Shure Level-Loc from Korneff Audio

Korneff Audio have been busy the past few months, working with both Shure and Tchad Blake on something very nice. A recent press release from Shure, as the 2025 NAMM show launched, indicates “Shure ‘Level-Loc’ Returns”. Tchad Blake, who is credited with popularizing the Level-Loc since he and Tom Waits discovered a used one at a gear swap in 1990, worked with Dan Korneff and Shure to model three hardware units, one that Dan has used for years, and two that Tchad uses, including the original box from 1990.



What is a Level-Loc?
Shure Level-Loc was first introduced in 1967 as part of a line of mixers aimed at live and broadcast audio. It was basically a high ratio “brick-wall” limiter used to quickly adjust gain so that the output level remained nearly constant as the input level varied. It found use in many venues where vocal levels needed to be evened out, such as PA systems in schools, churches and other halls that had people speaking who were untrained in mic use. By the late 1970’s PA systems had improved and started to include AGC (Automatic Gain Control) so the Level-Loc production was discontinued. But many of the standalone versions, including the M62V that Korneff have modelled, ended up in pawn shops, flea markets and at ham radio gear swaps.

One of these used units was discovered by Tchad Blake and Tom Waits while they were working on the Bone Machine album, and they took it back to the studio to see what it could do – and proceeded to blow out some of its circuitry! They managed to get it repaired and used it on the album, and Tchad loved the wild effects it could produce so much that he has used it on everything since. In the late 90’s Tchad was asked about “secret weapons” he used in the studio, and being an enthusiastic promoter of experimental sound processing, he described his use of the Leverl-Loc – even raved about it, saying it goes on every record he makes. So a resurgence of interest in the Level-Loc began.

Since Shure products are built like a tank (they pretty much use Mil Standards for environmental stresses including temperature extremes, humidity, shock and vibration – as you know if you have any of their mics) many of these units found their way into studios, and they just keep running. I see today some used, original 1960/70 hardware Level-Locs on the market for US$1,000 and up. I’d guess if you want original hardware and have more money than you need, a clean hardware Level-Loc would probably last as long as you, and maybe as long as your grandchildren!

But, if like me, you are trying to keep the studio clutter to a manageable level, and like the convenience of software tools, Korneff have you covered, in spades. This software emulation is very precisely modelled on real units, one that Dan Korneff owns and two from Tchad Blake. You can choose which unit you want to use with the small TB1, TB2 and DK buttons in the upper right of the GUI, and any one of them should satisfy anyone who wants to add some unpredictable colour (and distortion) to tracks, buses, and maybe a full mix.

Korneff Level-Loc
As you can see in the first image above, the Korneff emulation has a front panel like the hardware, with an Input Level dial, a Distance Selection switch, and a switch to apply or bypass Level-Loc. The Input Level should be obvious (but is not!), the Distance Selector is probably not obvious, and the Bypass switch does not bypass the full plug-in, as such a switch usually does! Starting with the bypass switch, it does bypass the limiter effect (Level-Loc) but leaves in the other electronics, including transformers. As you will see later, even with the Level-Loc section bypassed, there is still a lot of colour available as signal levels are pushed. And with Level-Loc bypassed, the Input level dial does not affect signal level through the other electronics! To push the signal level you can boost the signal you supply using your DAW, and you can further boost (or reduce) the signal using Input trim control in the lower left of the GUI. In Bypass mode I found THD (Total Harmonic Distortion) levels from well under 0.1% to over 10% are possible. And with the levelling engaged, you can get transformer distortion plus dynamic distortion beyond what you probably need.

What is the Distance Selection switch for? In a real unit it adjusts settings based on the intended mic placement, from close 6 inches or less, to a foot (12”) to 18” or greater. It basically changes the threshold in 6 dB steps, from the nominal -50 dB at the 6” or less setting, to -56 dB at 12” to -62 dB at 18” or greater. But see Some Details below – the effective threshold can be varied greatly if needed.

Below the hardware box image you can see Pre-Filters, Output Amplifier (gain), and Post-Filters. The filter controls are what they sound like, filtering the input signal as it enters the circuitry and filtering the processed output signal. The Output Amplifier control can boost the signal out of the levelling circuit up to 66 dB. It has no effect if the Bypass mode is used.

Above the hardware box image are three switches, Input Select (Mic or Line), Sidechain (Stereo or Dual-Mono), and Sidechain EQ. The Mic/Line selection changes gain into the circuitry, Mic boosting it 30 dB according to the user manual, although I seem to find 15 dB in testing. The Sidechain control selects between Stereo or Dual-Mono. Stereo applies the same gain control to left and right channels while Dual-Mono applies different gain levels if the signals on left and right have different levels, which is a mode I often use to add motion to audio. The Sidechain EQ is a useful control that applies EQ boost or dip to the signal sent to the sidechain control. From my tests this appears to be a bell-curve with a Q of 1, centred on the Frequency setting. And since this boost or cut is applied to the sidechain signal, boosting causes the threshold to be dropped while cutting increases the threshold level, but only for signals in the range of the frequency setting. Fun stuff! BTW, a real M62v Level-Loc is a mono device, so Korneff bring you two for the price of one! Actually much less than the going price of a used M62v.



