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Getting Teknikal


With the price of digital reverb steadily falling, what do top of the market models offer that budget ones do not? This model from Klark Teknik is at the forefront of reverb technology and incorporates some very sophisticated design work.


Less than a decade ago, the plate was the generally accepted method of generating studio quality reverb, but even the best plates can only produce a limited range of effects; you can either damp them, EQ them or both and that's about it. This, combined with their inherent disadvantages in terms of tricky acoustic isolation and background noise has let the digital unit take over as the most popular means of creating both natural and special effect reverb simulations. However, natural reverb is a very difficult thing to synthesise.

Back To Nature



The main problem in designing a reverb unit is soon evident when we examine reverberant effects in nature. When a sound is initiated in an enclosed environment, it is reflected and re-reflected from all the surfaces that it encounters until the density of reflections quickly becomes so high that individual echoes cannot be distinguished. This effect is known as diffusion, and it transpires that a very dense reverb pattern must be generated before the human ear will accept an electronic simulation as being the real thing. When you consider how the electronics of a digital reverb system goes about its business, you begin to appreciate the problem.

Digitisation



When a signal is fed into a digital reverberator, it's sampled in much the same way as it is in a simple digital delay unit, but there the similarity ends. All a delay has to do is to clock the signal in and out of a block of memory without performing any further processing before reconverting the signal back to analogue, but at this point the reverb machine's job has only just started.

The DN780 uses 16-bit linear coding which puts its noise and distortion capabilities on a par with CD recordings, but this makes life very difficult for the designer. Looking inside this digital reverb, you might think that you're examining a computer and this would in fact be very much the case (in fact - two computers) as all the clever work is done in software. During the period of one sample, the computer has to perform hundreds of operations to 32-bit precision to generate the many thousands of delay taps required to synthesise realistic reverberation, before moving on to the next sample. If the unit's bandwidth is 12kHz the time taken to process one sample will not be longer than 35mS. Obviously this is no mean feat and the DN780 uses a separate digital signal processor (DSP) which combines parallel processing with pipelined architecture, and a state of the art arithmetic processor IC about the size of a Yorkie bar to perform this task. What it all adds up to is the ability to create a very dense reverb to digital recording standards and for this, Klark Teknik have coined the phrase Added Density which is now their trademark.


Practical Considerations



Most of the boringly practical bits are situated on the rear panel such as the input and output XLR sockets and the remote control socket. The unit is fan cooled by one of the quietest fans that I have ever encountered and there are a couple of output level presets in case you want to match the levels to a nonstandard system. Mains is supplied via a standard IEC connector which in this case contains an integral mains fuse.

Looking inside the case reveals a busy but very tidily engineered design with none of those tedious edge connectors to go intermittent just when you don't need it; this unit is definitely built to survive the road as well as the studio. The main reverb processing is performed by a 16-bit digital sound processor and a less sophisticated 8-bit processor is used to look after the house-keeping jobs such as driving the front panel display and monitoring the front panel buttons.

Features



The DN780 looks deceptively simple in its 2U rack case and indeed, is very simple to operate. As with all such units, you really need to read the handbook through a couple of times but most of the controls do just what you would like them to do and only the operation of the special effects settings require any special attention.

Like most truly professional pieces of equipment, this model features updateable software so that it should never become obsolete and even MIDI add-on boards are to offered as options in the near future. Both the input and the stereo outputs are balanced, the input electronically and the outputs via transformers, and the bandwidth of the delayed sound is virtually flat from 20Hz to 12kHz. The distortion is quoted as being less than 0.03 per cent at 1 kHz and the dynamic range is typically 85dB which means that this is one of the few units currently available which can be used with confidence on work intended for digital mastering.



"Like most truly professional pieces of equipment, this model features updateable software so that it should never become obsolete and even MIDI add-on boards are offered as options in the near future."


Before getting down to details, it's worth looking at the general facilities provided by this unit.

Basically...



What we have here is a unit mainly dedicated to creating reverb effects, though in terms of hardware there is no reason why more delay effects should not be available and I believe that the next software update is likely to include some interesting delay effects including stereo chorus. There are one or two such effects resident in the current software including Straight Delay, Sound On Sound, ADT and Multi-Tapped Delay, but the majority of the effects available are as you might expect reverb simulations. These include gated and reverse reverb effects which are currently very popular.

There are 28 preset effects set up ready to go which can be readily modified and stored as a user memory if required, and you can store up to 50 user sounds in the memory for instant recall. The maximum reverb decay time is a massive 99 seconds (if you don't count the Infinite Room setting) and the preset effects include a selection of Halls, Plates, Rooms and Chambers with five variations of each.

