Phase cancellation can play havoc with your sound if you're using multiple mics, or combining mic and DI signals. This clever little box offers a solution, providing powerful phase-alignment facilities which go far beyond those of most mixers and preamps.
The Little Labs IBP (the initials stand for 'in between phase') is the solution to a problem that many of you may not even realise you have! It is a simple-to-use analogue phase-shifter that can be used either to realign two sources that are shifted in phase, such as a DI and a mic feed from the same source, or the two mics in a close/distant dual-mic setup. It works using a pair of symmetrical all-pass filters, which are conceptually similar to EQ except that they affect only phase, not frequency response. In fact the response of the IBP is flat to above 96kHz regardless of the phase alignment setting.
Physically, the box is little larger than a regular active DI (four will fit into a 1U rack tray) and it is powered via an included adaptor. It has balanced line ins and outs on XLRs and a further high-impedance instrument jack on the front panel. I would have preferred the ins and outs on balanced jacks for use with patchbays, but adaptor cables are fairly cheap. The rear panel houses the XLRs, plus two further jacks that provide a buffered version of the instrument output and an attenuated output (-14dB) for feeding back into a guitar amp for remiking. The high-impedance instrument DI input is provided for use with instruments such as electric guitars. It has a gain of up to 26dB (adjusted via a screwdriver trimmer on the rear panel) and a buffered output fed from before the phase shifter, enabling it to be used independently if required. A similar trim pot is used to adjust the reamped output level if required.
The front panel carries a row of six switches, plus a single rotary Phase Adjust control. Line/Instrument switching is handled by the first button, while the second provides a ground lift. The third button bypasses the phase adjustment circuitry for when remiking or conventionally DI'ing, and the fourth provides a phase invert function. Next is the button that sets the phase range to 90 degrees or 180 degrees (by selecting between one or two all-pass filters) while the last button sets the phase centre to high or low. This switches between a higher bandwidth mode (where one filter is used to cover the lower half of the audio spectrum and the other the top half) and a lower bandwidth mode that uses both filters to shift the phase of low frequencies, which, after all, is where most audible phase problems occur.
Whenever we cover a recording technique that uses two microphones (or one mic plus a DI), we usually suggest switching the phase of one of the signals to see which combination sounds best. That's because phase differences between the two signals will cause some frequencies to cancel and others to add (rather like a flanger with the sweep turned off, but less dramatic), and in most cases, the position that gives the greatest amount of bass is the one where the phase of the two signals is closest. However, this only provides you with a choice of two phase options. To get the optimum combination, you really need some way to fully vary the phase of one of the signals over a full 360 degrees. Delaying one of the signals by small increments of time can get close to achieving this, but as phase shift is frequency dependent and can be further modified by EQ settings, guitar cabinet speaker frequency responses and so on, an analogue system that shifts phase rather than time can often give a subjectively better result.
Typical situations where such a device would come in useful include drum miking, where there is inevitably a phase difference between the close kick-drum mic and the same drum picked up in the overheads, guitar amps miked with one close mic and one mic at a distance, and of course bass guitar, where it's quite common to combine a mic with a DI taken straight from the guitar or amp. Because the IBP has a phase invert switch and two range settings (90 degrees and 180 degrees), it can complete a full cycle of phase shift, allowing you to fine-tune the sound by ear while adjusting the amount of phase shift. What you should notice is the bass end coming into 'focus' with both depth and clarity. Using delays or EQ, you may get the same depth of bass, but it will probably sound less tight. Note that a device such as the IBP is only of any use where two signals are being combined — if you phase-shift a single signal in isolation, there will be no audible change.
The manual suggests letting the unit warm up for a while to allow its internal DC voltages to stabilise, after which it is ready for use. In my test setup, I used a small guitar combo with one mic right up against the speaker grille and the other about eight feet away. Both were mixed and adjusted to contribute similar levels, then the phase of the distant mic was adjusted using the IBP box. The subjective result is a little different depending on the Phase Centre Hi/Lo switch setting and you may also need to switch in the phase invert and the 90 degrees/180 degrees switch to home in on the area you're looking for, but what you hear as you adjust the phase knob is not unlike the phase effect you get from an analogue phaser pedal (which isn't surprising, as these also work by applying analogue phase shift to one signal). This provides a whole range of guitar tonalities from the same mic setup and amp settings, and the 'most in-phase' setting isn't necessarily the best artistically. In reality, you simply adjust the phase shift until the combined signal sounds the way you want it and then leave it at that.
Furthermore, because the input is at line level, you can use the processor during mixing wherever you have multi-miked sources, simply by inserting it into one of the mic channels on the mixer. Not only is this technique useful on multi-miked guitars, basses, or drum kits, but it can also improve the sound in situations where high levels of spill are inevitable, such as when recording acoustic guitar and vocals at the same time. In this case you can adjust the phase of either mic until the combined sounds are at their best.
The Little Labs IBP is a well-designed little box with plenty of headroom and a relatively simple user interface, though there is an even simpler version available (the IBP Junior) which dispenses with the instrument input and ground lift. Those with computer studios who use mainly samples may have little need for it, but anyone multi-miking electric guitars, drum kits or other sources should find it extremely useful, not least because it lets you experiment with the sound without having to keep moving microphones. My only criticism is that the manual is a little short on practical help, and concentrates instead on testimonials from satisfied professional users. However, if you've read the rest of this review, you should now have an idea of how to use the IBP, and it really isn't difficult to get impressive results from it.
- Makes it much easier to get a good sound in dual-mic setups.
- Well built, with plenty of headroom.
- The manual is long on user testimonials, but a little short on practical help.
A specialised, but very practical, processor for solving phase-cancellation problems in a musical-sounding way.
IBP £399; IBP Junior £299. Prices include VAT.
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