Fostex 3070 Compressor/Limiter
Dave Ward of Gateway Studio expresses his views on this budget-priced Compressor/Limiter from Fostex.
A Compressor/Limiter is a device for reducing or altering the dynamic range of signals put into it. In our case this is likely to be music programmes. The dynamic range of our material is the difference between the quietest sound experienced and the loudest crescendo. The Compressor tends to make the quieter sounds louder and to hold back the peaks of the stronger signals.
The Fostex Model 3070 is a cost-effective Compressor/Limiter which has the parameter adjustment facilities of many devices several times its price. It can operate in the stereo mode or as two mono units.
A Compressor only operates on signals that are above its threshold level which is usually set by the sensitivity control which, in the case of the Fostex Compressor, is the input control to the device.
Compressors work on a ratio of input signal to output signal. For instance, working at a ratio of 4:1, for every 4dBs of input level gain experienced by the Compressor above the threshold setting, the Compressor will give 1dB of gain at its output. The ratio control on the Fostex 3070 changes the compression ratio continuously from a 1:1 setting (no compression) through to 20:1 (hard limiting) and then on to infinity.
The Compressor/Limiter controls must also have the ability to adjust for music programmes of differing attack and decay times (the envelope of the sound). On the model 3070 the attack times are continuously variable from 0.2 to 20 msecs. The attack time is the time that it takes the Compressor to react to the signal exceeding the threshold. The release time which is the time it takes the Compressor to recover to its unity or 1:1 position, is continuously variable from 50 msec to 2 seconds. We shall discuss attack and release settings later in this article.
The input control of the 3070, which is a rotary control, performs two functions simultaneously. By increasing the input level, one is effectively increasing the input experienced by the Compressor above the threshold level. The output control is designed into the circuitry before the by-pass in/out switch which, on this device, is labelled COMP for compression in/compression out. While this, to some people, may seem to be a small point, this configuration is, in fact, very convenient, as it enables the user to make a true comparison between input and output signals without having to re-adjust the output controls.
The dimensions of the device are 17" wide x 1¾" high x 8¼" deep and I understand attachments are available to prepare it for 19" rack mounting. This Compressor also incorporates an expander gate which is useful for eliminating unwanted noise that can sometimes occur by over-use of compression which may be necessary on certain types of programme material. On each channel of the Compressor there is a meter in the form of a strip of light emitting diodes (LEDs) which indicate the amount of gain reduction being applied to our programme material.
On the rear of the unit are the input and output connections to the device which are on either ¼" jack or phono connectors. The inputs have been, in my view, cleverly arranged with 10dB pads behind the jack sockets so that, in conjunction with the input gain control, the Compressor's threshold can be matched to different pieces of equipment with varying operating levels. I found that the manual gave a very good indication of the operation of the input control but, unless one is aware of these different operating levels in terms of decibels of voltage (dBV) then the interconnections could become a little confusing.
On the rear of the unit there are also insert points for the patching of effects devices into the side-chain of the Compressor. These are arranged as phono jack sockets with a plastic-coated bridging pin.
We have used the 3070 on widely varying types of programme material, both in the school room, in the 4-track demo situation and in our main studio. In all these circumstances, we found that the device operated most satisfactorily and that the amount of distortion at extreme settings was surprisingly low.
Here are some of the occasions on which we used the 3070. We had recorded a nice, punchy backing track with drums, guitars and synthesisers but, when it came to recording the vocals we found that the vocalist, who did not have the world's best microphone technique, was getting lost in volume on the quieter passages and bursting out of the speakers and bending our VU meter needles on the louder passages.
By patching the Compressor into the vocal track we were able to tighten up the dynamic range so that the quieter passages could be heard and the louder passages were not then over-powering the backing track. This gave us a subjective increase in overall volume in the vocal track. This enabled us to use a little reverb and delay on the vocal and sit it nicely in the mix where we wanted it, with every word audible.
On the same session we wanted a really punchy bass sound, but on this occasion, both bass player and instrument must have been having a particularly 'flabby' day. We were able to clean up the sound of the bass with a little equalisation but it still lacked punch to drive the track along. Some gentle compression at a ratio of 4:1 and careful adjustment of the attack and release controls gave us the sound we wanted. How much easier it would have been, of course, if the sound was correct at source - then we could, perhaps, have used our Compressor creatively, rather than correctively.
The attack and release controls on a Compressor will have a very pronounced audible effect on the signal and, in general, should be set with reference to the sound on the monitor speakers. It is also good to bear in mind the obvious facts that, for instance, a snare drum has a much shorter attack and release time than, for example, a bowed violin.
I found the attack and release controls on the 3070 very easy to operate - in fact I found the device as a whole quite simple to operate and a delight to use, once I had spent some time reading the manual and the application notes.
The noise gate/expander function was particularly useful on one track where we had to compress a signal coming from a guitar amplifier. The amplifier had been 'miked' and the sound was fine when the guitar was playing and was covering up its own hiss but, when the guitar stopped, of course, because the Compressor was lifting up the quieter sounds (the hiss), this noise became excessive. The expander gate was able to close down the circuit so that we were able to record the sound of the guitar and not all the rubbish coming up behind it.
Great fun can be had by patching various effects and signals into the side-chain of the Compressor. Patching an equaliser into the side-chain of a Compressor and giving the signal a treble boost can, of course, help with sibilance and we found that the 3070 worked very well in this situation.
We also patched the 3070 across a stereo mix and used it in its stereo mode, linking the two sides of the Compressor with the stereo switch, which is on the front panel. In this position, the control settings relative to only one side of the Compressor will be those instructing the device. This prevents bad tracking or movement of the stereo image. In this way, by applying a little compression to the stereo mix and careful adjustment of the attack and release times, we were able to make a rather bland mix a little more exciting.
As with all Fostex products that I have come across, the 3070 is a very well made unit, which I found easy to use and would thoroughly recommend, particularly at its retail price of £262.32 including VAT.
The correct use of the Compressor is an art that takes some time and experimentation to achieve. I often think that manufacturers of equipment should go a lot further in giving much simpler explanations, even though this might entail writing more detailed manuals. In the case of the 3070, Fostex have gone a long way towards accomplishing this and are to be congratulated, but looking through the eyes of the layman, I can still see several areas of confusion.
Further details from all Fostex stockists or Bandive, (Contact Details).
Review by Dave Ward
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