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The Intelligent One

Studiomaster IDP1 Dynamics Processor

What is an 'Intelligent Dynamics Processor' and why have it MIDI controllable? David Mellor answers these and other probing questions as he explores the IDP1 from mixer manufacturer, Studiomaster.

It could be the bout of the century: Sound On Sound's intelligent reviewer pits his wits against Studiomaster's Intelligent Dynamics Processor. Is it a contest of equals or does the Studiomaster's microprocessor give it an unfair advantage? David Mellor is at the ringside.

The so-called 'intelligent' dynamics processor is something of a novelty at the moment. We have compressors and we have noise gates, some products being more sophisticated than others, and some which combine several of the facilities of both in one unit. Control, up until recently, has been strictly analogue. One knob - one function, not a digit in sight. Old fashioned knobs have the advantage that you can easily see what they are set to, but the disadvantages of taking up a lot of panel space and their inherent non-programmability.

Whether or not you are an admirer of control knobs, it is the age of the digit and we have to accept digital control for the benefits it offers. It is now the turn of the compressor and noise gate to be digitised - and as we shall see, MIDI-fied too.

Assuming for the moment that the Studiomaster IDP1 is as intelligent as it claims, just where does it fit into the market place? My home studio, for instance, is compressed and gated courtesy of the industry-standard Drawmer DL221 and DS201 units. It is with these that the IDP1 has to compete, not just for the pound in my pocket but for the custom of just about every studio going. It's not good enough just to bring out a flash new gadget. It is a business axiom that to compete you have to make a better product or make it more cheaply. Studiomaster have side-stepped slightly and made something that is different. Pricewise, it's about the same as the Drawmer 221/201 combination. Whether or not it is an improvement is the key question - which I shall do my best to answer in due course.


'Well, what does it sound like?', they all cry. You would have to be Poet Laureate to be able to answer that one in print! It is an important matter though, because all compressors have a distinctive 'sound' which makes them good at some jobs, not so good at others. Let me re-phrase that - some engineers find them good at some jobs and other engineers find them good at other jobs. You see, it's a question of personal taste. I'll go so far as to say that the IDP1 sounds at least as good as my Drawmer and that it didn't make any of the undesirable noises - usually clicks and thumps - that poorly designed compressors produce. It's a professional unit and you shouldn't have any trouble on that score, but you'll need to listen yourself to judge the 'sound' of the IDP1. I should also mention that although it is digitally controlled, audio processing is handled by pukka analogue devices, like the old manual units.

Having got that out of the way, I can move on to more concrete matters - the facilities. What does the IDP1 do that other compressors and gates don't? Is all that digital control a good thing?

The IDP1 is a versatile little gadget, all packed into a 1U rack-mounting box. As well as being a compressor, it can be a limiter. As well as being a noise gate, it can be an expander - or a ducker. To add to all that, when the IDP1 is fulfilling its role as a compressor, there is an additional expander gate function available to reduce any noise that the compressor action may emphasise.

It's probably best to look at the photo at this point, starting with the display and moving on to the controls.

Trying hard to be user-friendly, the IDP1 powers up with a cheery scrolling 'HELLO' message, followed by the software version number. The four bright 7-segment LEDs are used to give the user all the numerical information he or she needs. Underneath and alongside are four red LEDs which indicate what type of information is being displayed - seconds, milliseconds, microseconds or dB. The topmost LED bargraph is a horizontal VU meter, showing what level the unit is putting out. The lower bargraph is a display of the amount of gain reduction. Over on the right are nine pushbuttons which are the principle controllers of the machine:

- PROGRAM, in conjunction with the increment/decrement keys, is used to select any of the 128 programs which the IDP1 can store. 28 factory set programs are provided which can be used as convenient starting points for just about any setting you could possibly think of. (See separate panel.)

- SELECT is used to select either Channel 1 or Channel 2 for editing. The bargraphs show VU and gain reduction for the chosen channel.

- MODE changes the selected channel from compressor to gate mode and vice-versa.

- LINK, as it suggests, links the two channels together for stereo operation.

- STORE, is used to put any user program into memory. There are 100 user memory locations available, which ought to be enough!

- RECALL is the converse of STORE.

- INCREMENT/ACCEPT, DECREMENT/ CANCEL, are used for increasing or decreasing the value of a parameter being edited, and are also the confirmation keys for STORE and RECALL.

- MIDI allows the user to select the MIDI channel, for each channel of the IDP1, on which either note-on/off or pitch bend information will be received. More on this later...


Let's start by selecting Compressor mode on Channel 1. On an analogue unit, a compressor would have several control knobs: THRESHOLD, RATIO, ATTACK, HOLD and DECAY. The IDP1 has no knobs, instead the central bank of six buttons select the function you want to edit. The current value being shown on the numerical display. Let's set the threshold, which is the level above which the compressor action comes into effect.

