There are some equalisation tasks for which only a parametric design will do the job. The PE-40 features no fewer than four independent equalisers, each having four true parametric filter sections.

When it comes to parametric equalisation, there's still a certain amount of confusion as to what the term actually means. It is all to often applied incorrectly to sweep equaliser designs. A true parametric design has three controls per filter section: Frequency, Bandwidth or Q and Gain. As with a sweep system, the Frequency control is used to tune the filter to the frequency that you wish to treat and the Gain control then used to apply cut or boost at that frequency. However, the extra Bandwidth control means that you can set the filter to work on a very narrow range of frequencies or on a broad one as required. For example; if you have a signal that is good but contains an annoying amount of mains hum, you could tune in the filter to 50 or 100Hz depending on where the hum is worst, cut that frequency to reduce the hum, and set a narrow bandwidth so that the frequencies to either side of the trouble spot are affected as little as possible.

On the other hand, if you are using the filter as a sophisticated tone control, you will find that a narrow bandwidth sounds peaky and unnatural and so should be readjusted for the best results.

Construction

This is a 2U rack mounting device, though the rack mounting ears come as optional extras, and is built to the high standard that we have come to expect from Tascam. All the connectors are on the rear panel in the form of phonos and all the controls are on the front panel which is finished in gun-metal grey with white Legend. The power switch and red status LED are located on the left hand end of the front panel and all four sets of filters are identical. Each filter set contains four filters wired in cascade so that the input passes through all of them and a bypass switch allows instant comparisons to be made without resetting the controls. Each of the four filters within each group is dedicated to a particular section of the audio band and the controls are colour-coded for ease of operation, but there is some overlap. The ranges are as follows: 40Hz to 800Hz (green), 200Hz to 4kHz (orange), 500Hz to 10kHz (blue), and 800Hz to 16kHz (red). The gain control allows a cut or boost of 15dB to be applied and as previously mentioned, the Q control sets the bandwidth of the filter. To save panel space, the Q knob and the frequency knob are in the form of a dual concentric control, the Frequency part being in the centre. In addition to the parametric filters, each of the four groups has a switchable high and low-pass filter for additional flexibility. The high pass is really two filters. These are 160Hz/6dB per octave and 60Hz at 18dB per octave and the switching arrangement lets you select either, neither or both. These filters are handy for eliminating low frequency rumbles or boom and will be welcome both in the studio and in PA work. The low pass filter is simply on or off and acts at 15kHz with a response of 12dB per octave.

Turning now to the back panel, it can be seen that there are Auxiliary and Foldback outputs in addition to signal In and Outs. The Foldback output passes the unequalised sound back out of the unit so this is in effect the same as the input. Looking at the circuit diagram shows that the Input and Foldback sockets are indeed linked together so the Foldback output is not buffered. Similarly the Out and Aux sockets are electrically commoned. The nominal input working level is -10dB (0.3v), though the circuit will accept levels of up to +18dB. The output levels are identical so it can be seen that you will need to keep the input level to -10dB if you're not going to run out of headroom when applying large amounts of boost, particularly if you set two of the filters to nearly the same frequency.

"...each group of filters has only one Bypass switch so you can't set up one filter section at a time and listen to its effect in isolation. This could be a real limitation..."

In Use

In common with most parametric equalisers, this design uses fairly conventional state variable amplifier circuitry and functions well. You do however have to think a little bit about using such equalisers and the best way to set them up seems to be to apply full boost on the gain control and then tune in to the problem area using your ears as a guide. Once the correct frequency has been located, it should be easy to modify the bandwidth and gain until the desired result has been achieved. The only real problem with this is that each group of filters has only one Bypass switch so you can't set up one filter section at a time and listen to its effect in isolation. This could be a real limitation if you are using significant amounts of cut or boost on all four sections. Another small problem is to do with the ergonomics of the device: principally the pot spacing which is rather tight when you're trying to adjust the Q on the dual concentric control. I notice that there is about an inch to spare on the right of the front panel, and this space might have been put to more profitable use by spreading out the controls a little. A small point perhaps, but as this is one of those units that, once purchased, you wonder how you ever did without it, and the consistent jamming of fingers could prove annoying.

People often complain that equalising the top end of a signal makes it more noisy but that is inevitable to some extent. Obviously when you boost a certain frequency, you are turning up the gain in that area of the spectrum and so any noise present in the input in that same area will also be increased by the same amount. I find that parametrics are more useful for severely cutting frequencies rather than boosting them and that for tonal modification, only small amounts of boost are needed. Having several filters in one bank is particularly handy in cutting the effect of hum but to this end, it would have been more useful if the second filter bank could be swept down to 100Hz allowing you to cut at both 50Hz and 100Hz as hum has significant components at both these frequencies.

The instruments that usually benefit from a small amount of boost are bass drums, when they need to be more punchy, and snare drums, when you want to give them a bit more crack. As drums are more often than not recorded first it's sometimes hard to envisage what the sound should be before the rest of the instruments have been put down, and a parametric often comes in useful later for those minor but crucial alterations which only such a versatile unit can execute.

"Having four sections means that even with a fairly modest desk, you're not going to find many EQ situations with which you are unable to cope."

Conclusions

A flexible EQ system such as this one is a valuable addition to any recording or PA set-up as most budget mixing desks leave you with parts of the frequency spectrum that you can't treat without severely changing everything else in the vicinity, particularly in the lower mid-range. Having four sections means that even with a fairly modest desk, you're not going to find many EQ situations with which you are unable to cope.

Fitting separate bypass switches to each filter section would have made setting up a lot easier, especially for the user who lacks experience in using parametrics, and Tascam ought to consider this move if they come up with a new version. Also an overload LED wouldn't go amiss to let you know if you'd boosted any frequency so much that it was in danger of clipping. Those criticisms aside, this is a useful piece of gear and, though it may not be as romantic as the latest in digital reverbs, it can make a lot of difference to the quality of your recordings.

The Tascam PE-40 has a retail price of £425.50 including VAT and further information can be obtained from Harman UK Ltd, Professional Products Division, (Contact Details).