SPL Machine Head Digital Processor

The German company SPL Electronics is relatively unknown in the U.S., but it has a new friend here, for I've found a box that produces a very special sound quality.
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The German company SPL Electronics is relatively unknown in the U.S., but it has a new friend here, for I've found a box that produces a very special sound quality.
Product PointsApplications: Mastering studios

Key Features:
Generates analog tape saturation effects in the digital domain; AES/EBU or S/PDIF 24-bit I/O


SPL Electronics at 718-963-2777


+ Get that great fat "analog" sound from all-digital sources

+ 24-bit in and out

+ Habit-forming


- Only basic MIDI control functions, no SYSEX

- Memory save/recall ergonomics a bit awkward

- Sound becomes a bit grungy with high drive/signal levels

The Score: An essential new mastering tool that's easy to use and understand. Supplies the missing link in many all-digital recordings.
I should start at the beginning: Forbidden Records' recent release, alternative rock band Real Cool Traders, was mixed to DAT from ADAT master in a project studio. This gave the band and the producer the luxury to fine-tune the performance and produce a great mix. They did everything right, including having the mastering engineer (me) consult on the preliminary mixes. Then it was up to me to bring home the bacon.

My first draft master sounded good. It was punchy and clean, perhaps even overclean, but it lacked a certain fatness that was in previous works I'd mastered for this record company. The reason: previous works had been recorded and mixed on analog tape (at my urging); I'd dubbed Mike Gibbins' (of Badfinger) DAT to 1/2" analog and back to 20-bit digital. But I felt that Traders would go downhill if dubbed to analog, because every time I dub to analog, the bass gets looser, and this album could not afford a looser bass sound. I had to preserve or enhance their sound, not take anything away. In effect, I needed the sound of analog tape without going to tape!

I told them the problem was that Traders was an all-digital project. Digital recording is often inappropriate for rock and roll - it's a bit too dry and uncolored (for want of a better word); 16-bit DAT is also less resolved than analog, which increases the dryness and harshness.

I tried everything to duplicate that fat analog sound, from specialized compression and other dynamics processing to some proprietary tricks, but nothing came close. Fortunately, I've been doing some searching on the Net, and Hermann Gier, managing director of SPL in Germany, told me about Spectral Design's digital tape saturation algorithm, a DAW plug-in marketed by Steinberg, and also available as a standalone rack unit from its hardware partner, SPL Electronics.


The product, called the SPL Machine Head, is a 24-bit processor with digital connections only. Gier reported that it duplicates the distortion characteristics of analog tape without the downside (no wow, no flutter, no tape hiss). I located the U.S. distributor, crossed my fingers and ordered a unit for evaluation to see if it would do the trick.

Some trick it is! The Machine Head is a heavy-duty 1 rackspace box with a distinctive orange-red front panel. Rear connectors include 24-bit S/PDIF and AES/EBU. When power is turned off, a hardwire relay connects input to output; very useful for system debugging. Word clock in and through with termination switch, MIDI and RS-232/422 for software updating.

It's a cinch to operate - four rotary knobs act in analog fashion, exactly the way one uses a tape recorder, except that an LCD displays the knob's values (better than analog tape!). Input gain should normally be left at unity, unless the processor is clipped with extreme settings, or the source is at low level. Of course an all-digital source will never be too high.

Drive is equivalent to record level calibration, like setting up a tape recorder for elevated level. Except, one turns up the drive (in 1/10 dB steps) and simply listens until exactly the degree of saturation (or fatness) desired is reached - a lot easier than analog.

It helps to turn the output gain down to audition at equivalent loudness, similar to the playback-level calibration of an analog recorder. If the user boosts the drive by 5 dB, output only has to be reduced by 4.5 to restore subjective unity gain, demonstrating saturation in action. After making the comparisons, turn the output gain up until it's just below clipping. Built-in meters and clipping indicators aid in this process.

The last knob is HF-adjust, which controls the amount of high-frequency damping in 1 dB steps. It's reported to vary the amount of high-frequency vs. low-frequency saturation. To my ears, the HF control's turnover frequency is a bit too low or its Q too high; more than 1 dB of boost exaggerates the upper midrange frequencies instead of the more-desirable extremes. If more than 1 dB of HF boost is needed, I would not do it in the Machine Head.

In use

Placed in my processing chain, the Machine Head helped give Traders exactly the sound we were looking for. When combined with all my other processing, the sound was literally jaw-dropping. I was able to use much less equalization, sibilance control and even less dynamics processing.

