Clavia Nord Modular Virtual Analogue Modular Synthesizer, Part 1

Exploration

Reviews : Keyboard

CLAVIA NORD MODULAR VIRTUAL
ANALOGUE MODULAR SYNTHESIZER

Clavia's latest product is something else; an affordable modular hardware synth whose selection of modules and signal routing is user-definable in software, offering the synthesist staggering scope for sound design. In the first of this two-part review, PAUL NAGLE cross-modulates his Joy input with a Rapture envelope and goes into self-oscillating ecstasy...

The preview of Clavia's Nord Modular in February's SOS generated a surprising level of interest; before I had even received a copy of the finished mag, somebody had scanned my article and circulated it around the Internet! Why has this instrument generated such a buzz? Well, I think it's fair to say that it's a landmark in synthesis; a modular synthesizer whose constituent parts and signal routing are defined in PC-based graphical patch editing software -- and defined not by the manufacturer, but the end-user. The Nord Modular's 100 onboard patch locations can therefore store any potential synthesizer configurations you can dream up, and since this gives you more scope for synthesis than almost any synthesizer ever manufactured, you might find it proves to be the only analogue-style synth you'll ever need. (If all this talk of modular synths has completely lost you, check out the 'Spaghetti Junction' box on page 176.)

 

LET'S HAVE THAT ONE MORE TIME...

The signal processing architecture of the Nord Modular is essentially up to you; you are limited only by the capabilities of the modules Clavia supply with the instrument (one thing you can't define on the Nord Modular is the basic capabilities of the modules themselves). However, even this can scarcely be construed as a limitation, as new modules are being planned by Clavia all the time. Consequently, it's difficult to review the Nord Modular like any other synth, as so much is flexible or user-definable. What you therefore have here is the first instalment of a two-part review; this part examines the basic structure of the Nord Modular, the way the patch creation software works, and explains the function of the most useful modules. Next month, I'll give you a practical example of how to actually go about constructing a synth patch with the Nord Modular, look at some of the more involved features and modules in detail, and draw my conclusions about the instrument.

When reading this review, it's worth keeping a copy of my February preview handy, as it sums up much of what constitutes the Nord Modular in compact form, but for those who don't have this, a quick recap of the Modular's basic voice architecture is in order before I launch into a description of the synth's physical appearance.

"Why has this instrument generated such a buzz? Well, I think it's fair to say that it's a landmark in synthesis."

Clavia's previous virtual analogue tour de force was the Nord Lead synthesizer (see reviews in SOS May '95 and September '97), and one of the great strengths of this instrument was the way that patches could be layered or used multitimbrally. The Nord Modular borrows from this architecture, featuring four so-called Slots. Far from being physical holes in the synth, these are simply memory locations into which you load the patches you want to play. The Slots are accessed via the four Patch Group buttons labelled A to D on the Nord Modular's front panel (Patch Group is a term used interchangeably by Clavia for Slot). Together, the Slots can play a maximum of four patches at once (on different MIDI channels if required). Loading a Slot with a patch is as simple as hitting the desired Slot location button and selecting a patch from one of the 100 onboard memories. Once the Slots are loaded, you can select which one is active on the front panel using the Patch Group buttons.

As I mentioned in my preview, polyphony is not dynamically assigned; instead, at patch creation time, you request a certain number of notes for that patch via the software. Whether you get all these depends on both the number and the complexity of the patches in other Slots on the synth. Helpfully, the current polyphony is shown underneath the patch name on the synth's hardware LCD, and as you activate new Slots, you will see the polyphony figure update for each patch as the synth divides up the resources available to it.

