Operation

This section will progressively dive deeper into the details of the plug-in, explaining the specificity of each module. A complete list of the parameters exposed by the plug-in is available in the next section.

Setting Up the Transfer Curve

Changing the shape of the curve: thresholds, ratios and knees

At the heart of the dynamics processor is the transfer curve which shape can be controlled by the usual threshold, ratio and knee parameters. This curve describes the relationship (ratio) between the desired output level and the detected input level. This is where you choose what kind of effect (compression, limiting, gating...) you want to create.

The graph displayed in the Blue Cat's Dynamics user interface shows the ouput level as a function of the input level in dB scale. The controls offered to modify the shape of the dynamics response are explained below.

The up threshold and down threshold correspond to the upper part and lower part of the dynamics response curve. They let you specify the upper part (usually for compression) and lower part (usually for gating) of the curve independently:

For each part of the curve (above the up threshold and below the down threshold), you can choose the ratio, which corresponds to the ratio between the output and input levels. In the example above, an infinite to one ratio will be applied to the input signal as soon as it reaches -18 dB (hard limiting), and a 3 to 1 ratio will be applied as soon as it is below 40 dB (gate).

Once you have chosen the ratio, the knee parameter lets you soften the dynamics response. The difference between the left and right graphs below is 10 dB up and down knees:

Default response (knee=0)		Response with larger knee values

The effect is applied progressively, whereas with no knee the ratio changes as soon as the threshold is reached.

The depth parameter sets a limit to the amount of gain applied: it is by default set to infinite (no limit). If you decrease it, it sets the largest amount of gain reduction (or increase) that can be applied by the processor. Once this limit is reached, the processor stops increasing this amount.

Makeup and auto gain

When the shape of the dynamics response curve is changed, the max peak level and perceived volume will increase or decrease. That's what the makeup gain is for: compensate the gain loss or increase right after the main dynamics processor.

To simplify this task, you can use the compensate (auto-gain) feature that normalizes the response curve (0dB input produces 0dB output). The make-up gain is then applied after the normalization occurs. So beware that activating/deactivating the auto gain feature when make-up is used might result in a very large volume increase. Be sure to use the output limiter to avoid damaging your speakers or your ears.

Transfer Curve Shapes

Below are example of dynamics response curves for the various dynamics processing techniques described in the previous chapter.

Upper Curve

Changing the upper curve ratio and threshold lets you create a compressor (limiter) or an expander:

Compressor		Expander

Lower Curve

With the lower curve controls, it is possible to create a gate or an upward compressor.

Gate		Upward Compressor

The upward compressor can create interesting effects but can be problematic in the case of noisy input signals because it will magnify background noise. In this case you should either first apply a gate in your signal chain to get rid of this noise before or use the depth parameter to limit the gain increase.

Custom Shapes

One of the interests of Blue Cat's Dynamics is to create your own shapes that mix these usual behaviors to create custom dynamics effects. For example a combination of a gate and a compressor (that can be used to increase the loudness of a noisy signal), including depth setting to limit the gain:

Combined upper and lower curve settings

Time Response: Envelope Parameters

Now that the shape of the transfer curve is ready, you can adjust the parameters that drive the envelope follower (the component that computes the input level).

Blue Cat's Dynamics offers several envelope detection modes. Unlike most dynamics processors, it lets you choose to work in intermediate modes: using only a bit of opto-style envelope detection (feedback) is possible, as well as working with half RMS / half peak envelope computation.

Peak versus RMS

The Peak mode will detect transients (spikes) in the signal, whereas the RMS mode will measure the loudness of the incoming signal. Peak detection will be used to adjust the shape and dynamics response of the sound, while the RMS detection will usually be used to adjust the volume/loudness of a track.

VCA versus Opto

For the peak level, two modes are available:

1. VCA: the most common mode. It mimics the Voltage Controlled Amplifiers behavior
2. Opto: named after opto-electronic detectors with feedback (basically re-injecting the output signal for level detection). It uses a feedback loop and basically measures the envelope at the output of the compressor (instead of the input).

The Opto mode is usually smoother than the full VCA mode: in many cases it will sound a bit like the VCA mode with a longer release time. When you use very low attack and release times, you can smoothen the dynamics response by pushing the VCA-Opto knob.

Please note that with some particular dynamics curves, the 100% opto mode will not work nicely (for example with a very strong gate, 100% opto will never let any sound go thru).

Tip: when the plug-in is used with an external side chain, the opto mode can be a way to blend the detection on the external and internal signals. This allows for much more subtle effects that take into account both the external side chain and input signals.

RMS Envelope Parameters

The length (time) for the RMS envelope can be customized:

Increasing the RMS time makes it more stable but less reactive to loudness changes.

Peak Envelope Parameters

The Peak envelope detection has the usual attack and decay parameters plus an additional “hold” time that lets you specify how long the detector waits before it starts decreasing:

If all these parameters are set to 0, you obtain a wave shaper/distortion unit. We advise you to add a low-pass filter after the unit if you wish to keep a pleasant sound, and use at least 2x oversampling (1 stage) to avoid aliasing.

example of peak envelope response for a step input

For both the attack and release phases, an additional "shape" parameter is available. It changes the shape of the attack and release curves, globally preserving the slope of the curve. Positive values will basically increase the release time, the envelope decreasing slower and slower, while negative values will shorten the release time, the envelope decreasing faster and faster. The behavior is the same for the attack shape.

