Allen & Heath Xone VF1

Photo: Mike Cameron

You probably know Allen & Heath as a studio mixer manufacturer, but they also specialise in high-end DJ mixing and processing. Now they have combined their studio and DJ expertise into a multi-mode analogue filter with sophisticated MIDI control.

For over 30 years, Cornwall-based Allen & Heath have built a solid reputation for making quality mixers. More recently they have diversified with the Xone range, tailored specifically for the needs of DJs. A logical extension to this range is the new Xone VF1, a compact 1U analogue filter capable of 24dB/octave mono or 12dB/octave stereo operation. The VF1 is an enhanced design taken from existing mixer circuitry and offers low-pass, band-pass and high-pass modes which can be selected in any combination. It also features a dual-triode valve with two separate elements, an LFO, an envelope follower, and MIDI control. With finishing touches that include balanced or unbalanced I/O, an internal power supply, and stylish clickless switching of functions, you'll probably agree that the market can cope with one more analogue filter.

Smooth Presentation

The matt-grey panel with its black text and Moog-style knobs conveys a tangible air of finesse. Four large switches are provided, which activate the filters and select the three filter modes. These switches are backlit in orange (for filter modes) and blue (for filter switching). With no audio clicks generated when you push them, they are exactly the kind of thing that inspires confidence.

Two large chunky knobs control cutoff and resonance. Smaller knobs set the rate and depth of the onboard LFO, and also adjust envelope-follower and overdrive amounts. Add switches for LFO waveform selection, envelope-follower decay, and the routing of envelope follower to overdrive, and you have a simple yet powerful set of options at your fingertips.

Where the front panel is a streamlined, ergonomic delight, the rear is as fully populated as Jordan's T-shirt! There are balanced inputs and outputs on both XLRs and TRS jacks, while unbalanced I/O is courtesy of phono sockets, although the TRS jacks happily connect to balanced or unbalanced gear. With the aid of a screwdriver, you can prod a tiny blue recessed button which sums the inverted filter output with the raw input to create cancellation effects. This inverted signal is then sent to the TRS jacks without affecting the signal routed to the XLR outputs. Versatility is the name of the game; accordingly, you can use all outputs at once.

When powered on, the orange glow of the valve is clearly visible through a grill on the top of the unit. The manual advises against obstructing this ventilation grill, so a little thought is needed in terms of placement in your rack. Thoughtful placement becomes an even more important issue when you realise that the rear panel has a couple of buttons on it. One of these, the Mono button, transforms the VF1 into a single-channel 24dB/octave filter. In this mode, the right input is ignored and the processed signal is sent to both outputs equally. Switching to a steeper filter slope adds extra depth and resonance — handy qualities for bass or solo instruments. Thus, positioning such a useful button on the back could prove jolly inconvenient on a piece of gear designed to spend its days in a rack or flightcase.

The other rear-mounted button is Local Off, which routes the front-panel controls via the MIDI processor. Don't worry that MIDI control involves any sacrifices; you can still use the large, friendly cutoff knob, for example, and the resulting filter sweeps are smooth enough for Local Off to be activated permanently. MIDI In and Out sockets are provided for transmission and reception of MIDI data. Perhaps we can forgive Allen & Heath for the lack of a MIDI Thru because, on such a densely-packed panel, you'd be hard pushed to find room for one! A further audio output — the stereo Monitor Out jack — is provided as a means of previewing the effect of the filter even when it's bypassed — ideal for live mixing situations. The IEC power socket and fuse holder round off this well-provisioned rear.

The rear offers inputs and outputs on both XLRs (balanced) and TRS (balanced/unbalanced) jacks, while unbalanced I/O is courtesy of phono sockets.Photo: Mike Cameron

In The Xone: Studio Listening Tests

Getting up and running is ludicrously easy, in part because the VF1 features no input controls or level indicator. This is a conscious decision on the part of Allen & Heath based on the philosophy that DJs shouldn't have access to level controls! With a unity-gain structure and a healthy +22dB of headroom, interfacing with most equipment should be a doddle. Indeed, I found the VF1 coped with a wide range of signals — keyboards, mixer sends/groups, and entire mixes — without complaint.

