includes a pair of 16-segment horizontal LED arrays with overload indicators and a seven-position meter that indicates the two channels' phase relationship. You can set up the level meters to show input or output level, and they use the standard dBFS digital scale calibrated for analog interfacing so -20 dB equals 0 VU at +4 dBu. As a result, those meters have a built-in margin of safety compared with the other digital devices in my studio. A reading of 0 dB on the MixMaster corresponded to -2 dB on my Apogee PSX-100 A/D/A converter and Tascam DA-30 DAT deck.

MIXING IT UPAnyone familiar with analog audio processors and basic mastering principles will be up and running in record time with the MixMaster. With the exception of some terminology, I had no trouble using the device. The panel layout is intuitive, and the black printing, though small, is distinctly legible against the metallic background.

Focusrite's rubbery knobs are easy to grasp and spaced comfortably for large fingers. Initially, the compressor Release and EQ shelving controls were very stiff and almost impossible to turn, though they seemed to loosen up with a little exercise. Unfortunately, the knobs themselves also loosened and came off their shafts many times as a result of my labors.

In the studio, I put the MixMaster through its paces while doing rough mixes for a new CD by the Bay Area band She Mob. I also checked my findings during a premastering evaluation of finished mixes by pianist Chad Wagner's jazz trio.

I began my tests by focusing on the unit's sound and listening to determine whether it adds coloration to the audio in active and bypassed modes. I compared mixes burned directly to CD-R from analog multitrack to mixes with the MixMaster in the signal chain between the mixer and the Apogee PSX-100 converter. With all the effects individually bypassed and the global Effect Bypass switch on, the MixMaster contributed a 0.4 dB increase in gain (as measured on a digital audio workstation), with no significant timbral changes.

But when I began to add individual effects at what should have been neutral unity-gain settings, I noticed a slight drop in level. That attenuation, which occurred with the Effect Bypass disengaged, was confirmed by external metering on DAT, by the MixMaster output-level meter, and by ear. I double-checked all my settings, as well as the knob calibrations, to make sure every gain control was set to unity, all thresholds were at maximum, and the nonadjustable limiter was bypassed so that no compression was taking place. The expander seemed to be the culprit: when it was individually bypassed, there was no detectable drop in gain.

Nevertheless, there was still an audible change in the signal with the other modules switched on, notably a muffling of upper midrange and treble detail and a loss of power in the dominant distorted guitars in the test mix. Bypassing the remaining blocks one by one helped restore fullness to the mix. But even with each of the effects individually bypassed, I observed a dulling of the stereo signal when the Effect Bypass was disengaged.

On a piano trio track, switching the Effect Bypass off had a similar effect. This time, the upper harmonics of the grand piano and ride cymbal were obscured. Focusrite informed me that when all individual processing blocks are bypassed, there are still four active op amp stages between the input and output when the Effect Bypass is disengaged. Apparently, these op amps cause the coloration I heard when toggling the Effect Bypass in and out. I also heard clicks or muting of the audio when engaging the expander, compressor, spatial enhancer, and limiter; only the EQ module and the Effect Bypass were immune from annoying switching noise.

SQUEEZE AND STRETCHThe MixMaster's expander works well. The threshold range is specifically designed to minimize background noise. The quick attack time is essential to avoid losing information at the beginning of a mix. It also has ample release time to cover long fades.

Although the expander doesn't harm the mix if set correctly, it is a somewhat redundant feature, at least for any project that undergoes further computer editing or mastering.

When using the spectral compressor, I found it hard to get any appreciable multiband results at low ratio settings, such as 1.3:1 and 1.7:1. At ratios of 2.2:1 and higher, the circuit was much easier to appreciate. The LF and HF trim controls work like threshold controls for their respective frequency bands. Turning the trim clockwise resulted in less compression to the band, and counterclockwise rotation yielded more compression. Although it has no dedicated control, the mid band can be adjusted by lowering the Threshold level and raising the Trim levels.

On a grinding alt-rock number, I liked reducing the high-frequency compression; the grungy mix remained clear and unaffected in the high end, whereas the compression easily controlled the beefy guitars and bass. Turning down the HF Trim targeted the snare drum and female vocals effectively, and a little experimentation told my ears that the crossover point is around 2 to 3 kHz, a useful range for taming harsh mixes. Focusrite later confirmed that the crossover is set at 3 kHz.

