In the post-console world, some of us lack facilities we used to take for granted. These ‘Latency Killers’ aim to plug one of the gaps...
Lavry are best known for their high-end A-D and D-A converters, but the company also make a small range of mic preamps, USB interfaces, and specialised digital and analogue signal processors. Amongst the last category are two all-analogue ‘latency killer’ products, the LK-1 and the LK-Solo. Both address the same operational requirements and work in the same fundamental way — the latter is a simplified, more compact version of the former.
The problem that these Latency Killers are designed to overcome is that of the inherent A-D/D-A converter and computer buffering delays, usually referred to as ‘latency’, which are imposed on a signal doing the round trip between a microphone or instrument source and the computer’s monitoring outputs. These delays, which can reach tens of milliseconds in some extreme cases, often cause significant performance problems with vocalists (and other artists) as they hear their own voice or instrument, both directly and delayed, through their headphones.
The solution in such cases, of course, is to monitor the source microphone or instrument signal directly, ideally before any digital conversion and definitely before the computer. To be practical, this direct source monitoring has to be combined with any required cue signals emanating from previously recorded tracks in the computer. Thankfully, most computer audio interfaces already provide this kind of functionality or, even if they don’t, the same thing can be achieved relatively easily with a small external mixer. However, neither of these solutions caters well for those that want to use high-quality external mic preamps and converters (rather than rely on an interface’s mic preamps, or use a full-scale recording console, which will have most of this functionality built in), simply because of all the additional electronics that conventional interfaces or mixers insert into the recording and monitoring chains — and that’s where Lavry’s Latency Killers come in.
Lavry’s two Latency Killer products are, fundamentally, high-quality headphone amplifiers with some clever integrated all-analogue signal-routing facilities. The larger LK-1 model is a 2U rackmounting device with two separate headphone amps, while the LK-Solo is a 1U half-width portable unit with a single headphone output — but both models accept two line-level recording inputs and two line-level cue-signal replay feeds from the DAW, all of which feed the internal headphone amplifier(s) via adjustable level controls.
The two recording inputs would normally be fed from external mic or instrument preamps, and inside the LK units these signals are split to feed two destinations: the latency-free direct-monitoring headphone output(s), and direct loop-through outputs for onward connection to the DAW, for recording via an external A-D converter or interface. The line-level cue inputs work in a similar way, accepting Cue replay signals from the DAW (via a computer interface or external D-A converter) and, once again, these signals are split to feed both the internal headphone amplifier(s) and loop-through outputs for onward connection to an external monitoring controller. The benefit of these loop-through outputs is to enable the Latency Killer hardware to remain connected into the DAW system without disrupting the normal recording and monitoring signal paths and workflows, even when latency-free headphone monitoring is not required.
The major difference between the LK-1 and LK-Solo, apart from their physical sizes and the number of headphone outputs, is that the LK-1 includes some additional functionality to integrate two external effects processors into the headphone monitoring. This facility is typically employed to provide ‘comfort reverbs’ only on the monitoring, although the connected effects returns can also be dispatched to the DAW for recording on separate tracks, if desired.
Lavry’s original Latency Killer, the LK-1, features an internal universal power supply that accepts mains voltages between 83 and 265 V AC, and provides two separately controlled headphone outputs on the front panel, along with combi XLRs for the two line-level recording input sources. The latter are also duplicated on the rear panel, but only one set can be used at a time. Also on the rear panel are connectors for the stereo DAW Cue inputs plus two stereo effects sends and returns. The headphone amps can accept up to 24dBu on the recording sources, DAW Cue and effects return inputs, while the effects send outputs provide up to +17dBu. Direct hard-wired loop-through outputs are provided for the DAW Cue inputs (to feed a monitor controller), the recording inputs (to feed the computer), and the effects returns (in case they need to be recorded too).
All of the rear-panel audio inputs are equipped with combi XLRs, and the source recording and DAW Cue loop-through outputs also have paralleled XLRs and TRS sockets. Although the headphone amp circuitry expects nominal +4dBu input levels generally, the amp sensitivity is automatically increased by 12dB if the recording source TRS connections are employed to accommodate nominal -10dBV sources (this is purely a monitoring adjustment though — the loop-through outputs reflect the unchanged input source level). In fact, none of the LK-1s controls affect the recorded signals in any way; they purely adjust the headphone monitoring and effects-send parameters.
Nine illuminated push-buttons dominate the front-panel, and these allocate the encoder knob to the various monitoring parameters. The buttons are blue most of the time, but turn green when selected. A mains power button is also present on the front panel. The large rotary encoder is surrounded by a ring of LEDs indicating the monitoring attenuation (0 to 66 dB), or pan setting for the currently selected source/output. The encoder step increments can be switched between fine (0.5dB) or coarse (3dB) when showing levels (toggled by pressing the encoder knob and indicated by separate coarse/fine LEDs). When adjusting Pan settings only the 13 LEDs from nine o’clock to three o’clock are used to indicate the L/R position.
Each of the two headphone outputs have independent master volume settings, adjusted by pressing the relevant button and twiddling the encoder knob as desired. The headphone signals are derived from a unity-gain mix of the DAW Cue inputs and both effects returns, to which are added adjustable-level feeds from the two recording input sources.