After making the audio connections and enabling the VF1 with the Filter On button, I set overdrive and modulation to zero, activated low-pass mode and played a chord on one of my digital synths. The filter has a range from 20Hz up to 20kHz, and a full rotation of the cutoff knob resulted in my jotting down terms such as rich, smooth, and sweet as my first impressions. Several weeks of daily use later, I'd classify the VF1 as ideal for enhancing a wide variety of material, never dominating in the manner of, for example, the Sherman Filterbank. Not that comparisons are really appropriate, but I believe the Xone VF1 would slot into a mix far more readily, and thus see more general use, than a filter with more 'attitude'.

A built-in Automatic Resonance Control automatically compresses the resonant peaks and reins in the sometimes speaker-shattering effects of high resonance, giving a pleasing sparkle without clipping, whistling, or loss of bass. This should definitely be a comfort when performing live. When the mono switch is activated, the effect of resonance becomes far more pronounced and you can stray into distortion. Here, the VF1 becomes more 'synthy', but remains one of the most predictable filters I've encountered. If this gives the impression of a lack of balls, any such suggestions are dispelled when you reach for the overdrive knob.

This block diagram in the VF1 manual shows how the different processing elements interact with the controls and I/O.

Valve overdrive with an analogue filter is a marriage made in heaven — well, any heaven that is famous for its pasties anyway! Low levels of overdrive introduce soft clipping, adding a subtle warming effect. At higher levels, hard clipping imposes a cutting distortion perfect for adding bite to solo instruments, basses, percussion... you name it! A make-up gain circuit is used to maintain a relatively constant level as you increase the overdrive amount.

For maximum tonal variety, any combination of the filter-mode buttons may be pushed simultaneously. For example, activating low-pass, band-pass, and high-pass produces an 'all-pass' filter that adds a gentle fizziness to any source as you crank up the resonance. low-pass and high-pass in combination create a notch filter, whilst high-pass and band-pass together conjure up a gorgeous, almost icy presence.

Having spent some time establishing a feel for the tone of the VF1, I increased the LFO depth, adjusted the modulation speed, and enjoyed some traditional filter warbles. Two LFO waveforms are available: triangle for smooth cutoff changes and square for alternating stepped effects. Modulation rates vary between 0.2Hz and 16Hz. The more experimentally-minded may wish for faster speeds, but in this context I feel the range is judged correctly.

The filter can also be modulated using the envelope follower, its amount set using a single knob. The envelope follower sets the response of the filter to input signal level; the higher the depth, the more the input will drive the cutoff frequency. A switch sets whether the envelope follower has a fast or slow decay; for loops or full mixes, a fast decay can give unusual artificial 'pumping' effects, but when used to filter synths, guitars, and so forth, a slow decay can sound more natural. A second switch determines whether the envelope follower will drive the output of the valve distortion. With dynamic sources this is very effective, adding a controlled overdrive effect that is responsive to the source transients.

Comprehensive MIDI Functionality

As shipped, the unit responds to MIDI channel 16. To change this, power on whilst holding down the high-pass button and then set the channel using combinations of all four buttons — a chart in the manual shows you how. The VF1 responds to MIDI Continuous Controller (CC) numbers 80-83, which govern the status of the filter mode and bypass buttons. Additionally, MIDI CC74 controls the filter cutoff. By sending these MIDI controllers, you can remotely access or automate key features via your master keyboard or sequencer. Helpfully, the buttons and cutoff knob all transmit as well as receive their respective MIDI controllers, but there is no way to control any other parameter, such as resonance or LFO speed.

However, that's not the full story of MIDI control. Additional functionality is available in the form of three additional MIDI input modes and, as when setting the MIDI channel, these modes require powering down to change. To do this, power up holding down the filter on/off switch and set the three available modes using the three filter buttons. When complete, normal operation is resumed by pressing the filter button again.

