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Sound Control: Alesis Quadraverb

Four simultaneous effects and real-time MIDI control are features found on several recent effects processors, but the Alesis Quadraverb is the first to bring both together in a single unit. Paul Ireson lends an ear.



The Quadraverb provides up to four effects applied simultaneously to the input signal, and also has the facility to control effects parameters in real time via MIDI. At this moment, such a combination of features makes the Quadraverb unique - though progress being what it is, for how long that remains the case is anybody's guess.

Both features are individually another step in the development of effects processors, though neither are by any means unusual, having appeared on several existing units. For example, the ART Multiverb [reviewed SOS Jan 89] produces four effects simultaneously, and several other units offer MIDI control over effects parameters. The Digitech DSP128 offers three simultaneous effects and MIDI effects parameter control. So, the Quadraverb is evolutionary rather than revolutionary in its design - but look where evolution gets you. From primordial soup to creatures capable of producing TV documentaries about French cuisine... but I digress.

To get down to specifics, the Quadraverb is a 16-bit stereo effects processor. Four effects sections are provided: EQ, Pitch, Delay and Reverb. Several effects from one box is not new (SPX90, MIDIfex, etc) but offering several at once is far more interesting, and makes for a very versatile processor. The way in which these effects are combined is subject to certain limitations, but on the whole these are not too restricting. Up to eight different effects parameters can be modulated by external MIDI controllers (aftertouch, velocity, etc) - a very useful feature which allows the control of effects to approach the kind of control which players and composers now take for granted on synthesizers. Would anyone be interested in buying a new synth that responded only to Note On/Off and Program Change messages, and ignored Velocity, Pitch Bend, Aftertouch and Modulation? I thought not, so why should effects units not take their MIDI implementation a little further than just accepting Program Change messages. The cost in extra hardware is somewhere between 'minimal' and 'zilch'. All it takes is clever software and a fast processor.

APPEARANCE



Before we explore the inner workings of the Quadraverb let us, in time honoured review fashion, take a quick tour round the exterior.

To the left of the front panel is a four segment LED headroom indicator. Adjacent to this are two rotary pots for input and output levels, as expected, but there's no mix level control. Oddly enough, the Quadraverb omits this very useful control. Of course, the effect/dry balance can be changed by accessing and editing a couple of effect parameters, but I think that most users, myself included, would prefer a real knob.

A backlit 32-character LCD is provided to display all pages available for editing effects: next to it are the Page and Value buttons, which allow you to scroll through pages and parameter values. An interesting feature of these buttons is that they are pressure sensitive: the harder you press them the faster the values increment. At first I thought this was totally wonderful, but I revised my opinion after a few heavy editing sessions in which I scrolled from 2,000 to 18,000 Hz, in 1 Hz steps, several times. My index finger rapidly lost interest in proceedings, and made it quite clear that it would rather be relaxing on a TV remote control. So, a slightly wonderful feature perhaps.

Next on the front panel comes two rows of buttons for selecting effects sections and assorted parameters for editing - in conjunction with the Prog(ram) button they also allow effects programs to be called up by number, rather than just scrolled through with the Value buttons. There is also a Bypass switch, which strangely didn't seem to bypass on all effects programs when I tried it - sometimes it just killed all output. The reason for this is related to the Quadraverb's internal signal routing: the signal appearing at the stereo outputs is a combination of Direct and Effect signals. What the Bypass switch does is simply to mute the Effect output, so if the Direct signal level in an effects patch is set to zero. Bypass will simply kill all output.

This, and the absence of any front panel mix control, lead me to believe that the Quadraverb is best suited to being patched into the effects loop of a mixer, rather than in between an instrument and a mixer. However, in this case, all the preset effects would need to be edited to set the Direct levels to zero and Effect levels up to maximum. Just pushing a Mix slider all the way to one side would be so much easier, setting a global balance for all programs. As it stands, most of the Quadraverb programs actually have the dry/wet balance set so as to be suitable for patching straight after an instrument's outputs. Odd. Perhaps a revision to the Quadraverb's operating software could include a provision to set global levels for Effect and Direct outputs, overriding those levels set within individual programs. How about it Alesis?

Out back, the rear panel includes stereo inputs and outputs via two pairs of quarter-inch jacks, and two footswitch jacks: one for incrementing programs, and one for enabling the bypass function. There are two MIDI sockets. In and Out/Thru.

