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Tips & Tricks — Precision K-Stereo Ambience Recovery Plug-In

Traditional recording wisdom states that the amount and quality of ambience, depth, space, clarity, and imaging in a recording can only be modified during the recording and mixing stage. Once you’re at the mastering phase, it’s hard to improve these characteristics without adding noise or distortion and muddying up the sound.

While there’s still no substitute for a great mix or good microphone technique, the Precision K-Stereo Plug-In is a simple yet powerful new ambience recovery tool that can actually enhance the depth and imaging of a recording during mastering without adding artificial reverberation or changing the ratio of center elements to side elements.

Here are some tips to help you get started with this great mastering tool for the UAD Powered Plug-Ins platform.

Getting to Know the Precision K-Stereo Plug-In

Let’s first take a listen to a few sound examples. The K-Stereo effect can be subtle, so it’s best to listen on headphones or studio monitors. You can also download these sound examples so you can A/B them in your DAW.

Here’s a hip hop example, first without the Precision K-Stereo plug-in:

Here’s the same example with the Precision K-Stereo plug-in engaged. Pay attention to the ambience on the snare and its spread in the stereo stage.

Here is a rock example from the band Glass Hammer before the Precision K-Stereo plug-in:

Overall, the effect of K-Stereo can be subtle. So, in this example, the K-Stereo effect has been cranked up so you can really hear what it's doing to the sonic depth and warmth of the stereo image. Bear in mind that that this setting is much more dramatic than you would normally would use in a mastering session: 

Using the Precision K-Stereo in Mixing and Mastering

The Precision K-Stereo Ambience Recovery plug-in is useful for fixing a variety of issues that can become apparent in the mastering stage. It can compensate for mixes made in poor monitoring environments where the resulting recording can sound too dry and small. Recordings that are missing front-to-back depth or have been truncated by improper recording and mixing procedures can also be enhanced and integrated to sound more organic.

The Precision K-Stereo plug-in can also reduce the congestion on dense stereo recordings, revealing inner details that were previously masked and giving more definition to individual instrument and vocal parts. It removes the artificial “edges” between the different spaces you’re trying to mix together, making recordings with multiple stereo microphone techniques sound more cohesive.

Lossy codecs, such as MP3 or AAC, can be compensated for with the Precision K-Stereo plug-in. If you are mastering a release for iTunes, inserting the Precision K-Stereo with a delicate ambience gain (somewhere between -4 dB and 0 dB) will create a “stretched” master that will yield better results than the original master when converted to an AAC file. Try this technique yourself; you can easily compare the stretched master with the original master using Apple’s free Round Trip AAC Audio Unit plug-in (part of their AU Lab application) or with the Sonnox Fraunhofer Pro-Codec on the PC platform.

In addition to mastering, the Precision K-Stereo plug-in can be used in other creative applications, such as on a stereo bus during mixing. However, since the process is optimized for broad spectrum mixes with at least some ambient content, the effect may be extremely subtle on individual tracks. The ambience recovery effect works particularly well on stereo recordings of instruments that have their own size and depth — such as pianos, drums, or vocals. Adding the K-Stereo effect on the drum or piano bus will bring up the room sound, producing a different quality than you might hear with an artificial reverb chamber.

Dialing in the Ambience

The controls in the K-Stereo Ambience Recovery plug-in are divided into four sections: Ambience Recovery, Ambience Filters, M/S Gain, and L/R Gain. The top-left Ambience Recovery section uses psychoacoustic principles to enhance a recording’s inherent ambience in a transparent, phase-accurate manner.

The Ambience Recovery section
controls the level of the K-Stereo effect.

The Ambience Gain knob controls the level of recovered ambience, with 0 dB being the typical setting one would use in a mastering setting. Feel free to turn it all the way up to experiment and hear an exaggerated ambient quality. This sound may be pleasant, but it’s probably too strong — ambience levels between -3 dB and +3 dB are most commonly used in mastering.

