The UAD LA-2A Leveling Amplifier is a software dynamic compression plugin…
Table of contents
- 1. Description
- 2. History
- 3. Sound & Quality
- 4. Features & Controls
- 4.1. Input
- 4.2. Output
- 4.3. Attack
- 4.4. Release
- 4.5. Ratio
- 4.6. All Button Mode
- 5. Technical Details
- 5.1. Signal Flow
- 5.2. Input Transformer
- 5.3. Gain Reduction Design
- 5.4. Attack Characteristics
- 5.5. Release Characteristics
- 6. Best Practices
- 7. Famous Uses
- 8. Related Gear
- 9. Sources
The CLA-76 is a software emulation of the classic FET UREI 1176 compressor sold and marketed by Waves Audio. It is part of the CLA Classic Compressors bundle (CLA stands for Chris Lord-Alge – the legendary mixing engineer).
The CLA-76 has two versions which model two different versions of the original hardware compressor:
- CLA-76 Bluey models Revision B, also known as the Silverface Bluestripe.
- CLA-76 Blacky models Revision D, LN (Low Noise), also known as the Blackface.
Sound & Quality
Unlike Universal Audio's UAD 1176LN, the CLA-76 emulates not only the compression behaviour of the original hardware but also the distortion characteristics of the input transformer and output pre-amp. As a result, the CLA-76 can be used as a distortion box with compression turned off altogether.
The Bluey version tends to impart more aggressive compression and adds more character to the output. The Blacky version is somewhat more subdued and also has a lower noise floor (if the analogue noise circuitry is enabled).
Features & Controls
The CLA-76 has mostly traditional compressor controls: Input, Output, Ratio, Attack and Release. There is no Threshold control and the amount of compression is mostly driven by the Input control.
Adjusts the amount of gain reduction and relative threshold. In fully counterclockwise position, there is no compression and no signal level. Rotate clockwise to increase the amount of compression and input signal gain.
Adjusts the output level by up to 45 dB without affecting the amount of compression.
Sets the attack time between less than 50 microseconds (value = 7) and 1 millisecond (value = 1). Clockwise positions have faster attack.
Sets the release time between 50 milliseconds (value = 7) and 1 second (value = 1). Clockwise positions have faster release.
Five switches are used to select ratios of 20:1, 12:1, 8:1, 4:1, and All-Button mode. The 20:1 and 12:1 settings are typically used when peak-limiting is desired, while the 4:1 and 8:1 settings are used for general dynamic range compression.
All Button Mode
Also known as British mode or Hot mode, All-Buttons mode is a special mode of operating the CLA-76, originally discovered by accident on the hardware UREI 1176LN. The mode is enabled by pushing in all of the ratio buttons simultaneously (on the CLA-76 this is achieved by simply clicking on the All button). This changes the attack and release characteristics, as well as the compression curve, which contributes to a distinct, overdriven tone.
In this mode, the ratio is around 12:1, the release is faster, and the release curve changes. The attack value remains unchanged but there is a slight attack delay with low amounts of compression, a phenomenon sometimes described as reverse look-ahead, which allows preservation of transients despite heavy compression. The compression curve also changes to a pronounced plateau shape. The perception of distortion tends to increase with lower frequencies which is especially obvious on bass and kick drum sources.
- Michael Brauer on All Button mode (from Mixing, Recording, and Producing Techniques of the Pros, Second Edition):
- "...these four buttons makes it freak. The compressor needle, or indicator, will slam over to the right. Normally, whenever there is anything going on, the needle does the opposite. This looks really weird, but as long as it slams over this way, you know that it’s working. This setting gives the sound a certain sense of urgency. It strains it. It’s great for a vocal that needs extra urgency. Of course, you are going to be able to control the amount of strain in the voice by the input level. In the beginning, the needle may not move at all, so you have to keep bringing the gain up until the needle starts slamming over to the left."
The technical notes below apply to the original hardware UREI 1176 and will be of interest to the user of the Waves CLA-76 compressor.
The audio signal is first attenuated by the input transformer (the amount is controlled by the input control). Compression is then performed in the FET Gain Reduction section. Before the signal hits the output stage, it is sent to a sidechain Gain Reduction Control circuit where the voltage is fed back into the FET, controlling the amount of compression. Next, a pre-amp is used to increase the signal level. Finally, the audio signal is amplified through the Output Amplifier. The 1176 has a feedback circuitry as the signal level is determined after the gain reduction has been applied.
The 1176 incorporates a Class A amplifier based on a special mic-level custom-wound output transformer. The transformer converts between the unbalanced internal circuitry and the balanced external connections and provides the correct impedance matching. To compensate for the transformer's distortion and non-linearities, secondary and tertiary windings provide negative feedback from the output amplifier producing very low output distortion.
Gain Reduction Design
The 1176 has a Field-effect transistor design for gain reduction. Under this design, compressors use a special, high-impedance transistor which acts like a variable resistor to determine the gain reduction. The higher the voltage applied to the transistor's gate, the lower the drain-source resistance will be, i.e. the more gain reduction will be applied.
The 1176's attack can hit as fast as 20µS. This is enabled by the feedback design of the compressor's signal flow and the fact that signal detection happens at the output stage rather than the input stage. The attack is program-dependent.
The 1176 compressor employs a release mechanism which is heavily program-dependent. Faster release times are used immediately after transients to avoid dropouts. Slower release times are used in a continued state of compression, to reduce undesired pumping and eliminate the harmonic distortion caused by quick, repetitive attack-release cycles.
Start by choosing the desired compression ratio. Then adjust the Input control until the required gain reduction level is achieved. Next, adjust the Attack knob left to let transients pass through or right to squash them (with fast attack the 1176 is a very efficient limiter). Turn the Release control left to preserve the overall dynamic shape of the source or right to achieve more obvious compression and add distortion/grit to the sound.
All Button mode sounds best on single-track sources and is not typically well suited for bus compression. All Button mode works especially well on drum room mics, bass, aggressive vocals, and acoustic guitar.
- CLA-76 Bluey, Revision B version of this plugin.
- UAD 1176LN, another popular emulation of the UREI 1176 by Universal Audio.
- UREI 1176, the original hardware compressor.