For a long time equalisation was looked upon as a form of tonal correction for deficiencies created by sound equipment. It was only in the seventies that recording engineers/producers really accepted the fact that equalisers had a 'creative' function as well as a 'corrective' one, and this acceptance subsequently helped lead to the availability of 'stand alone' equalisation units both for recording and live performance applications.

Basically, there are two types of equaliser available: Graphics divide the audio bandwidth into discrete frequency bands, the number and spacing of which are determined by the cost. Generally speaking, the more bands the better. The spacing between the bands is described in part octaves - half, third and full octave being by far the commonest type. Each band features its own cut and boost control for altering the level of frequencies (sound) controlled by that slider, and the position of each slider creates a 'graphic' display of the way the sound is being tonally modified - hence the name.

The important difference between a graphic and a parametric equaliser is that graphics have fixed frequency bands, but many of them. Parametrics on the other hand have variable frequencies, and can be swept over wider ranges, but are only commercially available with one or two individual frequency bands as the norm.

Controls

The 1140 Parametric EQ/Preamplifier from Danish manufacturers TC Electronics offers four such bands in a single, mono unit that is aimed at both professional and semi-pro users. The unit comes in a sleek 1U high, 19" rackmounting case and is finished in black. All controls are sited on the front panel which is well laid out for ease of operation. The four frequency bands each have three controls labelled 'Centre', 'Bandwidth' and 'Function'. 'Centre' sets the frequency you wish to control, the range of which differs on each band. The available ranges are as follows: Centre (1) 20-2kHz, (2) 50-5kHz, (3) 100-10kHz and (4) 200-20kHz. As can be seen, this means that all four bands overlap, which is necessary if you really want to hone in on several frequencies within a small range (say, between 1 and 3kHz). It also means that all four bands cover the all important midrange region from 200-2kHz. A very useful feature.

'Function' determines the amount of signal cut or boost there will be at the frequency set by the Centre control, and a massive 20dB of gain or attenuation is possible, enough to virtually mute all signal output if all four bands have wide band-widths and full cut applied. Talking of bandwidth, this is the last of the three controls. Using this knob you can increase or decrease the number of frequencies (either side of the centre frequency) that will be affected by the action of the Function control. The number of frequencies (bandwidth) is adjustable over a 6½ octave range - from 0.1 to 2 octaves, which is wide compared to most parametric units on the market.

This then is the beauty of the parametric, as the combination of the Centre and Bandwidth controls means that you can 'tune' the device to accurately cut out a single frequency, say 5kHz, without affecting the overall sound drastically. Alternatively you can have a wide bandwidth and small amount of boost or cut, and gently modify a specific area of the sound such as the bass or treble regions, in much the same way as with the simple tone controls on your radio or hi-fi. The choice is yours, and with four sets of controls at your fingertips the tonal variations are virtually infinite.

The remaining front panel controls are concerned with input/output levels. 'Input Gain' provides plus or minus 20dB of input signal adjustment, the maximum levels being +22dBm and +6dBm for high and low level signals respectively. Output is used to maintain the maximum signal-to-noise ratio possible, and controls the overall output level.

The 'EQ Match' control is a useful feature that lets you balance the normal and effected signal levels. A necessary +/-16dB of adjustment is provided as, essentially, what you are doing when cutting or boosting signals with a parametric is increasing the volume of certain frequencies. Heavy boosting often leads to distortion as there is insufficient signal 'headroom' available from the unit ie. it cannot handle the increased signal levels. What the EQ Match knob allows you to do is reduce the average level of the signals to a low enough degree, so that the maximum 20dB of boost you may have applied does not cause distortion. The reverse operation is required when attenuating signals in order to avoid their being lost in background noise.

To aid you in these operations there is a neat, 5 segment PPM meter of the LED ladder variety situated above the Bypass switch. Calibrated from -20 to +3dB the readout changes colour (green, amber, red) to indicate the increasing signal level. In addition, there are separate red 'overload' LEDs above each frequency band that light up 6dB below the onset of 'clipping', which is quite easy to induce if careless with the EQ boost.

The front panel is completed by the 'Bypass' switch. This is the non-latching MOSFET variety with silent operation. Pressing this down switches the equalisation in or out of circuit, depending on which mode the device was in originally. A rear panel jack socket connection for a footswitch duplicates this function, for remote switching if required.

Rear Panel

The rear panel sports both balanced and unbalanced signal connections. XLR type male and female latching sockets are used for the balanced output and input, with impedances of 50 ohms and 20 kilohms respectively, whilst Preamp Input and Output use standard ¼" jack-sockets. Unfortunately, there is no mains switch which is a dangerous omission (you simply plug the unit into the mains to turn it on) but there is a detachable Euroconnector.

Conclusions

This is a very good unit, robustly designed and very easy to operate, if you know what you are doing, as there is always the temptation with parametric EQ to boost signals for the hell of it. With the 20dB gain available from this unit, overzealous equalisation can easily lead to blown monitor speakers, 'ringing' ears and distortion - so be warned! Used tastefully, this unit can be so effective and an ideal addition to any recording set-up. If you have a mixing desk with poor EQ then one of these units patched into an auxiliary send/return chain will open up a new world for you. All in all, a thoroughly professional unit at a semi-professional price; the only real criticism is the lack of separate EQ bypass switches for each individual frequency band. Still, this unit represents extremely good value for money, and should be looked at closely by anybody considering purchasing outboard equalisation.

The TC 1140 Para EQ retails at £188.60 inc VAT and is distributed in the UK by MTR Ltd., (Contact Details).