As in the A-Z of Pro Tools K is for Katz, but in this case is isn’t the K metering system which is being discussed but the Precision K-Stereo Ambience Recovery plug-in. This plug-in is as simple as it is powerful. I really like it because instead of relying on some secret impenetrable digital voodoo, this process relies on delay, filtering, M/S matrixing and summing or subtracting signals. If you want to know how the process works you can read the patent online which explains it all.
It's important to understand that the main control, the Ambience control, is active at the 12 o'clock position. In fact this seems to be Bob's recommended setting. I assumed that 12 o'clock was flat and by turning it clockwise I would get more ambience (as indeed you do) and that by turning counter-clockwise I would get a reduction in ambience like the effect of Zynaptiq Unveil. This isn't how this plug-in works and fully counterclockwise would appear to be the flat position. K-Stereo doesn't reduce ambience.
As part of his 5 Unusual UAD Plug-ins You Should Really Consider, Mike covered the K-Stereo process in some detail. Over to Mike:
Developed in collaboration with renowned mastering engineer Bob Katz, the K-Stereo process is part of the UAD Precision series of mastering processors. What this processor does is quite clever. Using Mid/Side processing and elements of the Haas effect and other psycho-acoustic effects, the K-Stereo is capable of extracting natural ambiance from a mix to enhance the stereo depth of a track.
Ideal for mastering tracks that have been mixed “too dry” or need more space, the UAD K-Stereo is great at adding depth transparently. This plug-in has been a saviour many times when mastering for a particular producer I’ve been working with over the years who hates reverb. The K-Stereo is uncanny at adding natural depth without sounding processed however like many processors it has to be used with care.
The plug-in is composed of four sections starting from the top left and the Ambience Enhance, which is where the main process is added. It comprises a deep and wide buttons, which affect the stereo and the depth of the sound and central control, which sets the amount of processing.
To the right is a three-band filter with low-pass and high-pass filers and parametric mid section with bandwidth control which lets you focus the effect to a specific frequency band between 150Hz and 10kHz to focus on a specific band, for example to add more depth to a snare drum or vocals.
The Mid/Side gain section lets you affect the mono or stereo part of your track to narrow or widen your mix while the Left and Right lets you balance each channel individually to rebalance your stereo tracks.
The plug-in also comes with some great presets created by Bob Katz himself that can be used as great starting point and be tweaked to better suit the track. Going through the presets is also a great way to hear what this processor is capable of.
Inserting it on a stereo track and turning the ambience enhance mode will make the whole sound wider and deeper. The more pronounced, the more obvious the effect becomes and pushing it to the maximum clearly shows the principle behind this processor. In Wide mode the Left and Right tracks are delayed from each other creating the stereo width also known as the Haas Effect. This trick is often used to widen guitars. In Deep mode, with the ambiance enhance control all the way up the song becomes modulated by delay so my understanding is that the delay is caused in the mono component of the track being duplicated and delayed, causing the modulation. Returning to more sensible settings it is easy to hear the effects work and how these processes can add the depth and width so transparently. It is also apparent that the relation between delays on the mid and the sides are carefully calculated so that the delay in the mono and the sides start to conflict with each other.
The EQ section is extremely critical as it serves as a side chain to focus on the effect on a particular band. I often tend to use around the vocals and snare frequencies to add more depth and width without affecting the bass, or to add width to the cymbals.
It is possible to overdo it and often a setting that I think sounds good, will later reveal itself to be too much so it's always good to A/B with and without a few times and come back to it to make sure the process is not doing too much.
The Precision K-Stereo is a very niche processor that will mainly benefit mastering engineers but when a mix or group needs more depth or wider sound-stage it is quite possibly the best way to do so transparently.