Included in the price is a remote control unit which gives slider control of the major parameters such as Pre-delay, Reflections Level, HF Decay and Reverb Decay Time (though the sliders may be re-allocated to other parameters if required). It's also possible to step through a pre-arranged sequence of effects using this unit.

Parameters



There are seven user variable parameters for each reverb setting, though these are somewhat different when we come to the special effect section; but more of that later.

First is Pre-Delay which is variable from 0 to 990mS in 1mS steps and this dictates the time delay between the original sound and the onset of reverberation. The real life counterpart to this parameter would be the time delay for the sound to reach the nearest wall and return to the listener. As sound travels at roughly one foot per millisecond, you can work out the psychological effect of this control by allowing two millisecond a foot for the round trip.

Decay Time is self evident and may be varied from 0.1S to 99S which is more than adequate for any reasonable effect. At the maximum setting, three drum beats could last for the whole duration of a single!

Room Size changes the spacing and diffusion rate of the reflections to simulate an environment of a given size and the character of the sound changes notably as you progress from a hypothetical concrete garage to a cathedral. The size is displayed for a cube having linear dimensions variable between five and one hundred metres.



"The bandwidth of 12kHz may not look all that impressive to someone who is a hi-fi buff, but when it comes to producing a subjectively clean reverb, it's plenty bright enough."


Both the low and high frequency decay times may be varied by incrementing or decrementing their value to ±7 steps either side of the mid band decay time (ref 1 kHz). This again corresponds to a natural effect, in this case, how the wall materials reflect different frequencies with different efficiencies. A concrete or stone wall is going to reflect high frequencies very efficiently whereas a papered wall or a room full of soft furniture will have a quite different response.

Early Reflections; this is a very important part of the effect and is largely responsible for creating the character or acoustic signature of an environment. The shape, size and contents of a room will affect this parameter and the DN780 gives you a choice of five patterns, each containing up to 200 individual reflections. This is around ten times more than you get from even a better class of budget unit and is largely responsible for the natural sound quality. These reflections may be balanced in level against the rest of the reverb sound in ten steps, and the reflection spacing is affected by the room size control. So far so good but how do we control all these features?

The answer is... surprisingly easily, so let's have a look at the front panel controls.

Controls



At the extreme left hand side of the unit is the input section which includes a ten section LED meter so that you can keep an eye on the input level and it also tells you if the arithmetic processor is being overloaded; you do need to drive the unit sensibly if you are to take full advantage of its impressive signal to noise ratio. A rotary gain control is fitted to match the input level and there are two momentary action mute switches, one kills the reverb input and one the output. The Input Mute is very helpful for checking decay times.

Next comes the LED numeric display which shows parameter values and memory numbers, and below this are the parameter select buttons, Pre-Delay, Pattern/Level, Decay, LF/HF Damping, and Room Size. Also below the display are the parameter Up/Down buttons which are used to modify the parameter values; if an Up/Down button is selected and then its opposite number pressed without the first being released, the value steps through rapidly making for quick setting up.

To the right of the panel is the numeric keypad which can be used to call up the required memory location. This is a very simple procedure and involves only pressing two digits, there is no complicated ritual involving enter type keys. The STOre and SEQuence are also to be found on this pad and these are used to store user memories and to organise memories into the correct sequence so that they can be stepped through when this facility is required. A STOre status LED in the display window flashes when the STOre key is first pressed and extinguishes when it is pressed again at the end of a STOre operation. The SEQuence key is used together with the STOre key to set up a sequence of memories which may be stepped through later using the SEQuencer key. You may also notice three windows with the letters A, B and C tucked away at the bottom of the main display and this thoughtful inclusion tells you at a glance which version of software is fitted.

Lastly comes the Mains switch, the function of which should be no mystery.

Editing parameters is simplicity itself as all you do in effect is to select a parameter button and then increment or decrement the value until the desired level is found. This is repeated for all the parameters until you achieve the desired result and then the effect may be committed to memory if you want to keep it. If you try to store it into the location of a factory preset or an already occupied location, the display will politely say NO. To evict a memory involves a multiple button sequence to prevent accidental erasure of wanted effects.



"This is not a cheap unit by any means but it is less expensive than its quality might lead you to believe."


So, the operation and the layout looks perfectly logical, the specification looks beyond reproach and the presentation is both smart and functional, but all this technology is for the benefit of our ears, not our eyes, so how does it sound?