Below is an example of the resulting GR curve, using a brickwall shape for the dynamics curve.

shape=-100%		shape=0		shape=+100%

Tip: you will usually want to first adjust the attack and release time with shape set to 0, and when getting close to the desired effect, use the shape parameter to tweak the response (to make the dynamics processor sound slightly faster or slower).

Lookahead

With the lookahead control, you can delay the input signal (it introduces latency) so that the Dynamics plug-in reacts in advance to level changes. It can be particularly useful when using slow attack and release time, to make the response smoother.

Filters

The plug-in also includes two filters: one for the input signal (preamp filter), and one for the envelope detection (“side chain filter”).

Preamp Filter

The input filter is applied to the signal before entering the dynamics processing stage. A typical application is to cut lower frequencies before applying compression, to minimize distortion (lower frequencies will offset the input signal level). You can also use this filter for creative purposes.

The filter is automatically disabled when low and high cut frequencies are set to their default values.

Side Chain Filter

The side chain filter is used to choose which frequencies in the audio content trigger the effect. It is applied to the selected side chain signal (either after the input filter for internal side chain, or to the external side chain signal). It is not directly audible because it processes the side chain signal, only used to trigger the volume control.

Adjust the low and high cut frequencies to enable filtering, and click on the button next to the "SIDE CHAIN" title to listen to the filtered signal.

Side chain filtering can be particularly interesting when working with sounds that have a wide spectrum, such as full drums kits: you can trigger compression on the kick, cymbals or snare drum only by choosing the right cut-off frequencies, without affecting the input signal.

Stereo Control

The stereo version of the plug-in offer multiple ways to process stereo signals. This section shows how to fine tune the stereo behavior of the plug-in.

Stereo Mode

Choose between mid/side and left/right processing. In the default stereo mode (left/right) left and right channels are processed separately, and in mid/side mode, the plug-in processes the mid and side channels instead. Mid/side processing is described in the introduction section.

Later in this manual we will refer to channel 1 and channel 2 (respectively left and right or mid and side channels depending on the chosen mode).

Stereo Link

In order to keep the stereo balance coherent or on the contrary to modify the stereo perception of a track, you can choose to link the effect applied to each channel in several ways:

• none: no link. Each channel is independent. The stereo image may be strongly altered in this mode.
• average: mix the left and right (or mid and side) envelopes to compute the dynamics response. The same gain is applied to both channels.
• min: use the minimum of both envelopes to compute the dynamics response. The same gain is applied to both channels.
• max: use the maximum envelope to compute the dynamics response. The same gain is applied to both channels (default).
• flip: use the opposite channel envelope to compute gain. This increases the level differences of each channel.
• ch 1: compute the gain only with the envelope from the first channel only. The same gain is applied to both channels.
• ch 2: compute the gain only with the envelope from the second channel only. The same gain is applied to both channels.

Channels Activation

In addition you can choose to activate or deactivate the dynamics processing chain (from post preamp module to the dry/wet module) for each channel. See the little blue buttons on top of the stereo section.

It is possible for example to apply the effect only to the mid channel, and use the side channel as a side chain source (the source that triggers the effect). Several presets use this technique to modify the stereo image.

Oversampling

You can use Oversampling to reduce the aliasing issues that can be produced by the non-linear nature of the dynamics processor. It can be particularly useful for audio content with higher frequencies, or if you use large compression ratios with short attack and release times.

It is mainly applicable if you work with lower sample rates (such as 44.1 or 48 kHz). With higher sampling rates you will usually not need to work with an oversampled signal.

Beware that each oversampling stage consumes a lot of CPU (more than double CPU usage). You should use 4x oversampling with the stereo version for mastering purposes only, or with very low attack/release times in Peak mode. This is typically a feature you don't want to activate on every single track of a project.

Brickwall Limiter

The final stage of this plug-in is a brick wall limiter / soft clipper to avoid hard clipping and overshoot at the output of your host software. A common practice is to use a slow-attack compression stage and then apply the brick wall limiter for harder limiting on remaining transients.

The blue meter on the left of the output level meter shows the amount of limiting applied. The range of this meter is 60 dB:

You can also set the release time to zero. In this case the limiter produces clipping. You can adjust the softness of saturation using the Hard-Soft knob.

If latency is not a problem, the lookahead control allows the limiter to see peaks in advance and perform much smoother brickwall limiting with less distortion (recommended setting for optimal limiting: 10 ms).

Tip: it is strongly recommended to activate the brickwall limiter while experimenting with the parameters of the Blue Cat's Dynamics plug-in. The plug-in gives you great power to modify the dynamics of the incoming signal, which may result in huge audio spikes in some rare cases. The brickwall limiter protects your monitors and your ears against such mistakes!