MODULE MADNESS The Nord Modular currently offers over 80 modules to choose from, with more on the way; here's a list of them all. The different sections of the list relate to the tab headings under which the modules are grouped in the patch editor. As you can see, I haven't added notes on all of them, to prevent this review turning into a novel, but I will be looking at some of the more esoteric ones in part two of this review, in next month's SOS. IN/OUT MODULES * Keyboard Voice This module allows access to MIDI note, velocity and gate information for use as control values elsewhere. * Keyboard Patch As above, but information is taken just from the last note played. * Global The global clock sync module. You use this if you need to run several patches in sync. * Audio In * 1 Output * 2 Outputs * 4 Outputs * Morph More on this next month. * Note Detect This module outputs a gate signal if the designated note is received via the keyboard or MIDI input; it's good for performing actions based on a certain key. If several are ganged together, they can be used to react only on certain notes of the scale. OSCILLATORS * Oscillator A This oscillator has waveform selectors, coarse and fine tuning, variable keyboard tracking, adjustable pulse width with modulation input, two pitch modulation inputs, an FM input and a sync input. * Oscillator B This is almost the same as Oscilator A above, but has no pulse width control and no sync input, which makes a DSP resources saving of almost 3%. * Oscillator C This is a simple sine-wave oscillator, with a frequency modulation input. Cable together a few of these in a DX7 algorithm-style arrangement, and boom! your Nord Modular becomes an FM synth (only a much more flexible one)! * Oscillator Slave A-E As mentioned elsewhere, these are simpler oscillators which need to be linked to one of the three main oscillators, but which have their own intervals and modulation inputs. * Noise Generator * Percussion Oscillator This is quite a flexible little module, which produces a range of basic percussion voices, from bass drums to toms and right up to claves. ENVELOPES * ADSR Envelope Generator This is a standard Attack, Decay, Sustain, Release type, complete with a graphic display of the envelope shape. The envelope may be either logarithmic, linear or exponential in its response, and times range from a snappy 0.5 milliseconds to 45 seconds. Its output can be inverted at a push of a button. * AD Envelope Generator A much simplified Attack/Decay envelope. * Envelope Follower This module extracts an envelope from an audio signal. LFOs * LFO A A basic LFO module with its frequency shown in Hertz and a graphic waveform display. An enormous range of speeds is available, from a glacial one cycle every 699 seconds to 392Hz, and since the rate is modulatable, one LFO can affect another, speeding it up and slowing it down. * LFO B * LFO C * LFO Slave A-E * Clock Generator * Clocked Random Step Generator This outputs a new random value for each gate input it receives at the Clk input. The Col setting produces smoother changes between adjacent values. * Random step generator * Random Pulse generator FILTERS * Filter A * Filter B * Filter C * Filter D This is a filter with a 12dB-per-octave rolloff, with simultaneous high-, band- and low-pass outputs. * Filter E A switchable 12- or 24dB-per-octave affair which sounds much like the Nord Lead's filter. In addition to low-, band- and high-pass modes, it has a band-reject setting, complete with a display of the filter shape. Both cutoff frequency and resonance have modulation inputs. * Filter F Described as a Classic filter, this sounds as if it might be modelled on the filter Roland used in their modular systems. It is bright and switchable to 12-, 18- and 24dB-per-octave rolloffs. High resonance settings create a self-oscillation effect. This is a very cool filter indeed. MIXERS * 3-input Mixer * 8-input Mixer * Gain Controller Multiplier * Crossfade Controller * Pan Controller This allows you to place a signal anywhere in the stereo field; the position may then be modulated by a control signal. * On/Off switch * 4-1 switch * 1-4 switch * Amplifier AUDIO MODULATORS * Clip This is an onboard processing module which adds distortion to any signal passed through it. It really dirties up a signal; the precise amount of clipping can be modulated, and the Sym switch allows only the positive peaks of a signal to be clipped. * Overdrive * Wavewrap More on this next month. * Quantiser * Delay line * Sample and hold * Diode Processing This module can convert bi-polar signals to unipolar. Imagine, for example, an LFO which modulates pitch up and down; you would like to arrange matters so that it only bends pitch upwards. This is the module you'd pass your LFO modulation signal through to achieve your aim. * Chorus A pleasing stereo chorus effect with variable detune. * Inverter * Level shifter * Signal shaper CONTROL MODULATORS * Constant This produces a constant signal -- you choose the value. * Smooth * Portamento A * Portamento B * Note Scaler * Note Quantiser This module enables continuous control signals to be converted to discrete steps. A smooth pitch sweep from an LFO could be converted to a glissando. * Control Signal mixer LOGIC PROCESSORS * Positive edge delay * Negative edge delay * Pulse * Delay With a maximum delay time of 2.65 milliseconds, this can produce subtle phase-shift effects. Longer times can be achieved by patching several delays in series. * Inverter * Logic Processor Allows you to transmit a gate signal when two incoming signals meet a condition you specify. * Compare level * Compare A/B * Clock Divider Splits a pulse into a number of subdivisions by a factor which you determine. For example, you can run a sequencer at exactly twice the speed of another by inserting a divider. * Clock Divider Fixed SEQUENCERS * Event Sequencer A trigger sequencer. Each step has a switch which, if depressed, sends a gate signal. Each step can send two trigger pulses at two separate outputs. * Control Sequencer * Note Sequencer A * Note Sequencer B The sequencer modules are one area of the Nord Modular that deserve real attention; for me, almost by themselves, they thrust the Nord Modular to the top of my personal shopping list. As with sequencers in old hardware modulars, these can be used to sequence notes, filter settings or create any number of weird and wonderful effects. I'd love to spend an entire SOS review talking about these but sadly, space precludes me from doing so this month. Rest assured, however, that they will be examined in detail in part two of this review.