Studio Test



As usual, the first line of attack was via the drum machine to check out the subjective response to transients and the first thing that comes to notice, apart from the superbly smooth diffusion, is the detail contained in those initial reflections. It really has paid off including those two hundred odd reflections. By lifting the level of these reflections, the reverb can start to sound granular on drums but this effect is exactly what is needed to breath life into soft sounds such as vocals, flutes or subtle synth sounds. Changing the room size really does give the impression of doing just that and gives a convincing feeling of space around the sound being treated which is useful both in music production and film soundtrack work. The latter application really benefits from this ability to tailor the sound because the eyes and ears usually manage to rumble what's going on when they are being told different stories.

The bandwidth of 12kHz may not look all that impressive to someone who is a hi-fi buff, but when it comes to producing a subjectively clean reverb, it's plenty bright enough.

The Plate settings are particularly good for producing tight drum sounds as might be expected, but the other environments can be used to good effect on percussion also. Vocals positively sparkle, particularly when a fairly high level of initial reflection is called up, and the beauty of the system is that you can set up a good sound very quickly with no messing about.

Special Effects



In the special effects department, the DN780 has a few tricks up its sleeve and the gated reverb effect, familiar to everyone by now, works very well. In this mode the Gate Time may be altered over a wide range using the Decay control whilst the Pattern Level control affects the density of the reflections. Pattern calls up the decay envelope for the effect which may be linear, gated or reverse, the other controls working as normal.

The straight delay effects are just that and are monophonic in that both outputs contain the same signal. The Pre-Delay control sets the delay time to a maximum of two seconds and, for continuous rapid adjustment, the remote control slider may be used instead.

ADT is a useful effect and the Pattern control in this mode dictates how many repeats are generated which may range from two to eight. The delay taps are routed to opposite sides to give a deep stereo effect and the Pre-Delay control sets the delay between the first and second 'voice'.



"As it stands, with the existing software, this is a superb unit that compares more than favourably with any digital reverberator regardless of price but that's not all."


Multi-Tap Echo is similar to the ADT effect except feedback may be employed via the Decay control to create a type of very coarse reverb which can be used creatively on most sound sources. This treatment is very textural and sounds much better than it looks on paper.

Sound On Sound is far removed from the primitive overdub facility found on cheap domestic tape recorders and is in effect a way of creating a sound loop and then adding to it. With a maximum loop length of two seconds, the decay control acts as a loop erasure function where the amount of erasure may be varied from 0 to 100 per cent. Using the Level and Up keys, the input to the loop may be opened and closed at will so that you can easily control when new sounds are to be allowed into the loop. Like the Delay, this is a mono effect.

Infinite Room is definitely a special effects program as the sounds being treated never die away but reverberate around forever. Like the Sound On Sound setting, you can control when sound is to allowed into the 'Infinite Room' so that layered sounds may be built up.

Summary



This is not a cheap unit by any means but it is less expensive than its quality might lead you to believe. All the contemporary reverb effects can be created very quickly, which is important when time is money, but equally important, natural sounding reverbs or bizarre special effects are also close at hand. All the conventional reverb effects have a wide stereo image with a lot of depth and are also totally mono-compatible.

Apart from the high and low frequency decay controls, there is no on-board equalisation that is accessible to the user but I believe that there are digital parametrics in the software that are used to tailor the character of the reverberant sound. They change with pattern, room size and RT time controls.

The remote control unit, which is included in the price of the unit, does not give you simultaneous access to all the functions available but it does let you get at the important ones during a mix, particularly the reverb decay time. The sequencing function is also a simple but sensible consideration and this too is prevented from accidental erasure by virtue of the multi-button sequence that is needed to erase it.

Ease of use cannot be stressed too highly when we are constantly being bombarded by hi-tech gear that takes a week to learn how to operate and in this area, the Klark Teknik DN780 takes some beating.

As it stands, with the existing software, this is a superb unit that compares more than favourably with any digital reverberator regardless of price but that's not all. Because of the sophistication of the hardware at the heart of this system, future software developments won't be limited due to lack of performance in this area, so as far as reverb goes, this unit can in theory do anything that the programmers ask it to do. Voorsprung Klark Teknik as they say in Kidderminster.

MRP for the DN780 is £3950 + VA Tand further information is available from: Klark Teknik Plc, (Contact Details).



Previous Article in this issue

Making Tracks with the Vesta Fire MR1

Next article in this issue

Pedal Power


Home & Studio Recording - Copyright: Music Maker Publications (UK), Future Publishing.

 

Home & Studio Recording - Nov 1985

Donated & scanned by: Mike Gorman

Gear in this article:

Studio FX > Klark Teknik > DN780


Gear Tags:

Digital FX
Reverb

Review by Paul White

Previous article in this issue:

> Making Tracks with the Vesta...

Next article in this issue:

> Pedal Power


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