I also tried boosting the low frequencies by engaging the Slope button. Although that didn't suit my rock and jazz mixes, I imagined it being useful for hip-hop and dance music. Judging by the meters, that feature also increases the amount of compression in the low and mid bands. In multiband mode, the MixMaster's compressor was responsive and musical, as well as refreshingly simple and fun to use.

In Lock mode, however - when the unit acts as a conventional single-band compressor - the effect was touchy, and it was difficult to get fluid, transparent compression. I yearned for the continuously adjustable Attack, Release, and Ratio controls found on Focusrite's Platinum ComPounder. But after some tinkering, I found low ratio settings and release times of 0.4 or 0.8 seconds added beneficial sustain to the bass range and thickened the mix.

At an overall average gain reduction of 3 to 4 dB, the snare drum was the only instrument in the mix that was noticeably compressed. Nonetheless, everything sounded great. In a number of situations, I preferred the Slow Attack mode, and I gravitated toward medium-range release times or the PDS auto-release mode in conjunction with low ratios. That kept the compressor functioning smoothly.

I drove the compressor's Make Up Gain hard to test the available headroom through the unit. It sounded great under all conditions, even when the DAT machine was pushed to its limits. The MixMaster's limiter would not distort, but at extreme levels, its obvious brickwall effect didn't exactly sound pretty. Like most VCA limiters, that feature is handy for avoiding the occasional over, but it is best used in moderation.

EQ IN SITUAlthough its single sweepable midrange band and coarse stepped-gain controls limit the EQ section, it works very well. It was easy to hear the minimum 1.5 dB changes at 40 Hz. I could even re-create the "low-end magic" trick I perform with my Focusrite Red 2 EQ by combining a low-shelving boost with a parametric cut at around 120 Hz.

Like its older sibling, the MixMaster has a comfortably wide midrange bandwidth control - one octave at its narrowest setting - which is more conducive to subtle musical results than to surgical cuts or diagnostic frequency sweeping. The 100 Hz to 10 kHz range should handle the most basic jobs, but it wouldn't hurt to have more low-end coverage as well as a tighter, more incisive bandwidth setting. Focusrite's high-shelving EQ is always extraordinarily sweet, and it's almost impossible to make it sound bad, even when reaching for extremes, such as +8 dB of high-frequency Tilt.

AT PLAY IN STEREO FIELDSThe spatial-enhancement circuit, with its Balance and Width controls, is one of those features you'll love or ignore, depending on how much tinkering you want to do with the imaging and phase relationships in a mix. I can see using it to reduce the dramatic panorama of a stereo live recording, though you could accomplish the same thing by changing the panning through two channels in a mixing board.

When I used it to widen the image of test recordings, I found the Width control usable, but only within a small range. With the Width set beyond the two o'clock position, the auditioned recordings ping-ponged or lost critical center-image information (on vocals, solos, and drums, for example), and they sounded hollow and washed out. In addition, most of the stereo mixes suffered from significant phase cancellation under extreme Width processing, taking on a disorienting quality in stereo and losing information and gain in mono.

MASTER STROKEFocusrite's Web site says that the MixMaster is "designed primarily for project studio mastering," and I can't argue with that. The operation's simplicity and carefully chosen features offer a lot of processing power for much less than what a rack of mastering-grade equalizers and dynamics processors would cost.

Unfortunately, because of noticeable coloration and switching noise in the unit, I wouldn't recommend the MixMaster for mastering in professional facilities above the personal-studio level. When implementing dramatic changes in timbre and gain, or for "set it and forget it" processing, you can dismiss such problems as only minor limitations. But in situations where mixing or mastering decisions are based on critical A/B comparisons, transparency at unity gain and noise-free operation are minimal requirements of any mastering device, regardless of price.

The MixMaster's equalization and compression circuits descend from some of the best analog gear made, and they sound great despite the unit's shortcomings. Don't reserve those effects for only the final mix; they're invaluable throughout the recording process, including tracking, stereo recording, and single-channel processing. For its EQ and compressor alone, the MixMaster is worth its sticker price, and the additional effects are a welcome bonus.