The warm harmonic distortion of the Machine Head added fatness and fullness to the bass, guitars and drums, presence to the vocals. An apparent high-frequency saturation reduced vocal sibilance, made the cymbals sound more real and removed a certain fatiguing edge. It really was remarkable to hear it work. Digital processors have come a long way.

Later projects have confirmed the MachineHead'spower. On an all-digital recording by a solo artist, the SPL Machine Head made the sound more organic, reducing its sterile dryness. Not all digital recordings have these problems, but who would have thought that distortion could improve a recording?

I obtained a significant loudness gain of 5 dB or more from a relatively uncompressed source. This will vary depending on the musical source and drive level - higher drive yields more subjective loudness. My settings resulted in a peak-to-average ratio of 14 dB, which emulates a not-too-saturated 30 IPS analog tape.

Remarkably, this peak level decrease was obtained without any scrunching, pumping or other effects normally associated with compressors, since most of the compression was obtained by filling in the holes with harmonics. Think of it as a compressor without the artifacts of attack and release times. With moderate drive settings, the music actually sounded more dynamic. As drive is increased, musical dynamics are too compressed, and unless you're looking for that sound, you know you've gone too far.

Other controls include a tape speed button that alternates between virtual 15 and 30 IPS. Though the difference was subtle, I definitely preferred 30, as I felt the HF losses too much at 15 with this particular material. This analog simulation is so realistic that I speculate they're emulating IEC instead of NAB curve.

An active button engages or bypasses the processing. Four preset buttons allow saving up to 99 user presets and switching either manually or via MIDI program changes. I had no need for MIDI on this project, but would welcome automation if songs come from different sources. I regret the active function is not automated, because some songs might come from analog tape and not need processing. Gier informed me that a drive level of -7 is equivalent to off, so I could automate bypass that way.

Current software version is 1.1. With no provision for naming presets or doing a Sysex dump, be sure to keep a log of each project; this is an alarming omission for a product in this price range. Comparing presets requires several awkward button pushes (part of a safety routine to protect and inspect register contents) but one can easily compare presets with a MIDI controller. Once I became familiar with the Machine Head's sound, I found less need to compare presets, and simply tweaked the parameters until I liked the sound. All presets are preserved if power is lost.


Warning! This box is habit-forming. If you're the type who puts salt on your food before tasting it, don't buy this box; or maybe you should if your clients like impetuous taste. There's a definite learning curve, and like all effects boxes, you will probably end up using less effect after acclimatizing to the sound. The drive control varies the sound from a pleasant fuzz to subtly fat to nicely full, then fuzzy but good, next, a bit grungy, but nice edge and finally overblown and saturated. At the extreme, it even produces some of that flubbery bass quality you get with an overloaded analog tape. Very desirable for some kinds of music!

But use it with a decided goal. For Real Cool Traders, we desired that alternative-rock-slightly-bright-grunge sound, and got it very easily with the Machine Head. But this effect was entirely level-dependent, and the soft passages still sounded pure and warm. This box does not emulate the image phaseyness of analog tape, which often produces a desirable sense of depth. But I have other tools that can alter image, depth and the ambient soundfield, so I didn't miss that particular analog effect.

When evaluating the Head, be careful to compare active to bypassed at equal loudness. The loudness gain of this unit is astounding, but when the output gain is readjusted to produce equal loudness when bypassed, the sound difference is much more subtle, like comparing the console to the output of a good 30 IPS tape deck. And it makes most digitally recorded pop music sound better, it's only a matter of deciding how much effect you want.

Let's put the sound of this box in perspective. It's not a substitute for a great engineer, mix console, outboard gear and well-aligned 30 IPS analog tape. That combination is more resolved, transparent and warm, and relatively little is lost when dubbed through a good 20/24-bit A/D at the mastering studio.

I think the Machine Head should be reserved for the mastering studio, but it can be used in mixing, particularly between a digital mix console and a 24-bit digital recorder. Like most good effects, a little Machine Head goes a long way. I suggest a high-resolution, high-headroom mix/monitoring environment that you are totally familiar with - like a good mastering studio. Soundwise, as the Cheerios ad says - the Machine Head tastes wonderful and is very nutritious when "part of this complete breakfast." When all was said and done, I couldn't part with my evaluation unit and just had to buy it. My clients would insist.