The two recording sources are each split to feed three separate destinations, and pressing the button for the relevant input allows its contributions to each one to be adjusted independently. The Main button accesses the level and pan (via the final two push buttons) of the contribution to the headphone mix. Similarly, the level and pan of the signal dispatched to each of the two effects send outputs can also be adjusted independently. In this way each recording source can access either or both external effects processors.
All of the unit’s level and pan settings are remembered after powering down, which may be a convenience or a risk, depending on your point of view. It certainly pays to check the various levels before putting the headphones on, since the amplifiers are very powerful and the different gain settings are not obvious at a glance. Two user presets of all settings can also be accessed simply by pressing and holding the encoder knob while simultaneously pressing one of the headphone buttons to store the current settings, or one of the recording source buttons to recall them.
Despite its compact size, the LK-Solo also features an internal universal power supply, which again accepts mains voltages from 83 to 265 V AC, but the power switch is integrated into the rear-panel IEC inlet on this model.
All audio connections are via quarter-inch TRS jack sockets (accepting balanced or unbalanced signals) and there’s no input-sensitivity switching for the recording inputs. The internal headphone amplifier (which has just the one output socket) can accommodate a maximum input level of +18dBu before clipping — by which time it is producing nearly 2W into 32Ω headphones when turned up fully, which is more than enough!
Although the DAW and monitoring audio connections are on the back panel, the recording-source signals (from external mic or instrument preamps) are connected at the front, and if only channel one is connected it feeds both sides of the headphone monitoring automatically (and both recording thru outputs too). With two recording sources connected, they each feed their own respective side of the headphones (and recording outputs) — there are no panning facilities here.
As with the LK-1, monitoring levels are controlled via a large rotary encoder and the set levels for each input are remembered even after powering down. However, the LK-Solo features separate input level adjustments for the recording source and Cue signals, rather than an overall headphone output level. To adjust an input level, the required source is first accessed using the ‘Adjust Select’ push button (LEDs indicate the currently selected source), and there are two operating-mode options (determined by holding the Select button down for five seconds). Mode one toggles directly between the stereo Cue and both recording inputs as a linked stereo pair, while mode two steps between the stereo Cue signal and each of the two recording inputs separately. A push button adjacent to the encoder knob labelled ‘Resolution’ toggles between either 0.5 or 3.0 dB volume increments, with a total adjustment range of 66dB. The current level for the selected input is shown on a bright three-digit display scaled from 00.0 (muted) to 66.0 (full level).
Connecting either of these Latency Killers to an existing DAW setup is trivially simple. For testing, I used an SSL VHD Pre preamp as the recording front end, and the cue signals and recording destinations were provided by the line outputs and inputs of an RME AIO PCIe interface. The monitoring outputs hooked into my monitoring controller in place of the Cue feed from the RME interface. Latency-free monitoring is then a simple case of balancing the recording input source(s) level against the stereo Cue signal and, in the case of the LK-1, adjusting the send levels for any connected effects returns.
Both units exhibited exemplary audio quality, free from noise and with a neutral and clean character. There’s loads of headroom, too — in fact, the maximum monitoring level is seriously loud with low-impedance headphones. I can’t imagine anyone will complain that they need more level from either of these units.
They may complain about the LK-Solo’s lack of encoder mode to adjust the overall monitoring level, though. Being able to adjust the cue and recording source levels separately is great for fine-tuning the balance between artist and backing tracks, but is frustrating when you only want to turn everything up or down a little. The LK-1 doesn’t suffer from this, as it has overall volume controls for each headphone amplifier.
Both the LK-1 and LK-Solo Latency Killers do exactly what they’re designed to do, and offer the exemplary audio quality we’ve come to expect of Lavry products: audio signals are completely unadulterated by passing through these devices, and the headphone amps are clean, transparent and unusually powerful. They don’t really offer anything that’s not already available in most computer audio interfaces (apart from, possibly, ear-meltingly powerful headphone amps), and you could achieve something with even more versatility using a high-quality line-only mini-console like SSL’s X-Desk or SPL’s Neos, but such solutions are as expensive, if not more so, and the LK-1 and LK-Solo provide convenient, elegant, high-performance, zero-latency monitoring facilities that are attractive and reasonably cost-effective for anyone using ultra-high-quality stand-alone A-D and D-A converters and external mic preamps.
I can’t think of another dedicated stand-alone latency-free monitor system like this, but a high-quality line-level mixer with onboard monitoring facilities, such as an SSL X-Desk or SPL Neos would meet the same need.
- Lavry audio quality.
- Straight-wire record and monitoring-path pass-thrus.
- Astonishingly powerful headphone amps.
- Internal universal mains power supply.
- The LK-1 adds useful comfort-effects integration features.
- No overall level control mode on the LK-Solo.
- Preset monitoring levels not obvious at a glance.
The LK-1 and LK-Solo are all-analogue and surprisingly powerful headphone amps providing zero-latency monitoring convenience for high-end discrete computer A-D and D-A interfaces.
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