ARCHITECTURE



The Quadraverb stores its effects as programs: 100 memory locations are available, and 90 of these come factory-filled with presets. You're not stuck with them, however. You can edit the presets to your heart's content - though should you decide that you've spoiled somebody else's perfectly good idea, you can always recall the original factory preset, or indeed any of the other factory presets, to that memory location, as all 90 presets are duplicated in ROM.

At the heart of all Quadraverb programs are the four effects sections - EQ, Pitch, Delay and Reverb - and their Configuration, that is how the signal path is routed from one section to the next. There is a certain amount of trade-off between the number of effects used and the complexity - though not quality - of individual effects. The five Configurations available are: Quadmode, EQ-Pitch-Delay-Reverb; Leslie-Delay-Reverb; Graphic EQ-Delay; 5-band EQ-Pitch-Delay; 3-band EQ-Reverb.

Quadmode is the only mode in which all four effects sections can be used as such - the other modes presumably use the processing power of missing sections in different ways. Sometimes it is fairly clear how this happens, other times less so. For example, the Leslie Configuration uses the EQ and Pitch sections to create an ad hoc effects section called 'Leslie'. Looking at the other Configurations, it seems that the processing power required to create an 11-band Graphic Equaliser is the same as that required to create a 5-band Parametric EQ plus a Pitch effects section.

SO WHAT DOES IT SOUND LIKE?



Before delving deeper into Configurations and Programs, the first question to be asked of any effects unit is of course "what does it sound like?". In the case of the Quadraverb, the correct answer is "excellent". All four effects sections sound beautifully clear, adding very little noise to input signals. I found I had to crank the Harrison/Urei monitoring system in the SOS studio up to fairly dangerous levels before the noise became intrusive, and this was without any kind of noise reduction or gates in use. The frequency response of the unit is quoted as 16Hz-20kHz, and I certainly wouldn't challenge that: processed signals show clarity and brightness at the top end, with smooth well-defined bass. The effects available from each section vary slightly from one Configuration to another, but I'll deal with these differences in more detail when I describe those Configurations (patience, patience...).

The EQ section offers 3-band EQ (two shelving and one parametric band), 5-band (two shelving and three parametric), or 11-band graphic with one octave per band. For all bands, cut/boost is +/—14dB, and in the case of parametric bands the bandwidth can be varied from 0.20 to 2.55 octaves. The EQ section certainly allows for far more than a little tonal tweaking, to take the boominess out of an effect or make the reverb a little less harsh, for example - radical EQ is definitely on the cards.

The Pitch section offers Mono and Stereo Chorus, Mono and Stereo Flange, Pitch Detune, and Phaser. The Pitch Detune mixes a detuned signal (up to about half a semitone shift) with the dry signal, so it's rather like chorus without the LFO modulation. Flanging often seems to be the noisiest effect to produce in DSPs, and it does produce more noise than the other effects on the Quadraverb, though it's still a very acceptable level. I'd say it was noticeably quieter than the corresponding Multiverb effect. At this point, a comparison with the ART Multiverb is hard to avoid: both are similar in that they are multi-simultaneous-effects processors (I think I'd better invent a new acronym here: MSEPs, pronounced 'em-seps'), but the first significant difference in features comes in the Pitch section. Unlike the Multiverb, the Quadraverb does not offer a pitch shift option - on the other hand it has a cleaner sound, the flange being notably smoother.

Three basic types of delay are provided on the Quadraverb: Mono, Stereo and Ping-pong Delay. Ping-pong Delay places alternate echoes on opposite sides of the stereo picture. Mono is a 'straightforward' delay effect, and Stereo offers independent Delay time and Feedback for each channel. Delay times vary from one Configuration to another, but the Mono Delay is up to 1500ms in length, and the maximum Stereo and Ping-pong Delay is always half that of the Mono effect. It would be nice if the stereo delay was true stereo, but perhaps that would be expecting a little too much, given the price. Delay Feedback allows the number of repeats to be controlled, from one up to a maximum of about 30. Repeat echoes sound very clear - evidence of the use of 16-bit linear A-to-D and D-to-A conversion, and the Quadraverb's special new chip.

Reverb is perhaps the most important of the effects on offer here - it has after all given its name to the unit: I'm reviewing the Quadraverb rather than the Quadradelay or QuadraEQ. Room, Plate, Chamber, Hall and Reverse reverb algorithms are available, two of each: the choice between the two alternatives for each reverb type is not up to the user, rather it is determined by the effect Configuration. A good range of parameters is available for modifying the basic reverb effect - Pre-delay, Decay, Diffusion and Density (why do all reverb characteristics seem to start with the letter 'D'?). The decay of the high and low frequency parts of the reverb can be defined separately, thereby allowing the absorption characteristics of different acoustic environments to be simulated. A reverb gate is also available on all but the Reverse programs. Gate Hold Time, Gate Delay, and Gate Level (to which the reverb effect falls when the gate closes) can all be specified.

