Once you've bought your recorder, mixer and monitoring system, a good compressor should be near the top of your outboard equipment shopping list. This dual channel unit from Yamaha offers all the facilities that you might expect from a fully professional unit including a low level expander gate.

If you are in the business of recording purely electronic instruments, then it is just possible that you could get through life without ever needing to use a compressor. Most of you however, will mike up the occasional instrument or vocalist and it is in this area that a compressor is indispensable.

Compressors fall into the category of signal processing equipment that can be used in both corrective and creative situations, so it is worth touching on these areas before continuing. As regular HSR readers will know, a compressor is basically a device which reduces the dynamic range of a signal, the overall effect being to reduce fluctuations in the level of that signal. Probably the main corrective use of a compressor, at least for the home recordist, is to stabilise fluctuations on a vocal track caused by a combination of poor mic technique and the natural dynamics of the vocalist.

If correctly used, a compressor will help the vocals to sit correctly in the track, whilst still retaining a constant perspective: the same track without compression may well see the vocals disappearing and reappearing like the head of a drowning man in a choppy sea. By varying the compression ratio, the amount of signal appearing at the output can be made to vary more or less for a given change in output signal. At maximum compression, the output is effectively prevented from rising above a set level and this is known as limiting. Rather than being used for an effect, limiting is often used as an electronic safety net to prevent transients from overloading pieces of equipment further along the audio chain (such as reverbs, power amplifiers or radio transmitters).

The compression ratio itself refers to the change in input level (in dB) that will bring about a 1 dB change in output level, so no compression at all corresponds to a compression ratio of one to one, whilst true limiting would require a ratio of infinity to one.

Construction

The 1U rack case housing this unit is elegantly finished in black satin paintwork with a gold legend. Physically, it matches the style of other Yamaha processors, being both smart and ergonomically laid out. Both compressors may be operated independently or ganged for stereo operation and links on the rear panel allow the control circuitry to be fed from an external signal source so that the level of one signal may be controlled by another. Useful applications of this facility include 'ducking' where a voiceover automatically turns down the background music or solo emphasis where for example, a lead guitar part can be made to stand out from the mix by automatically lowering the level of the backing tack.

Also on the rear panel are the unbalanced inputs and output which are available on both jack and phono sockets.

Controls

The front panel line drawing shows where everything is physically located and from this it can be seen that each channel has its own bypass switch. This however does not disengage the expander gate facility so by turning the compressor switch to 'out', the channel may be used purely as a noise gate if required.

Input and output gain controls are provided - essential if the unit is to be compatible with all the common signal level formats as these range from -10dBm to +4dBm; even some semi-pro mixers such as the Allen and Heath System 8 range would appear to use +4dBm at the insert points.

The threshold control selects the level below which no compression takes place whilst the ratio control allows the compression ratio to be varied continuously between one-to-one and infinity-to-one. Attack and release time controls are both fitted, giving a range from 0.2 to 20ms and 0.05 to 2 seconds respectively, and the expander gate uses a single threshold control. Its circuitry has a preset attack and release time and a status LED indicates when the gate is functioning.

In order that the operator knows just how much gain reduction is taking place, a five section LED ladder meter on each channel displays this information up to a maximum of 24dB gain reduction.

Link

With the unit switched to linked or stereo operation, it is important to know which controls still work, and which have been overridden. The lowest expander gate, attack and release settings take priority over both channels whilst the highest threshold level takes precedence. The input and compression ratio controls must be set manually to the same settings, because otherwise the stereo imaging will shift alarmingly, (though I suppose this could constitute the basis of a novel special effect).

In Use

On paper, this unit has a good specification, but studio engineers tend to select their favourite compressors by ear as mere figures cannot tell the whole story. If they did, valve compressors would never get a look in, but as matters stand, they seem to be making something of a comeback.

Compressors should be smooth and unobtrusive in operation unless they have been deliberately set up to give a special effect and the GC2020 passed this test with flying colours. Increasing the attack time allows the natural attack of a sound to sneak through unchecked and this gives a delightful punch to drums and basses. Naturally a compressor will even out the dynamic range of a signal by attenuating its peaks and lifting the low passages, but unfortunately it also lifts any noise present in these quiet sections.

This is where the expander gate comes into its own, because it can be set to behave like a conventional noise gate. It will mute low level signals such as tape noise or sound spillage in the gaps between drum beats and so produce a cleaner sound. Providing that the original signal isn't too noisy, the gate can be very unobtrusive in operation, though its use on complete mixes is usually limited to cleaning up the beginning or end of a track.

Processing a complete mix through the compressor managed to thicken the overall sound without altering its character noticeably - another good test of a compressor.

Conclusions

As far as the serious home studio is concerned, this compressor/limiter could be considered as being virtually perfect. As far as the top flight professional studio goes, I couldn't say because I don't have the same quality of monitoring system that they would, but my guess is that it would satisfy most of them.

The inclusion of an expander gate makes this a very useful addition to anybody's equipment armoury, especially if you are short of noise gates, and it is yet another indication that Yamaha have their finger firmly on the pulse of serious home recording as well as on that of the professional market.

Further details from Yamaha-Kemble Ltd, (Contact Details).