Concrete Limiter module

Figure 468. Concrete Limiter.

Concrete Limiter is a transparent look-ahead brickwall peak limiter. It is designed to reduce peak levels without coloring the sound.

The purpose of ProChannel Concrete Limiter is to increase loudness as much as possible while preventing the signal from exceeding the maximum output level. ProChannel Concrete Limiter reduces the volume of the loudest parts (limiting), while simultaneously increasing the volume of the quiet parts (boosting). ProChannel Concrete Limiter is typically used as the final processor on the ProChannel strip, of tracks and buses.

In a typical mix of audio material, there are a few peaks that are much louder than the average signal. Increasing the overall volume would make these peaks exceed the maximum output level, causing unpleasant distortion in the music.

Limiting reduces the level of any peaks above the output “ceiling” so the average level can be boosted, thereby maximizing the volume and making the music sound louder.

You can think of audio limiting as forcing water through a funnel at higher and higher pressures. If you lower the Input Threshold too much, the funnel will eventually become full and the dense audio signal will distort.

The limiter is designed to operate transparently, only reducing peak levels without coloring the sound. Typically the loudness can be boosted between 6 dB and 12 dB without audible artifacts (such as distortion and pumping).

Limiting versus compression

A limiter is a simple dynamics processor, but is often overlooked or mistaken for a compressor. Both limiters and compressors apply gain reduction in order to attenuate transients and dynamics. However, they do so in different ways, which makes them suited to different situations.

Compressor. A compressor has a threshold control that specifies at which level gain reduction starts. A ratio control is then used to specify the amount of gain reduction to apply to audio that exceeds the threshold. This method is suitable for levelling and reducing the general dynamic range of individual instrument tracks such as vocals and drums.

Limiter. A limiter has a fixed Infinity:1 ratio, and typically uses an absolute output ceiling control, and the processed audio level cannot exceed this value. Limiting can be used in many ways, including:

Preventing the audio signal from exceeding an output ceiling value.

Creating a louder or fuller sound by limiting the dynamic range and increasing the perceived overall level of the mix.

Increasing the volume and density of individual instruments in the mix.

Preventing digital overs and other types of overload protection. Think of it as an audio safety net that puts a cap on the overall level. A limiter is the most transparent way to boost average level without clipping.

Creatively sculpting a sound’s dynamics.

Placing a limiter directly after a compressor to reduce peaks and even the overall level. This is especially useful when using a side-chain compressor.

Controls

Figure 469. Concrete Limiter controls.

A. Gain reduction meter B. Clipping LED C. ProChannel Concrete Limiter enable/disable D. Input Threshold E. Input meter F. Automatic Release G. Release Time H. Bass Boost I. Output Ceiling J. Output meter

The ProChannel Concrete Limiter module contains the following controls:

Clipping LED. Shows if the input signal to the ProChannel Concrete Limiter module is clipping. If there is any distortion in the ProChannel signal chain, the clipping LEDs let you identify where the clipping occurs.

Input meter. Displays the pre-processing signal level going into the limiter. The signal below the Input Threshold is orange and the signal above the Input Threshold is white. The maximum peak value is displayed numerically above the meter and as a white line, and can be reset by double clicking the number.

Gain reduction meter (GR). Displays the instantaneous gain reduction in dB. Gain reduction occurs when the input signal exceeds the Input Threshold. The maximum gain reduction amount is displayed numerically above the meter and as a white line, and can be reset by double clicking the number.

Output meter. Displays the post-processing signal level with clipping indication to warn when the level has gone above 0 dB. The maximum peak value is displayed numerically above the meter and as a white line, can be reset by double clicking the number.

Input Threshold. Sets the level at which limiting occurs. If the input signal level is below the Input Threshold, no limiting takes place. If the Input Threshold level is reached, limiting (i.e. automatic gain reduction) occurs, and the signal is amplified up to the Output Ceiling you have set. Only the signal above the Input Threshold is limited; all signal below the Input Threshold has a constant gain change that is controlled by the difference between the Input Threshold and Output Ceiling. Turning down the Input Threshold limits more of the signal, which will create an overall louder sound.The material becomes denser and less dynamic as the gain reduction rises. The valid range is -24 dB to 0 dB, and the default value is 0 dB. To adjust the level in fine increments, hold down the SHIFT key while moving the slider.

Output Ceiling. Sets the maximum-allowed (limited) level that can be output from the module. The valid range is -24 dB to 0 dB, and the default value is 0 dB. To adjust the level in fine increments, hold down the SHIFT key while moving the slider.

Release Time. Adjusts the time the limiter takes to go back to an inactive state after the input level has fallen below the Input Threshold value. Short release times will make the limiting more flexible and able to adapt to the input signal, but can cause fast changes in gain that may sound displeasing to the ears. Longer release times produce a signal with a more even level and less of a “pumping” effect, but make it harder to maximize the overall limiting because changes in the input level cannot be compensated for quickly enough to make the output volume totally consistent. The valid range is 1 millisecond to 2500 milliseconds, and the default value is 200 milliseconds. This is a manual setting that is overridden when Automatic Release is enabled.

Automatic Release. Enables program-dependent, automatic control of the limiter release time. The Release knob is disabled when Automatic Release is enabled. The release time affects the sound of the limiter. If the release time is too fast it can cause distortion. If the release time is too long it can cause “pumping”, or audible fluctuations of the volume. With Automatic Release enabled, ProChannel Concrete Limiter automatically selects the optimal release time based on the content of the music. If the music has lots of peaks, a short release time is selected; if the music level is steady and has few peaks, a longer release time is selected. Automatic Release provides maximum loudness without compromising quality.