More important than these parameters, however, is the basic sound of the reverb, which is excellent. The 'wet' sound is clean and natural, though perhaps a little simple - this can be somewhat remedied by applying a short delay to the signal entering the Reverb section. Set to its maximum Decay, the reverb takes just under 20 seconds to drop below the threshold of audibility, a little longer for Plate and Room programs.

CONFIGURATIONS



The Configuration of the Quadraverb programs determines exactly how the signal path is routed through the four effects sections and to the stereo outputs. There are five possible Configurations, which allow varying degrees of complexity of routing: the general rule about how things work is that four (or fewer) sections are arranged in series. Each section can take its input from the output of the previous section, or from somewhere earlier down the chain, or perhaps use a mix of two sources. Each section's output can be sent directly to the Quadraverb's stereo output at an individual mix level, in parallel with that of the other sections, as well as providing an input for other sections. Each effects section has mono inputs only, so if a stereo effect is used as a source for the input to a second effect, that second effect will not realise the benefit of the first's stereo processing. The possible Configurations are:

Configuration 1. Quadmode: EQ-Pitch-Delay-Reverb.


- Quadmode: EQ-Pitch-Delay-Reverb.


In many ways, this is the most versatile Configuration. All four effects sections are used, and the number of combinations of possible effects verges on the mind-boggling - certainly not the kind of number you'd want to share a room with, if you knew just how big it was. True, many of those combinations might sound awful, but there's always a price to be paid for working at the cutting edge: experimentation is the name of the game.

The EQ section arranges itself as a 3-band EQ: High and Low shelving bands (10Hz-1kHz +/- 14dB and 2kHz-18kHz +/-14dB) with a fully parametric Mid band (200Hz-10kHz +/-14dB, bandwidth 0.2-2.55 octaves).

All Pitch effects are available in Quadmode, and the maximum Mono Delay time is 800ms: Stereo and Ping-pong Delays are half this. The input to the Delay section is switchable pre- or post-EQ. The Delay section has two inputs: input one is either pre- or post-EQ, and input two is taken from the output of the Pitch section. The balance between the two inputs is a programmable effects parameter. The Reverb section, coming as it does after the other three, has slightly more complex input arrangements. As with the Delay section, there are two mixable inputs. Input one can take its signal from pre- or post-EQ, Pitch output or Delay Mix input, and input two is either Delay Mix input or Delay output.

The output level of each effect section going to the stereo outputs is set in the Mix section: these output levels do not affect the signal level routing from effect to effect, so if you only want the output of the Pitch section to be heard via the Delay, so be it.

Configuration 2. Leslie-Delay-Reverb.


- Leslie-Delay-Reverb.


The Leslie section used here is in fact a kind of amalgamation of the Pitch and EQ sections. As the name suggests, it is a beautiful reproduction of the effect created by sticking your sound through a couple of rotating Leslie cabinets - a heady, vibrant swirl. For added realism, you can simulate the motor being switched on/off and run at high or low speed. The stereo separation can also be varied and, most fun of all, the motor speed may be controlled by a MIDI controller, such as the mod wheel on your synth. The accuracy of the effect is enhanced even further by the 'inertia' built into the motor - it actually takes time to speed up and slow down.

The Delay section is identical to the Quadmode delay, except that the input arrangements are a little simpler. Rather than describe the routing possibilities, I'll just say that they're essentially the same as for Quadmode, given that fewer sections are used, and refer you to the diagram.

Configuration 3. Eleven-band Graphic EQ-Delay.


- Graphic EQ-Delay.


In this Configuration, an 11-band Graphic Equaliser (16Hz-16kHz) is combined with a fully featured Delay - Mono Delay up to 1500ms, Stereo and Ping-pong up to 750ms. The 11 one-octave bands and 14dB cut/boost offered here make this a very powerful EQ section - it's a shame it isn't stereo.

- 5-band EQ-Pitch-Delay.


This offers better EQ than Quadmode, but at the expense of reverb effects. The Delay section offers full Delay time like the previous Configuration. The manual recommends this for guitarists who don't need the reverb, but it's obviously also a good Configuration for any instrument which requires some heavy tonal shaping combined with pitch effects and a full delay.