A setting of -4 dB is considered to be very subtle. It may be inaudible in a dense recording, but it may actually be obvious in simpler acoustic recordings that feature a string quartet or just a vocal with guitar. Don’t forget that you can click on the 0 dB label of the Ambience Gain knob to quickly return the control to 0 dB level, as with many UAD plug-ins.

The Recover button enables or disables the ambience recovery, while engaging the Deep mode provides the deepest ambience recovery. We recommend leaving Deep engaged unless you are looking for a more subtle effect.

Using the Wide mode spreads and enhances the shape of the ambience in the sides of the stereo picture. Generally, we like to leave Wide engaged as well, unless you are mastering small or intimate ensembles that sound too large when Wide is engaged.

Sculpting the Ambience with EQ Filters

The tone of the existing ambience in a recording can be adjusted using the Ambience Filter EQ section. These filters are not in the direct signal path as in a standard equalizer, but rather in the ambience signal path, making it a different brush in the mastering engineer’s palette. The low cut and high cut filters have a gentle, 12 dB/octave characteristic, while the midrange bell filter’s Q (bandwidth) can be adjusted from a very wide 0.5 to a medium-narrow 3.0.

Ambience filters sculpt the
K-Stereo effect.

The ambience filters may be especially helpful in leveling out the low and high ends of a recording. For example, if you lose some cohesion in the bass after turning up the Ambience Level in a rock and roll recording, adjusting the low cut filter will tighten up the bass. The midrange bell filter also can be used to brighten and add presence, which can be especially useful with vocals that need a better reverb color. The high filter is good for reducing splashy cymbals or the overall amount of percussion reaching the ambience signal.

Leveling Out the Stereo Field

The Precision K-Stereo plug-in features left and right channel gain, which can be used to make fine adjustments in channel balance or to raise or lower the overall level of the recording. You can also engage or disengage the L/R Gain button to bypass the gains for A/B comparison. Engaging the Link button makes it convenient to adjust overall gain without changing the stereo channel balance.

Use the M/S Gain section to
adjust the stereo image.

The K-Stereo process does not use M/S (Mid/Side) techniques to achieve ambience enhancement or recovery, however it does include a Mid/Side Gain section to help deal with imbalances within the stereo field. The best first option is to try and get the original mix engineer to remix the recording. If that’s not possible, the M/S section on the Precision K-Stereo plug-in can help polish the mix. Once you’ve made your adjustments, use the Ambience Level control to restore some of the ambience that may have been lost by manipulating the M/S ratio.

Manipulating the M/S balance isn’t very selective and if used too heavily it can cause the music to sound “phasey.” If you have to lower or raise the mid or side level by more than 1 dB, the cure can sound worse than the disease. So, if you need a more subtle M/S manipulation than the Precision K-Stereo’s full-band M/S Gain section can provide, more powerful M/S tools can be found in the UAD Brainworx bx_digital v2 EQ Plug-In, which can be used in conjunction with this plug-in.

Making the Judgment Call

In general, the Precision K-Stereo plug-in works well at any point in the signal chain. However, we recommend that any peak limiter should be the next to last process in the chain and dithering the last process. When performing noise reduction, put the Precision K-Stereo plug-in after the noise reduction processor in order to restore ambience which may have been lost during the process. 

The easiest way to judge the sound quality of the Precision K-Stereo plug-in is to bypass it by turning off the UA Power button, or by using the bypass system of your host DAW. Be prepared to experience withdrawal symptoms when the K-Stereo effect is bypassed. Since reverberation is usually a subtle effect, you may notice the K-Stereo effect first by its absence! It’s the kind of effect that you miss when it’s gone. On the other hand, make sure you aren’t using too much ambience gain; this can introduce unwanted artifacts, especially with percussive music. Educate your ear — ambience is an important and powerful element of any recording.


— Bob Katz

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