Tip: When using a limiter in general, you typically want a very fast release time for transients and a slower release time for sustained energy (RMS) above the Input Threshold. Automatic Release mode automates the release time for you depending on the input signal.

Bass Boost. Allows a subtle degree of soft clipping, similar to a vacuum tube, on bass material before the final limiter to make it more pronounced and fatter. This allows more bass to pass through the transparent peak limiter on material containing low and high frequencies, without applying as much limiting to the low end.

ProChannel Concrete Limiter enable/disable . Enables/disables the ProChannel Concrete Limiter module.

Using the limiter

The ProChannel Concrete Limiter’s primary controls are Input Threshold, Output Ceiling and Release Time. Input Threshold controls how much gain is applied to the input to maximize the loudness. Output Ceiling defines the maximum level the limiter will output. Release Time controls how fast the transparent peak limiter responds to levels below the Input Threshold.

The most common problem caused by the use of a limiter is excessive distortion. This normally indicates that the limiter is active too much of the time (Input Threshold is too low). To correct the distortion, increase the Input Threshold and enable Automatic Release.

It is recommended that ProChannel Concrete Limiter be used as the final process after all dynamic and EQ adjustments have been made.

Typical workflow

1.	Insert ProChannel Concrete Limiter as the last ProChannel module on a track or bus.

2.	Right-click any ProChannel module header and make sure Post FX Bin is selected on the pop-up menu.

3.	Enable Automatic Release.

4.	Set the Output Ceiling control at the desired maximum value (0 dB, -1 dB, -3 dB, etc.) and play back the project.

5.

While listening to the project, adjust the Input Threshold control until the Gain Reduction meter indicates about 4-6 dB of gain reduction. The Gain Reduction meter responds whenever the Input Threshold level is exceeded by the input signal. As you reduce the Input Threshold level, the output level increases.

Note: Only the signal above the Input Threshold is limited; all signal below the Input Threshold has a constant gain change that is controlled by the difference between the Input Threshold and the Output Ceiling.

6.	Toggle the limiter enable control to compare the boosted signal with the unprocessed signal.

Tip: Use a compressor followed by a limiter. Since the limiter will protect you against any clipping distortion, you can use slower, more natural-sounding attack times on the compressor to keep the punch and impact of the mix. These won’t catch the fast transients but will control the “body” of the sound more gently and effectively. The limiter can then work much better and control all the fast transient detail – transparently.

Using ProChannel Concrete Limiter on a master bus

When used as the very last ProChannel module on the master bus, ProChannel Concrete Limiter will even out peaks and maximize the overall loudness of your tracks. Its purpose is to capture those peaks that a normal compressor misses.

When using ProChannel Concrete Limiter on a master bus, a good guideline is to insert a bus compressor with a high threshold and auto release before the transparent peak limiter. Then set the Output Ceiling of ProChannel Concrete Limiter to around -1 dB, with Automatic Release enabled. The goal is total transparency with no coloration or clipping of the sound, so use very subtle settings.

Tip: A good way to check your mix is by looking at the clip meter of the master bus compressor before the limiter. Make sure the overall mix of your tracks is not exceeding 0 dBFS before limiting. If it is clipping on the master bus compressor, group all the tracks together and bring them all down simultaneously until clipping does not occur.

Tip: If your mix will be mastered by another engineer, the best approach is to not overdo limiting when mixing. Keep in mind that the best possible sound is NOT the loudest mix.

Caution: Any limiter will damage the sound if you push it too hard. Used carefully, a great limiter can transparently shave off several dB from a mix without any audible side effects, especially if the original mix is dynamic to begin with. However, as soon as a limiter starts to cut into the body of the sound (anything that lasts more that a fraction of a second), its effects start to become audible and usually undesirable.

A note about peak levels

Use the following guidelines in order to avoid digital clipping:

Use the highest available bit depth (for example, 32-bit floating point).

When recording, allow at least -6 dBFS headroom (set maximum peak to -6 dBFS).

Note: ProChannel Concrete Limiter should not be used on a track while recording, as it has a look-ahead of 1.5 milliseconds and will result in a slight delay while recording.

During mixdown, set the max peak to -3 dBFS. Pay attention to both individual track meters and the master bus meter. Turning up levels on individual tracks has a cumulative effect on the master bus. If clipping only occurs on the master bus, you may only need to reduce the master bus compressor level. If it still clips, reduce the individual track levels.

When using ProChannel Concrete Limiter on a master bus, set the Output Ceiling to -1 dB at most. Any higher levels can result in clipping during down sampling, dithering and MP3 conversion.

 

See:

ProChannel

Using ProChannel

ProChannel modules and controls

PC76 U-Type Channel Compressor module

PC4K S-Type Bus Compressor module

QuadCurve Equalizer module

Tube Saturation module

PC2A T-Type Leveling Amplifier

Softube Saturation Knob

Console Emulator module

FX Chain module

Tape Emulator module

REmatrix Solo convolution reverb

GRIT (saturation) module

MAX (volume maximizer) module

SPACE (reverb/ambience) module

SMOOTHER (de-esser / de-harsher) module

GATER (remove noise) module

DEPTH (chorus / stereo shaping) module

PULSE (tremolo) module

SHAPER (transient control) module