The EQ has High and Low shelving bands, as does Quadmode, but also has three fully parametric bands (20-500Hz, 200Hz-1kHz, 2k-18kHz, all with 0.20-2.55 octave bandwidth and 14dB cut/boost). These three bands make this EQ arrangement in some ways more powerful than the 11-band graphic; the 0.20 octave bandwidth allows frequencies to be emphasised or suppressed to be located and adjusted with great precision. It's very welcome to find such good EQ facilities on a device such as this: given that the Quadraverb is capable of producing other powerful effects at the same time, it could perhaps have got away with a mediocre EQ section and no-one would have really noticed. But as it is, the EQ is fully up to the high standards of the other effects sections.

Configuration 4. Three-band EQ-Reverb.


- 3-band EQ-Reverb.


This Configuration offers slightly different reverb types to all other Configurations. The Room, Plate, Hall, Chamber and Reverse reverbs are all just that little bit more subtle and complex. My personal favourite is definitely the wonderfully expansive Hall program, though the Chamber came a close second.

The Pitch section makes a minor reappearance in this Configuration in the form of a Reverb Chorus option - which is just what is says, a smooth chorus applied to the reverb.

FUN WITH MIDI



The other outstanding feature of the Quadraverb, besides its ability to produce simultaneous high quality effects, is its facility to allow up to eight of the effects parameters to be controlled simultaneously via MIDI controllers.

Possible modulation sources can be Note Number, Pitch Bend, Aftertouch or any other MIDI controller, and each target can be any of the continuous effects parameters (Delay Input Mix, Direct Mix Level, Effect Mix Level, Reverb Predelay, Reverb Decay, Mid EQ Frequency... there are about 50 others). This allows for a good deal of real-time performance control over effects, and therefore expressive processing! I've already mentioned controlling the Leslie motor speed with a synth mod wheel - other Leslie preset programs assign the speed control to Pitch Bend and Aftertouch instead. Other possibilities that open up include such goodies as using Aftertouch to increase reverb decay or delay feedback, or (a personal favourite) using the mod wheel to control the frequency of one of the parametric EQ bands - instant filter sweep from the front panel again!

All of these continuous changes to effects can, of course, be recorded into a sequencer, and subtle changes to effects can therefore be written into music in the same way that effects patch changes are commonly recorded. There's no longer any need for anyone to tweak a knob every time the end of a chorus comes around in order to, say, increase the decay time on a reverb effect - the change can be written into the same sequencer that the song is recorded on. The possibilities here are really for you to explore rather than me to explain, but there's certainly plenty of scope for controlling effects in detail, thereby making the use of effects more individual. This is exactly the kind of feature that the best effects units should be implementing these days.

One aspect of the processing that I would have liked to be able to control via MIDI, but could not, was the overall input level to any of the effects sections - this would have been just beautiful with a good long reverb. A minor point, and one that I've forgotten already, given all the other good things about the Quadraverb.

FOUR INTO ONE DOES GO!



ALESIS QUADRAVERB FEATURES

  • Up to 4 simultaneous effects
  • Real-time control of up to eight effect parameters via MIDI controllers
  • Stereo in and output (jacks)
  • Flexible effects routing
  • 90 preset effects stored in ROM, all fully editable
  • 100 user memories
  • 32-character backlit LCD
  • Touch-sensitive buttons
  • External 9 volt power supply (supplied)
  • 16Hz-20kHz effect bandwidth
  • 16-bit linear PCM conversion
  • 85dB dynamic range
  • £449 inc VAT

The problem with multi-function units of any kind, be they multi-effects processors or keyboard 'workstations' that combine the functions of synth, sequencer and drum machine, is that they often sacrifice a good deal of power and versatility in their various functions in order to integrate them. They become a jack-of-all-trades and master of none, not really performing any of their jobs particularly well.

This is certainly not the case with the Quadraverb; each of the four effects sections is very strong, both in respect of sound quality and the degree of variation in each effect. Nothing has been sacrificed in terms of the capabilities of each section in order to bring four into one. The Configurations allow a good deal of flexibility in terms of signal routing within each arrangement of effects, and the MIDI control facilities give the user considerable scope for real-time control over these effects.

Altogether, the Quadraverb has the kind of sound, spec and features that take it beyond the realm of merely a very good effects processor and on to being a truly creative tool.

FURTHER INFORMATION

£449 Inc VAT.

Sound Technology plc, (Contact Details).


Also featuring gear in this article



Previous Article in this issue

Steinberg Synthworks D110 Multi-Editor


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 - Mar 1989

Donated & scanned by: Mike Gorman

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