It is important to understand the way polyphony and patch complexity are irrevocably bound together: an unexpanded Nord Modular contains four DSP 'engines' and the rule is that no patch can exceed 100% of a DSP (the editing software shows the DSP load on a meter to help you keep track). All the modules you employ in building a patch use up a specific amount of the synth's total DSP resources, according to the module's functionality: for example, a fairly complex type of oscillator might use 11%, and a much more basic oscillator only 3.1%. Therefore you are always guaranteed a minimum of either 4-note polyphony (in a single Slot, with the other Slots deactivated) or four monophonic patches, running in four Slots. You soon adjust to the fact that simpler patches use less resources, and that, in practical terms, maximum polyphony is anywhere between 4 and 32 notes. An optional internal DSP expansion card doubles the available polyphony, but does not permit individual patches of any greater complexity.

 

RED BOX

Outwardly, the Modular is an unassuming red box with 18 freely-assignable knobs (plus one dedicated to master volume), an LCD, rotary data wheel and navigational controls. The keyboard version (reviewed and pictured here) has a 2-octave keyboard and transpose switches, but no additional performance controls. The rear of the synth sports twin MIDI In and Out sockets (no Thrus); one pair is intended for normal MIDI use and the second pair is used only by the PC patch editing software. The other rear sockets include four audio outputs, two audio inputs, a headphone output and connectors for a footpedal and sustain pedal. Construction is solid throughout; mains power is internal and supplied by a permanently-attached lead.

The 18 knobs may be assigned to any of the parameters that you choose for each patch (which is why they aren't labelled with function names, only numbers; the function of each knob is decided by you!). To me, it initially seemed illogical to number them in downward columns of three rather than from left to right, but there's a reason. As up to four patches may be active (in four Slots) at once, Clavia decided it would be useful to be able to tweak key parameters of each one simultaneously, and to this end, they created a Panel Split mode. If you glance at the panel layout, you'll see that the knobs are divided into four areas. When Panel Split mode is active, these areas correspond to patch Slots A to D, such that the first six parameters of Slots A and B, plus the first three parameters of C and D, can be edited from the knobs in the corresponding front-panel sections, no matter which Slot is currently selected. When not in Panel Split mode, all 18 knobs allow you access to the first 18 parameters of the patch in the currently active Slot.

To make best use of Panel Split mode, you need to be organised and ensure when designing patches that the most important parameters are assigned to the first six (for patches in Slots A and B) or first three (for patches in Slots C and D) knobs in each patch. I'll explain exactly how you go about assigning the knobs next month.

 

PATCH EDITING

I was initially sceptical about the idea of a synthesizer that tied me to a PC screen for editing until I actually loaded the supplied software; from that moment, I was a convert. The software is elegant, deserving the much over-used tag 'intuitive'. All actual audio processing (and subsequent storage of finished patches) is handled by the synth hardware, not the attached computer, so demands on your PC are light; essentially, if your machine can run Windows 95, you should have no trouble. Grab the demo version of the software from Clavia's web page (see address at the end of this article) if you are interested in trying it.

As well as for creating new patches, the editor provides a friendly front-end for other aspects of the synth's setup: MIDI channels, note and velocity ranges for the four Slots and the control of the System Clock which can be sync'ed internally or via MIDI (the Modular sends MIDI Clock if set to INT) More on MIDI and the Modular next month.

So, how does it work? Take a look at Figure 1 above. The various categories of module are selected via menus accessed from the tabs you can see in the top left corner of the editing window. Clicking on the tabs brings up a row of icons in the line below; each icon denotes a different module. Holding the mouse over a module icon produces a hint box which tells you the amount of DSP resources that module will use up. You add a module to a patch by simply dragging its icon onto the work area with the mouse.

As an example, Clavia currently offer three types of Oscillator: OscA, OscB and OscC (each with slightly different attributes). OscA has the most features and therefore requires the most resources (11%). When first dragged onto the work area, it appears as OscA1; if you need another OscA module for your planned patch, it will be assigned the name OscA2, and so on. Once in the main work area, modules can be moved around, removed again or renamed with a simple right-click (perhaps with a title that's more meaningful to you). After the modules you want are assembled, you must cable them together before you can hear any audio output, just as on an old hardware modular. Cabling is as simple as dragging the mouse from any module's output jack (square connectors) to any input jack (round connectors). Cables stretch (seemingly forever), and can be plugged, replugged, removed entirely or coloured for ease of recognition. The current version of the software (v1.10) even assigns a cable colour for you automatically according to function, although you can always recolour later if you wish. You can pick screen views which hide some or all of the cables with the aid of the Cable Color view selectors (in the top right corner of the patch editor window), or 'shake' your cables, so that they fall in different positions -- handy if your creation has become an unruly rat's nest and you've forgotten what's underneath.