The three filter circuits in the VF1 can be combined to create a variety of unusual filter shapes, including an intriguing 'all-pass' response if all the filters are activated simultaneously.Photo: Mike Cameron

My only significant complaint about the VF1 is that it lacks a power switch, which means that resetting the MIDI input mode requires you to pull out the mains plug — not something I'd consider mid-performance, and I'm sure I'm not alone! The additional modes are useful enough for this to be quite annoying, and Allen & Heath have promised to investigate whether a future update could allow changes to be performed via MIDI.

Of the three modes, the first is designed to work in conjunction with the Allen & Heath's own Xone:92 DJ Mixer. I didn't have one of these, but was able to reproduce the MIDI controller messages it sends because the manual helpfully records what they are! In this mode, a single MIDI controller (CC13) is used to switch between filter types, although there are just five possible combinations available: low-pass, low-pass plus band-pass, band-pass, band-pass plus high-pass, and high-pass. This means you can't set low-pass plus high-pass or 'all-pass' using this method, which is a pity. When in this mode, CC12 controls cutoff and CC92 sets the filter on and off. I found the implementation of a single continuous controller very handy for switching filters, even given the restriction that not all combinations were accessible, but it was the other two MIDI input modes that were far more exciting.

When the second input mode is enabled, the filter cutoff tracks the pitch of incoming MIDI notes, provided that they are on the VF1's MIDI channel. You can therefore play a synth and process its output whilst using MIDI to track the pitch. Another fun technique is to direct MIDI notes to 'play' the filter whilst you're processing an entire track or mixer subgroup.

The last of the MIDI input modes is the 'keyboard mute mode'. This makes the current filter active only as long as an incoming MIDI note is held. As soon as all notes are released, the filter is deselected, resulting in no output. This is superb for gating effects — particularly when you trigger the mute function from devices such as sequencers or drum machines.

What's even better is that the MIDI input modes can be used in any combination — for example you could combine keyboard muting with keyboard tracking. In conjunction with your sequencer, this provides an endless source of freaky chopped-up mixes, with filters changing modes faster than your fingers could move. And all without glitches or annoying cracks and pops.

One final MIDI facility worth mentioning is that two VF1s can be linked together via MIDI to implement stereo 24dB/octave operation, both units being set to mono. Connect the MIDI Out of your first filter to the MIDI In of the second and the filter switches and cutoff frequency can be controlled remotely from the first. Nifty as this option may be, in most cases I actually found the 12dB/octave mode was just fine for stereo mixes; the 24dB mode seemed best suited to processing individual instruments.

DJ Dream Machine

From the moment I first unpacked the VF1, it screamed 'quality!' at me — and not just in terms of looks. Every sound source I put through it, from virtual analogue pads to drum loops and even full mixes, became more malleable and sonically gratifying. The effects on offer range from subtle and uncoloured to hard and overdriven. Low levels of overdrive add warmth, but at high levels a gritty underbelly of distortion is exposed.

Yet even at its extremes the VF1 remains usable and controllable; careful design wards off the harshness and squealing sometimes associated with analogue filters. As the envelope shaper can optionally drive the overdrive effect too, there's plenty of mileage in muckying up loops and samples. In fact, I'd say it's more or less obligatory!

Using MIDI control of gating, filter selection, and filter cutoff, there's a wealth of signal-chopping and swooshing activities to indulge in. Although not all parameters are MIDI controllable, the options chosen work well. Indeed, the VF1 has relatively few shortcomings, but its inability to switch freely between MIDI modes without pulling the plug certainly counts as one of them!

The keys to the VF1 are its simplicity and versatility — it just insists on being tweaked! To this end, the smooth knobs and soft switches are a delight and every feature seems to have a range of operation yielding only practical results. If you're looking for a stand-alone stereo analogue filter, the Xone VF1 comes highly recommended.