First, make sure that you are adjusting the correct channel. The display should show 'CH.1'. Press THRESHOLD and the display will change to something like '-25' and the dB LED will light up to show that the threshold level is 25 decibels below 0dB. The up and down buttons can then be used to set the threshold level anywhere between —45dB and +15dB, which should be a more than adequate range. If this is all you need to change, then off you go and get on with the track. The display will always change back to 'CH.1' of its own accord after a little while, to show that the bargraphs are working from Channel 1's output.

The ranges of the different parameters are shown in a separate panel, and are adequate in every way. I haven't thought of a use for a 50 second release yet, but I'm sure someone will. I could expand on one or two points, the expander mode for one thing...

This isn't to be confused with the expander gate function, which is an extra facility on top of the normal compressor action. You will notice that the compression ratio can be varied from 1:2.5 to 50:1. 50:1 means that if the input level rises by 50 decibels, the output will go up just one decibel. This is known as a 'hard limiting' action, a 'soft' compressor action would be 2:1 - ie. for every 2dB the input goes up, the output increases by 1 dB. Putting the numbers the other way round creates expansion. A 1:2 ratio means that if the input increases by 1 dB, the output increases 2dB - causing an increase in dynamic range. As you can see, compression and expansion are just opposite ends of the same concept, so displaying them in this way makes a lot of sense.

The parameters of the gate are the same as those of the compressor, apart from RANGE, which replaces RATIO. Simple noise gates are just on/off devices. Either the signal gets through or it doesn't. If you use a gate, then you will know that more control than this is useful - or you are wishing that you had it! On the IDP1, the RANGE parameter sets the degree of attenuation applied when the gate is closed. Wait for my 'How It Works' article on gain control for more explanation of this, plus a few words on what ducks have to do with professional audio.

The one button I haven't mentioned yet is the EXP(ander) GATE. As you probably know, when you compress any signal you reduce the signal-to-noise ratio. For example, during the pauses in a vocal, background noise will come up in level. Since compression or gating is an either/or situation on the IDP1, an additional gate is necessary.

The control set on this function is somewhat less well supplied than on the full gating mode. There is just one parameter - threshold - which can be set from -45dB to +15dB. When the signal drops below the threshold level, the gate closes. Actually, it's quite clever because the range of the gate is automatically set according to the ratio you have set for the compressor. The higher the ratio, the greater the noise problem and the greater the range you need on the gate - and it's all done for you. Also, the attack time of the gate is proportional to the release parameter of the compressor. Handy.


Those ubiquitous five-pin DIN sockets get everywhere. I am, in fact, thinking of getting the software update to my toaster so that I can send program change commands to set it for different types of bread!

MIDI, on the Studiomaster IDP1, is used for more than just program changes. How about MIDI auto fade-in and fade-out? By putting the IDP1 into Gate mode and setting the threshold to 'off', it allows a MIDI note-on signal to initiate the attack phase and note-off to initiate the release phase of the cycle - any note (pitch) will do. If you set the attack time to the length of fade-in you want, and the release time to the length of fade-out, you can use a MIDI keyboard or sequencer to obtain perfect fades. If, like me, you can't afford Penny & Giles faders on your mixer, you will know the problem you get when you have faded both channels of a mix nearly to zero. The fader action gets very coarse at low levels and you usually get one channel disappearing before the other. It doesn't sound very professional and I have had to resign myself to re-doing the fade several times to get it dead right, then editing it in. With this feature of the IDP1, that could be a thing of the past.

There are a few other MIDI tricks which haven't such an obvious application, but with a little imagination...

For example, in Compressor mode, not only does a MIDI note-on initiate the attack phase, the MIDI velocity information can control the amount of gain reduction applied. Aftertouch can do the same thing. Alternatively, the pitch bend wheel of your MIDI keyboard can be set to do exactly the same thing. As I mentioned earlier, MIDI channel can be set separately for each IDP1 channel.


If I had three wishes, then at least as far as this machine goes, I would wish it came in a 2U box with two sets of controls and displays. OK, so it puts the price up, but if you are a professional user and you want a good compressor then you would be well prepared to pay the extra 30-40% it might cost. Give it balanced XLR inputs and this machine would be in Division One class. As it is, I found it a nuisance to have to keep changing the channel I was looking at, both when editing parameters and simply looking at what the bargraphs were doing.

My second wish would be for an output level control. Yes, I know they are going out of fashion, but they really are useful, especially on a compressor. When you are compressing a signal, then obviously 'squeezing' it down in level is going to result in a lower output. If you are compressing for effect, then you need to be able to compare the compressed with the uncompressed version of your signal - at comparable levels. The IDP1 has the necessary bypass switches for each channel but no 'make-up' gain control. The manual says that make-up gain is provided automatically, and indeed it is but not always in the right amount. Clever, but not quite clever enough - how can the automatic make-up gain circuit know by how much you want to exceed the threshold? I must not be too strong on this point because for most purposes the system will be OK as it stands. Give me the automatic system and an output level control and I'll be ecstatic!