Audio routing to and from the outside world is achieved via the on-screen representations of the Nord Modular's four hardware outputs and two audio inputs. As the list of available audio processing modules makes clear (see the 'Module Madness' box elsewhere in this article), the Nord Modular already offers some degree of internal effects processing, but Clavia's trump card is that if you want to patch out for a bit of reverb or a favourite effects patch, you can send the signal via a couple of the outputs, and return the processed signal via the audio input -- and you can do this at any stage in the signal chain. Too often, synthesizer effects comprise just a little reverb or chorus at the output stage, but this needn't be the case with the Nord Modular.

SPAGHETTI JUNCTION -- TRADITIONAL MODULARS The original, analogue modular synths of the '60s and '70s are voltage-controlled affairs comprising a series of synthesizer modules (oscillators, filters, envelopes, sequencers, and so on) with no hardwired signal path. Connections are made by cabling (or patching -- whence the word patch in modern synth terminology) together the different modules using wires with jacks at either end (patch cables). Understanding the different types of signals present is important -- for example, a note might be formed out of a gate signal (trigger) and a control voltage signal (pitch). The gate is typically used to trigger envelopes which control the duration of a note and the control voltage is routed to an oscillator to set the pitch of a note. However, the voltage-controlled nature of the old modulars gives them one advantage over digital synths -- because all the signals buzzing around a modular system are just voltages of varying strengths, you can simply add any sort of signal to any other sort of signal to produce or modify a sound -- so if you want to see what sort of musical note the voltage coming out of the sequencer module's clock produces, you can treat it as another oscillator by just patching it accordingly. This is not the case in a normal digital or MIDI-controlled synth setup, because controller information, such as MIDI volume, is different to note information. In order to get around this problem in the Nord Modular, Clavia have separated the components of a MIDI note, extracting note, note length (gate) information, key and release velocity, and made them available in the patch editor via the Keyboard Patch and Keyboard Voice modules (see the 'Module Madness' box elsewhere in this article). The information may come from either the last key that was played or from every key, and you are free to route these values to whichever parts of the synth you wish. Modular synths provide almost unlimited opportunities for signal routing and processing. This approach to sound design has its pitfalls, however; it's all too easy to set up a fantastic-looking routing that produces no audible sound whatsoever, which can, over time, lead to great frustration! Furthermore, reprogramming (ie repatching) a modular can involve a lot of recabling, which can be a time-consuming process, and an impossibility when playing live, such that many traditional modular users have had their on-stage musical direction imposed on them by their instrument. For the same reason, it's also impossible to effect instant patch changes, or store modular patches by any other means than actually writing down the necessary connections. For more detailed information on modular synths, check out Steve Howell's Exploring Analogue series, which ran in SOS from May to July 1994.

Four types of signal can flow between the modules that make up a patch. You can tell at a glance which kind of signal is emerging from or entering a particular connector from the colour of the connector (it is this that determines the signal type, not the colour of the cable plugged into it). The signal types are as follows:

* Audio (red junctions)
* Control (blue junctions)
* Logic (yellow junctions)
* Slave (grey junctions).

Audio signals, as the name suggests, are (to take three examples) the output from oscillators, noise generators, or any external audio signals being fed in. Audio is given priority in the system, and runs at four times the bandwidth of other signals (incidentally, internal processing is 24-bit at all times, so everything sounds clean and shiny).

Control signals are the equivalent of control signals sent by traditional modulars (see the 'Spaghetti Junction' box). This includes the signals from envelope generators, LFOs, sequencer modules, and so on.
Logic signals are basically on or off pulses used to trigger envelopes, drive sequencers, and so on.
Finally, Slave signals run down a special kind of connection used as a means of maximising processing power. Some oscillators are defined as Slaves; these are cut-down oscillators which must be connected to a Master oscillator in order to respond to keyboard pitch changes. The reason you would employ slaves is that they use up far less DSP resources than a Master oscillator.

The Nord lets you cable any output to any input, so that the types of signal, as on a traditional modular, are fairly interchangeable (see the 'Spaghetti Junction' box for more on this). For example, an Oscillator audio signal can be used as a control input for a filter or other oscillator, LFOs can be patched to an audio out or used as trigger inputs for envelopes, and so on, and so on. Just as on hardware modulars, you can experiment at your leisure!

Personally, I'd go so far as to say that this system would make a superb educational tool for the teaching of basic analogue synthesis principles and techniques. A particularly nice touch is the software's graphical representation of envelope shapes, LFO waveforms, and filter peaks (which change as you adjust the parameters of the filters, envelopes, oscillators and so on); this shows the degree of care Clavia have taken in making this more than just an imitation of a hardware modular synth.

Published in SOS May 1998