Above the three switches the upper toolbar includes a Gain Reduction Display switch at the left, the Korneff “badge” in the middle, and the selection for one of Tchad’s M62vs or Dan’s as described earlier. The Gain Reduction Display, below, shows up as gray patterns behind the Input Select, Sidechain and Sidechain EQ controls and is a bit difficult to interpret. Might be nice to have a clearer image for this, maybe with colours, or as a separate window. Not critical and I didn’t find myself really using it.



Along the lower bottom, in addition to the Input trim dial, are controls for Oversampling, Presets, Dry/Wet ratio, and Output trim level. And there are switches for Tooltips, the user manual, redo/undo, general settings and a few other functions. If that were all, you could have a lot of fun with Level-Loc, but as with most other Korneff processors, clicking the Korneff “badge” near the top opens up a “back Panel” with controls for Input Impedance, Output Impedance, Release Time (of the compressor/limiter effect), and a power supply selector that offers Outlet (shows a US type power plug) or Battery. This last feature is wild – you can run the battery at its full 9 Volt level or drop it right down to dead. Along the way the distortion and dynamics change drastically.



The Release Time control allows you to do what required opening the hardware unit and using a soldering iron – you can change the R-C values (Resistance-Capacitance) which sets the release time of the compression/limiting effect when the signal level drops below the threshold. However, I found the suggested release time (R x C x 1000 in msec) is off by about 2:1, and what I measured was closer to release time = R x C x 500 msec. Of course you can use your ears to make a choice, but with all the other distortion and FR variations going on, release time may not be that critical. But it’s there for you to play with.

The Input and Output Impedances affect gain structure and EQ and although I made many plots of frequency and dynamic responses (I have over four dozen plots in my test folder) I won’t bore you with lots of graphics, but show a couple that display the changes in frequency response and dynamics with a number of different Level-Loc settings.



The above frequency response plots do not include use of the Pre or Post filter which can further roll off lows and highs.



The transfer function plots above show a 1:1 response from -100 dBFS to the threshold level as you expect with a limiter, except for one plot that shows about a 1.6:1 ratio below the threshold – this case uses a low battery setting of 4.2 Volts demonstrating how the battery can influence dynamics in odd ways.

Some Details
As the user manual (built into the Korneff Level-Loc as with all Korneff software – a very handy feature) states, the Level-Loc has a fixed threshold of -50 dBFS, internally. But since you can change the gain structure inside Level-Loc with a number of the controls, the effective threshold can be as high as about -10 dBFS and as low as -70 to -80 dBFS! I found the -50 dBFS threshold level is accurate when Input Select = Line, Input Level = 5, Level trim = 0 dB, Distance Selector is 6” or less, and Input Impedance is Low. Also the Power Supply should be set to Outlet or full 9 Volt battery (Output Impedance and other settings don’t affect the threshold). Of course, you may very well not care what the actual threshold level is, and as you can see from the animated plots above, there is a wide range of dynamics and frequency variation available when you vary the controls.

The Bottom Line
This is a fantastic sound mangler that can run from very subtle (especially using parallel processing via the Dry/Wet control) to just plain horrific! The 98 factory presets (I count 30 from Dan, 23 from Tchad, and 45 from Shure) can really inspire (or frighten!) you. And of course you can find some settings that do exactly what you want and can save them as user presets. Shure have been a major innovator of audio gear for over 100 years and the Level-Loc was an excellent device when it was introduced, and now is even more popular than ever. And the Korneff Shure Level-Loc is truly better than the original, even processing stereo signals as well.

Tech Data
Available for Mac and Windows as VST3, AAX, and (Mac) AU. Quad core i5 processor, 4 GB RAM. Mac OS X 10.14 or higher and Windows 7 & above. 64 bit DAW support only. Screen resolution 1024 x 768 or higher

In my test system (PC Audio Labs Rok Box PC, 64 Bit, 4-Core Intel i7-4770K, 3.5 GHz, and 16 GB RAM) Level-Loc used from 0.15% CPU resource (in Bypass mode) to 0.6% CPU (Bypass off) with no oversampling. If you are “into” oversampling, which makes no audible difference with all the dynamics and distortion that Level-Loc is capable of providing, then the CPU load increases at approximately half the oversampling ratio – that is 16x oversampling increases CPU load by about 8x, and 4x oversampling increases CPU load by about 2x. Actually an efficient oversampling implementation, but I found no need for it. Latency is 13 samples at any sample rate I tried (up to 96 kHz).

Pros
A “real” Level-Loc at a fraction the price of a 50 year old hardware unit.

More flexible than the real hardware with the ever present Korneff “badge” access to even more rear panel/internal controls.

Stereo – with both linked and dual-mono limiting capability which is beyond the original hardware.

Low CPU load and low latency unless you insist on oversampling.

Helpful built-in user manual and tool tips.

Approved by both Shure and Tchad Blake as providing a realistic experience (and beyond).

A heck of a lot of fun!

It's a Korneff product! Need I say more? Korneff listens to its customers and often adds features suggested by users.

And as I write this, it’s on an intro sale at half price until about February 20, which is a steal of a deal.

Cons
Not really any functional concerns – a minor graphics issue with the Gain Reduction Display being quite subtle!

A possible functional improvement is being discussed by Dan and some early users regarding the input trim – in the first release it affects both the dry and wet signal which can lead to significant gain shifts when the wet/dry ratio is changed. Dan is "on it" as always and will no doubt soon have an even better Level-Loc!

https://korneffaudio.com/product/shure-level-loc/