While I'm in a critical mood, let me have a go at something which is becoming all too fashionable - the single jack insert point. As with any decent compressor or gate, the IDP1 provides separate access to the control circuitry so that you can do things like de-essing and envelope triggering. The insert point uses a single stereo jack for each channel, the 'tip' being the send and the 'ring' being the return. Lots of manufacturers do this and the criticism is spread equally among them. Things wouldn't be half as bad if they could all agree on the same convention, but even so, the sight of two great thick cables stuffed into one poor little jack plug brings tears to the eyes.

The most peculiar thing is that a compressor or a gate doesn't even need a send - what on earth would you use it for that you couldn't manage with a parallel on the jackfield or even a simple Y-splitter? Drawmer got it right on their DS201 noise gate - a sidechain input with a switch on the front for internal or external source. (Pity they didn't do the same with their DL221.) Returning to the good points of the IDP1, of which there are many, let's summarise some of the reasons why you might buy this unit instead of traditional compressors and gates:

- compact (1U)
- 128 programs
- compression or expansion
- gating or ducking function
- extra expander gate to reduce compression-induced noise
- MIDI control
- automatic make-up gain

I could go on to include the traditional features this unit includes:

- full range of parameter control (except output level)
- stereo linking
- bypass
- sidechain insert
- sidechain listen
- good audio performance

I could also mention something which you will only get on a digitally controlled analogue unit like this - automatic recalibration. Actually, it wasn't implemented on my version 1.3 model but you should find it on version 1.4 in the shops. Most manufacturers won't tell you this, but VCAs (Voltage Controlled Amplifiers) are prone to drift with temperature. Studiomaster are willing to own up to the fact that a 2dB error in control settings can be expected, so what use would the apparent accuracy of numerical displays be, set against this? However, on version 1.4, you will be able to send a MIDI program change 00 and all will be put right, automatically. As I said, I haven't seen this in action, but it definitely deserves a mention.


Despite my slight criticisms, most of which can be traced to a desire to have this machine in a bigger (2U) case, I am very favourably impressed by the Studiomaster IDP1.

If you are happy with the quality and quantity of the compressors and gates you already have, then there is probably no need to change to this. Bear in mind, however, that the IDP1 is the first of many digitally-controlled analogue dynamics processors to come and your equipment rack may start to look a little dinosaur-like without something like it. This is one field, undoubtedly, where you need to look at the competition to find something suitable for your needs. Dynamics controllers of this nature all do similar things, so it's pointless being overstocked with them. They do differ in detail, however, and it's these details that could make all the difference.


program number type name description
100 compressor bass guitar 1 general bass compressor
101 compressor bass guitar 2 punchy bass compressor
102 compressor drum comp 1 general drum compressor
103 compressor drum comp 2 punchy drum compressor
104 compressor guitar 1 general guitar compressor
105 compressor guitar 2 clean snappy guitar
106 compressor guitar 3 sustained guitar
107 gate softener guitar softener
108 compressor vocal vocal compressor
109 duck vox voice operated fader
110 expander expander 1 gentle expander
111 expander expander 2 hard expander
112 gate reverb 1 gated reverb 1
113 gate reverb 2 gated reverb 2
114 gate drum gate drum noise gate
115 gate noise general noise gate
116 compressor AM comp AM radio compressor
117 compressor EM comp FM radio compressor
118 compressor classical stereo classical music
119 compressor limiter stereo programme limiter
120 compressor soft comp stereo soft compressor
121 compressor punchy stereo punchy compressor
122 duck fade-in MIDI auto fade-in
123 duck fade-out MIDI auto fade-out
124 expander velocity MIDI velocity control
125 expander pitch bend MIDI pitch bend fader
126 gate MIDI gate MIDI triggered gating
127 duck MIDI duck MIDI triggered ducking

IDP1 Control Ranges

Threshold -45dB to +15dB
Ratio 1:2.5 (expand) to 50:1 (compress), plus limit
Attack 30 microsecs to 1 sec
Hold 200 microsecs to 1 sec, plus off
Release 30 millisecs to 50 secs

Threshold -45dB to +15dB
Range gate -99dB to 0dB, duck -99dB to 0dB
Attack 30 microsecs to 1 sec
Hold 200 microsecs to 1 sec, plus 'off'
Release 30 millisecs to 50 secs

Price £684.25 inc VAT.

Contact Studiomaster, (Contact Details)

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Wind Synthesizers

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How Analogue Synthesizers Work

Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.


Sound On Sound - Dec 1987

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Studio FX > Studiomaster > IDP 1

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Review by David Mellor

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