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Symetrix 551E

5-band Parametric Equaliser By Paul White
Published December 1997

Symetrix 551E

For serious sonic sculpting, you can't beat a parametric EQ, and this new contender from Seattle‑based Symetrix is priced within reach of many project studio owners.

As most of you will have discovered, the EQ section on a typical mid‑price console has its limitations — if you do a lot of boosting using a budget desk EQ, the results will probably sound unnatural in some way, often taking on boxy or nasal overtones. So for serious tonal bending you'll need to patch in a high‑quality outboard equaliser.

The majority of high‑end equalisers follow the parametric format, simply because parametric EQs are more flexible than any other type, and as a rule, the more bands you have, the more overall control is possible. The downside of the parametric EQ is that it can be quite a difficult beast to set up, especially for inexperienced users, but providing you start out using only a couple of bands at once, it shouldn't take too much getting used to, and the benefits are very worthwhile. For those unused to parametric EQs, you can think of them as being similar to graphic equalisers with just four or five bands, but where each band may be set to any frequency, and where the width of each band may also be adjusted.

Considering the number of compressors and gates on the market priced to appeal to private users, there are relatively few similarly priced parametric equalisers, but Seattle‑based Symetrix has just added a new model to the list. Conceptually, the Symetrix 551E is a very simple, single‑channel device providing five identical bands of EQ. Each band has a three‑way selector switch and a Frequency control enabling it to cover the entire audio spectrum. Connection to the unit is via either balanced XLR or balanced jacks, and — unusually for a unit of this price — the output stages are servo balanced and DC coupled (the input stages are also DC coupled), to maximise low‑frequency response and to avoid the introduction of undesirable phase shifts.

Packaged in the familiar 1U‑high rackmount case and finished in the relatively new dark blue Symetrix livery, the 551E has an internal mains power supply connected via a standard removable EC mains lead. The audio jacks and XLRs are wired to AES specifications and are located on the rear panel. Symetrix describe their filter design as 'UltraQ', a circuit created to deliver very low‑noise performance, though no circuit diagram is provided to satisfy the curiosity of those interested in technical details.

On the front panel are the five identical filter sections plus a high‑/low‑cut filter that allows independent control over the frequencies of separate low‑pass and high‑pass, 12dB‑per‑octave filters. The low‑pass filter can be swept from 3kHz to 65kHz and the high‑pass from 6Hz to 260Hz. There's also an input level control (+/‑15dB range), with clip LED, and a bypass button that operates a hard bypass relay, taking both the parametric and high/low equalisers out of circuit. In the event of a power failure or PSU fault, the input is routed directly to the output. The clip LED monitors the signal post EQ so that any overload caused by excessive boosting is detected.

Parametric Stages

Each of the five parametric stages is absolutely identical, each having a frequency control knob calibrated from 100Hz to 2kHz. The reason all five bands have the same range is so that there are no restrictions on whereabouts in the audio spectrum the various bands can be used. For example, it's possible you may want to use three or more bands just to sort out problems at the bass end. Each parametric stage also has a 3‑way toggle switch that can either multiply or divide this range by 10. The switch positions go in the order x1, x10, x0.1, which may not seem entirely logical, but the manual points out that there's no way to wire a conventional toggle switch so that it works in the desired order. Doubtless there are ways around this, but at a cost out of all proportion to the benefits. Combining the three switch positions with the variable frequency control provides a total coverage of 10Hz to 20kHz — though some users of esoteric equalisers claim there is a benefit to be had from enabling the user to boost up to 30kHz or beyond. However, the audio bandwidth of the basic circuitry is from 20Hz to 63kHz, with the signal being only 3dB down at 63kHz.

The reason all five bands have the same range is so that there are no restrictions on whereabouts in the audio spectrum the various bands can be used.

The filter bandwidth control is calibrated in octaves rather than the less intuitive Q, and is adjustable from 0.05 to 2, while the cut/boost control allows up to 12dB of boost and a usefully high 20dB of cut. I've often wondered why manufacturers don't tend to build equalisers with more cut than boost, as you invariably need more range when cutting than when boosting. Now someone has! Unfortunately, there's no separate bypass for each band, which can make setting up trickier than usual for the inexperienced user. There's also no facility for splitting the EQ into two groups for stereo use; presumably this is because the 551E has an odd number of bands.

Using The 551E

Setting up the 551E is exactly the same as setting up any other parametric EQ, but because the knobs are quite small in diameter the adjustment feels rather coarser than it would if large knobs were used on exactly the same equaliser. (Actually, I've often suspected that some vintage gear is claimed to have a nice feel purely because of the larger‑diameter controls.) Having the high‑ and low‑pass filters in addition to the five bands of parametric EQ is a big bonus, as they make it very easy to 'bracket' a specific part of the audio spectrum for the surgical removal of unwanted high end or low end. These filters work in much the same way as the side‑chain filters on a Drawmer DS201 gate, and they'll often solve a problem that takes a considerable amount of work with conventional EQ.

Listening to the parametric sections shows them to be very quiet and positive, though they tend to lack the enigmatic, silky top‑end magic of the really good (and really expensive) models. Even so, this equaliser is hugely more useful than a typical desk EQ and it's simple work to kill an over‑prominent resonance or to lift out a hi‑hat. What is particularly instructive is adding boost right at the limit of human hearing, because there's no doubt that it makes a difference to the part of the spectrum you can hear, generally improving the detail and transparency of the mix. It would have been interesting to see what effects were possible had the EQ range been extended to 30kHz.


The 551E is designed as an affordable workhorse of an equaliser, yet its technical performance is actually very good, and five bands provides as much scope for creative or corrective work as most people can handle. I like the fact that all the bands are fully tunable over the whole audio range, I like the variable‑frequency high‑pass and low‑pass filters, and I think the relay bypass is a good idea, especially for use in live situations, where loss of signal under fault conditions is not an acceptable option.

If there's a criticism, it is that each band should have its own bypass button — setting up without this facility is less straightforward. It's also a pity that you can't use the unit as a 2‑channel, 2‑band processor, even if it would mean making one of the bands and the high‑/low‑pass filters redundant in stereo mode. Extra sockets allowing the high‑/low‑pass filters to be used independently of the rest of the equaliser would also have been useful, but you can't have all your wishes without increasing the cost.

As it stands, this is a very competent and well specified equaliser that strikes a good balance between performance and price.

EQ Rules Ok

The manual for the 551E offers a brief but comprehensive introduction to using a parametric equaliser, and points out that, because of the way the human hearing system works, cutting frequencies tends to be less noticeable than boosting when it comes to undesirable side effects. As a very general rule, use wider bandwidths and smaller amounts of boost when boosting frequencies and narrow, deeper notches when cutting. Finding the appropriate frequency for cutting or boosting is usually easiest if you set the equaliser to maximum boost, then sweep through the spectrum until you locate the frequency that needs adjusting. Once this is located, the cut/boost control can be reset to a more sensible value.

As with the vast majority of outboard equipment (other than mic preamps), the 551E is designed to work at line‑level signals and will not accept a microphone plugged in directly. Equalisers are normally connected via mixer insert points or patched directly between two other pieces of equipment in the audio chain.


  • Five full‑range bands.
  • Variable high‑ and low‑pass filter included.
  • Relay hard bypass.
  • Good technical performance.


  • No stereo split facility.
  • No individual band bypass switches.


A well‑designed workhorse equaliser with lots of range, plus the benefits of variable high‑ and low‑pass filters.