Digitech Studio Quad 4

Multi-effects Unit

Published in SOS February 1999
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Reviews : Effects

Digitech's Quad 4, like its predecessor, can treat up to four signals independently, parcelling out its processing power according to your requirements. Could this be the only multi-effects unit you need? Hugh Robjohns finds out...

Digitech's Studio Quad, launched in 1996, was the first in a line of multi-effects processors which was continued in late '97 with the Quad V2. The start of 1999 sees the release of the Quad 4, which, like its forebears, provides four independent inputs and outputs and up to four effects-processing modules in 16 different configurations. With its 4-channel capability, the machine can used to process four simultaneous and independent mono effects, or the processors can be combined to operate in series or parallel to create more complex mono or stereo effects.

The Quad 4 offers 100 factory presets, plus a further 100 user memories, and provides a comprehensive range of effects, including the usual reverb, delay, chorus, phasing and flanging, auto-panning, tremolo, vocoding, EQ, rotary speaker simulation and dynamics processing. Every program is fully editable with an appropriate selection of parameters, although I found most of the presets quite usable in their initial state.

Judging By Appearances

The Studio Quad 4 is housed in an electric-blue, 1U rackmount box with an external power supply unit and simple, attractively arranged controls. Internally, the Quad 4 employs 20-bit delta-sigma converters: 128x oversampling devices on the inputs and the 64x oversampling variety on the outputs. A 24-bit signal path exists through the DSPs, with 48-bit internal calculations, and it all operates at a 44.1kHz sample rate. However, there's no digital interfacing capability on the Quad 4. The DSP chip is Digitech's own standard S-DISC II system.

DIGITECH QUAD 4 £400
pros
Flexible configurations.
Comprehensive range of effects.
Generally good sound quality.
cons
External power supply.
Weak pitch-shifting algorithms.
summary
A useful and versatile processor, offering very competent sound quality in the majority of cases. Some of the reverb algorithms can create very rich and dense sound spaces, and there's plenty of MIDI capability, plus a simple, uncluttered user interface.

The rear panel of the Quad 4 is fairly spartan. First up are four quarter-inch sockets for the inputs and four for the outputs. These are standard jack connectors configurable through the software menus for -10dBV or +4dBu operating levels, and the outputs are electronically balanced. A pair of DIN sockets provides MIDI In and Out/Thru, and there's another quarter-inch socket for a footswitch. Standard single-switch pedals operate only the bypass facility, but Digitech's own three-button footswitch enables program increment and decrement as well. Finally, there's a 4-pin DIN socket for the external power supply.

Fortunately, the front panel of the device is every bit as clear and simple as the rear. The power switch is a large rectangular push button with a protective fence around it, adjacent to a large, backlit yellow LCD panel. The operational controls are gathered into five distinct groups of buttons, and a large rotary encoder completes the lineup.

The LCD carries a wealth of information, but manages to present it in a reasonably clear format. The current program is always shown by a large numeric readout in the top-left corner, along with a textual description in a 24-character information line. This information line is also used to show parameter names during editing, and utility or auxiliary information when other menus are in operation. Immediately under the numeric display are three status indicators to show whether the current program is a factory, edited factory, or user setting. Below that, a row of digits indicate the current position within the menu structure during editing and utility functions.

On the right-hand side of the LCD are four alphanumerical parameter data displays (any additional parameters being available on further menu pages as necessary), four small, uncalibrated input level bargraph meters, and the effects routing matrix pictogram. This last section provides a very clear graphical illustration of the way the various effects algorithms are configured, and which one is currently being edited.

The operational controls are all pretty self-explanatory -- and every button is illuminated, so the current status of the machine is always obvious, even from a distance. The first grouping of controls contains two horizontal rectangular buttons labelled Program and FX Edit. The Program button is activated automatically when the machine is powered up and returns the system to the normal operational state from any other mode. It's also used to enable direct comparisons between a standard factory preset and a user-modified one. The FX Edit button allows parameter adjustments to be made to the selected program, even if it is a factory preset, although a modified version can only be stored as a new user preset.

The next control group contains four vertical buttons numbered 1 to 4, which are used to select an algorithm module and its parameters for adjustment. They are also used to select channels when setting the input levels. The third group contains another four buttons which allow selection of the Next and Previous menu pages, plus Store and Utility. This last provides user adjustment of settings such as screen contrast, MIDI channel, program change mapping, SysEx dumps, and a full factory defaults reset.

The last section has another pair of buttons, the first of which alters Input Levels in conjunction with the data wheel and parameter select buttons. The second button is labelled Bypass, but actually just mutes the effects part of the signal, leaving any dry component unaffected (and at whatever level it has been set to). A large rotary encoder with a tactile indented action completes the operational facilities.

In Use

The Quad 4 is fairly intuitive to use, although some functions can take a while to figure out by poking and pressing buttons alone! However, the manual is comprehensive and provides helpful hints and notes throughout, even if it is a little uninviting in terms of its layout.

Each of the preset programs has a number of alternative algorithms arranged in two banks -- Bank A always contains a dry signal in the patch in addition to the wet to allow in-line applications (for example, processing a guitar for live onstage work), while Bank B patches only carry the processed signal for applications within an effects loop (with a mixing desk having conventional aux sends and effects returns, say).

Repeated pressing of the FX Edit button cycles around the available processor algorithms in a given effects configuration (see the 'Processing' box on page 184), and when the required algorithm has been selected, its parameters are accessed through the various menus, via the Next and Previous buttons.

