Aimed at the serious semi-pro enthusiast, this unit combines a compressor limiter, a 18 band graphic EQ and a pair of tunable notch filters, all of which may be used separately or in combination.

The role of the graphic equaliser and the compressor/limiter has been well documented in the pages of HSR but the notch filter is probably a bit unfamiliar to some of you so I'll go through this section first.

Notch Filter

A notch filter is a narrow band tuned filter which, like a sweep equaliser, may be set to cover a large proportion of the audio range. Once set to a specific frequency however, the amplitude (volume level) within this band may only be cut, not boosted as would be possible with a conventional sweep EQ circuit.

Though notch filters can be used for creative EQ, their main purpose is a corrective one. If the bandwidth of the filter is made fairly narrow, a section of the frequency spectrum may be almost entirely removed without having much effect on the overall sound and this technique is particularly useful for removing or attenuating mains hum or the buzz caused by fluorescent lights.

Likewise, if an instrument that you have recorded has an annoying peakiness, this can be tamed by careful use of a notch filter.

The filter provided on this unit is in two sections, one covering the range 50Hz to 800Hz and the other covering 500Hz to 8kHz. Both sections may be continuously tuned over their operating range and the amount of cut may be varied from zero to -30dB which is quite a severe cut when set to maximum.

All the processors, including the notch filter, may be switched in or out of circuit by means of a front panel pushbutton switch accompanied by a status LED.

Graphic EQ

This is a fifteen band device and covers the frequency range 25Hz to 16kHz in steps of two thirds of an octave. Each band slider has a centre detent for accurate centering and an additional button sets the maximum signal cut or boost to either 12dB or 6dB. Again there is a bypass switch and a peak LED is fitted to indicate an overload which would cause distortion.

The EQ circuit is of the inductorless gyrator design and this type works well providing that adjacent channels are not set to widely different levels of cut or boost which in normal use, they would not be.

A fifteen band graphic is a useful tool for corrective or creative equalisation and the number of bands means that quite detailed adjustments can be made.

Compressor/Limiter

These are used to restrict the dynamic range of a signal and typical applications would include levelling a vocal track or taming an uneven bass guitar.

It is sometimes necessary to use a pair of limiters to prevent the levels from a stereo mix exceeding a certain volume and a similar principle is often used in PA work to avoid power amplifier clipping but here, the single unit would normally be used to treat one voice or instrument.

The first control in this, section is the threshold; this sets the level at which compression starts to take place and below that level, there is no effect on the signal.

Once a signal exceeds the threshold, the circuitry turns down the gain in order to keep it under control and the amount of gain reduction is indicated by a seven segment LED ladder so that you can always see just what is going on.

The actual amount of gain reduction is set by means of the ratio control, the limits being from 1:1 (unity) and infinity to one. In practice, this means that the range can be set so low that, once the threshold is exceeded, no compression at all takes effect. On the other hand, with the ratio set to infinity, the output level can never rise above the threshold level and, used in this mode, the effect is called 'limiting'.

Compression is obtained by using a ratio somewhere between the two extremes and, unless you wish to create a special effect, it is wise to use no larger compression ratio than is strictly necessary, otherwise undesirable side effects may start to creep in.

A full spec studio compressor has variable attack and release times but this unit is preset to a compromise set of values and how well this works, you can read later.

Construction

Before looking further at how the unit performs, let's take a look at how it's put together.

The control layout can be seen from the photograph and, as you can probably see, the case is of the 19 inch 1U format.

For those of you reading in black and white, the front panel is a sort of platinum blonde anodised finish as are the control knobs, the rest of the case being the usual satin black.

The rack-mounting brackets are detachable if required, but I can't really see anyone bothering to take them off. All the connections are on the rear panel and these are wired to permit the use of balanced or unbalanced inputs and outputs though standard mono jack inputs may also be used.

The effects are 'normalised' so that if you put your input into the limiter and take an output from the notch filter, the three processors are connected in series. Each section, however, has its own input and output socket and plugging into these will isolate any individual processor by breaking the signal chain. This is a useful feature as there are many applications where two or three sections would be used together to process one signal path.

In Use

The processors were tried individually and in combination, the results being as follows.

Firstly the compressor/limiter; given that there is no manual adjustment for attack or release time, the preset values appear to be a very good compromise. On instruments or vocals, the compression can be set to keep a check on levels without making its presence felt providing that no more compression is applied than is needed. The LED ladder proved invaluable in setting the threshold control and I tended to set things so that an average level illuminates only one section of the meter, indicating that gain reduction is only just starting to take place. Choosing a ratio of around 3:1 will then keep signal peaks in check but will not totally destroy the dynamics of the input.

This process really helps to keep vocals above water in a mix and can make a distorted guitar sound subjectively louder without any real increase in overall level. The bypass switches do not seem to cause any audible clicks but it is unlikely that these will be used during a normal recording or mix-down; still it's nice to know that you can if you want to.

Graphic Art

Most graphics just do their job with no fuss and this one is no exception. Fifteen bands is a useful number to have and it is possible to emphasise or cut various parts of the spectrum as well as trimming off bits that aren't used by a particular instrument in order to remove excess noise or crosstalk. This is especially useful on lead guitar where not much happens below 100Hz and so the bottom sliders can be pulled down to cut hum or cross talk from a recorded bass guitar.

The overload indicator is a good feature and it enables an optimum signal-to-noise ratio to be achieved by ensuring appropriate level matching. To set the compressor/limiter output level, just increase the gain until the overload LED on the graphic blinks on loud sections. All you have to do then is back off the gain a bit and you're there.

Top Notch

The notch filters really do operate over narrow bandwidths and so side effects are minimal. Providing that the signal you are trying to cut is also narrow band, things are fine; but if it covers a wide range, the filters will make very little impression on it.

Generally, notch filters are used to reduce mains hum which this one will do but remember, mains hum generally has harmonics too and so you can only tune out the fundamental 50Hz or 100Hz component; the harmonics will remain.

Still it's a useful tool to have at your disposal, mainly for salvage work!

Conclusions

It would be easy to say, "Wouldn't it be nice if the limiter had variable attack and release controls" or "I wish the notch filters had variable bandwidth or were fully parametric", but on a unit of this size and price (£369), you have to call a halt to the facilities somewhere.

What you do get works very well and very quietly and for the home recording market, it is a very useful new piece of gear. You can thicken vocals, strengthen instrumental tracks, and the graphic will let you get to those parts that the EQ section of your mixer just can't reach. I like it!

The MSP1000 has a recommended selling price of £369 inc VAT.

Further details from UK distributors Summerfields, (Contact Details).