As soon as any detail has been changed, the Store button illuminates to remind you to save the new settings. As mentioned earlier, it's possible to compare an original factory preset with its user-modified version by pressing both Program and FX Edit buttons together. This reloads the factory preset momentarily, and pressing the FX Edit button again returns to the modified version. The trap is that if the Program button is pressed instead, the machine remains with the original factory preset and the user-modified version is lost.

  Processing  
  I counted 57 different effects algorithms in the Quad 4. Many are available with alternative levels of complexity, requiring varying proportions of the machine's DSP capability. The DSP resource is divided into quarter segments and the effects algorithms require either one, two, three or all four quarters of that resource, depending on their complexity and quality. For example, the 11 most complex algorithms require the entire DSP to run, and so can only be used in isolation -- programs such as the stereo 15-band graphic EQ, stereo detune, smooth pitch-shifter, stereo GigaVerb and the complex room echo. At the other end of the scale, 23 of the algorithms can be run in just a quarter of the DSP and so can be combined to produce more complex effects chains. Multiple algorithms can be combined in all manner of ways, as long as the total DSP requirement does not exceed four quarters.

Speaking of configurations, the Quad 4 boasts a total of 16 options -- four more than the previous Studio Quad V2. These include all the obvious parallel, serial, and split combinations, with three arrangements involving combinations of quarter and three-quarter modules, two configurations for pairs of half-modules, five configurations for a half module and two quarters, and a further five for a group of four quarter-modules. The selected configuration is displayed graphically on the LCD screen.

 
I found editing programs fairly tedious, as a great deal of button-pushing is required to find the right page (there can be up to eight) and select the right parameters. Once the desired parameter has been found, it's adjusted with the rotary encoder, but this does not appear to be velocity sensitive, so it can take a lot of revolutions to achieve a specific value. However, the wheel has one very nice feature: when winding a particular value down, it will stick when it reaches zero until the control stops rotating. Further turns can then access negative values (if appropriate). I found this very useful in the equaliser modes and when using other programs with parameters which had both positive and negative values.

The complexity and number of parameters available to each algorithm depends on its proportion of the total DSP resource (see the 'Processing' box opposite). Obviously, the programs which require the whole DSP have the most elaborate range of parameters, whereas quarter-DSP algorithms have a fairly rudimentary selection. For example, there are a total of 35 parameters associated with the variety of reverb programs, although the most any one program uses is around 20 and the least is three! Some of the parameters are rather obscure, or have obscure abbreviations, but the manual contains 13 pages of descriptions and explanations covering all available parameters in every effect algorithm.

The Quad 4 is also very well equipped for automatic parameter adjustments, which can be made either over MIDI, via the 128 continuous controller commands, from internal LFOs (with a good variety of wave shapes), or from the program signal's own dynamic envelope -- this last being particularly useful in creating some very expressive effects patches. Programs have up to eight controller assignments available and the links between parameters and controllers are all easily set up.

Setting input levels manually is fairly arbitrary because the metering is uncalibrated, but is easy enough to do, by pressing the Input Levels button to activate the mode, then one of the four parameter buttons to determine which input to adjust with the rotary encoder. However, there's also an automatic levelling mode, accessed by depressing and holding the Input Levels button for a couple of seconds. For eight seconds the machine then examines the signal at any inputs selected with the four parameter buttons, and adjusts the input gains accordingly. I found this mode extremely efficient and accurate, given a reliable input signal.

Utility functions, such as adjusting LCD contrast, selecting the MIDI channel, and mapping of the 128 MIDI program change commands to a selection of the 200 programmed effects in the Quad 4, are all very straightforward. There are also facilities to make SysEx dumps or uploads of program data to an external data filer, computer or another Quad 4.

Other utility functions include defining the reference frequency for the harmony pitch-changer algorithms, and setting the output signal level reference (-10dBV or +4dBu).

Listening

The reverbs vary in quality from very good to entirely average, depending on the algorithm chosen and the allocated proportion of DSP power. In particular, the GigaVerbs are very nice and smooth, with a good range of adjustability, and the reverse and gated options are very usable. The simple time-domain effects are all excellent, especially the various flangers and phasers, which are rich but quiet. The chorus algorithms are also very pleasing, as are the pseudo-analogue delays.

Quad 4 pitch-shifters exhibit the all-too-common mechanical twang, even with modest shifts, but the detune algorithms are better. As a big Hammond fan, I was automatically drawn to the rotary speaker algorithm and was pleasantly surprised at how realistic the effect is -- especially after some minor tweaking to the bass and horn rotor speeds and ramp times. The dynamics section comprises a compressor and noise gate, but these are difficult to set up, as there is no provision for a gain-reduction meter, so the user can't tell how hard the machine is really working.

The vocoder algorithm works well enough (though it's rather limited in its capabilities), but the envelope filter is far more effective, in my opinion. The eight equalisation programs all work adequately, especially in the context of severe EQ for effect. However, I couldn't imagine choosing to use the Quad 4 for more everyday EQ purposes.

Conclusion

On the whole, the Quad 4 is a very worthwhile piece of kit which has a wealth of capabilities. You have the option to process four channels independently, to create complex combination effects for mono or stereo signals, or to blow everything on a single, higher-quality mono or stereo effect. It would perhaps have been nice to see some dedicated surround programs, as provided by Sony's new V55M (see SOS January 1999), but realistically few units of this price level offer these. The vast majority of effects are competent and highly usable, and even the simplest are quiet and clean. This, combined with the sheer versatility of the machine, ensures that the Quad 4 will stay in the rack when other units have been consigned to the skip.

 information
information *£ £399.95 including VAT.
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