Side Chaining

Blue Cat's Dynamics lets you use the signal from a track to control the volume of another. This technique is called "side chaining" as explained in the introduction. The plug-in offers three ways to do side chaining. You can choose the appropriate method depending on the capabilities of your host application and your specific needs.

"Traditional" Side Chain

The plug-in has extra audio inputs that can be fed by a side chain signal in most host applications (aka "external side chain input"):

To use the extra side chain signal, activate the external mode in the side chain box:

Note: for the VST version, it may be necessary to create a quad buss or group to be able to use the side chain input in some host application such as Cubase or Nuendo.

Once the side chain has been connected, it is possible to filter it (just like when using the internal side chain, i.e. the input signal) and listen to it.

Note: for the stereo version, using the mid/side mode does not affect the side chain signal - only the processed signal goes thru the dynamics processor in M/S mode.

Real Time MIDI Side Chaining

In addition to traditional side chain using the host application connection capabilities, it is also possible to use Blue Cat's Dynamics as a MIDI messages generator to perform real time side chaining. In order to use this feature, you need a host application that supports MIDI CC routing between plug-ins. You will also need to download the free Blue Cat's Gain Suite plug-ins.

The idea is that the Blue Cat's Dynamics plug-in is used to perform the envelope detection on the source track, and sends the volume control change messages to the gain plug-in that is instantiated on the destination track:

This can be achieved with the following procedure:

• Insert Blue Cat's Dynamics on the audio source track (the audio track used as control signal for the side chain) (mono or stereo).
• Setup the dry/wet parameter to 0% (all dry) so that the signal on the source track is not affected by the plug-in.
• Insert Blue Cat's Gain on the destination track (mono or stereo).
• Assign the Total Gain (or Total gain(1) and Total Gain(2)) output parameter(s) to a given MIDI channel and CC number.
• Assign the Gain parameter of the Gain plug-in to the same MIDI channel & CC number as the Total Gain parameter.
• Route Blue Cat's Dynamics MIDI output to Blue Cat's Gain (usually using a MIDI track, but this step depends on your host application).
• Setup the Blue Cat's Dynamics plug-in response curve and time constants. The source track controls the effect applied to the destination track.

If you have issues performing the above tasks in your host application, please visit our website and check our step by step tutorials

Note: in this mode, the output brickwall limiter is not used.

"Offline" Side Chaining / Gain Riding

If your host application does not support the methods above, or if you want to be able to tweak the gain reduction "by hand", you can use automation generated by the Blue Cat's Dynamics plug-in to drive a gain plug-in on another track.

You will simply need to record the gain reduction (or increase) as an automation curve and apply it to the other track. You can either use Blue Cat's Gain Suite freeware plug-ins or use your host gain automation feature.

The procedure if the following:

• Insert Blue Cat's Dynamics on the audio source track (the audio track used as control signal for the side chain) (mono or stereo).
• Setup the dry/wet parameter to 0% (all dry) so that the signal on the source track is not affected by the plug-in.
• Setup the Blue Cat's Dynamics plug-in response curve and time constants to obtain the desired effect.
• Insert Blue Cat's Gain on the destination track (mono or stereo).
• Arm the Total Gain (or Total gain(1) and Total Gain(2)) output parameter(s) to record it as automation curves.
• Play the track and record the automation envelope(s) on the source track.
• Copy/paste the envelopes to the destination track.
• Assign the envelope(s) to Blue Cat's Gain plug-in gain parameter(s) or to the destination track volume if provided by the host application.
• (Optional) Modify the automation curve to tweak the gain changes if required.

If you have issues performing the above tasks in your host application, please visit our website and check our step by step tutorials.

Note: in this mode, the output limiter is not used either.

Side Chaining Extended

The ability to use MIDI or automation for side chaining in Blue Cat's Dynamics lets you extend the traditional usage of side chaining: you can control any parameter of any automatable or MIDI controllable effect, not just gain!

As a result, you can use the dynamics response of a track to control any kind of effect on any other track!

A very simple and practical example: link the Blue Cat's Dynamics output with the gain of an EQ plug-in to instantly create a side chain dynamic EQ, as shown in this tutorial. Possibilities are endless, so we encourage you to experiment with your own effects.

By the way, if your host application supports it, it is also possible to control MIDI hardware with the plug-in: for example you can control the dynamics of an external hardware synth with a track inside your Digital Audio Workstation (DAW).

Tips & Tricks

Use Factory Presets

The plug-in is bundled with a couple of factory presets to help you get started. Because dynamics processing is highly dependent on the input signal, you will have to tweak the threshold and input gain values to adapt these presets to your own tracks.

Credits: factory presets created by Blue Cat Audio and Sink (www.sinkmusic.com).

Tweak the Time Response With the Shape Parameters

If you are getting close to what you expect but cannot reach the optimal attack or release setting by changing the attack and release times, you should probably start tweaking the attack or shape parameters:

Use attack and release shape to fine tune the time response

Attack seems a bit too short? Increase the attack shape parameter. Release sounds good but the tail of the effect is a bit too long? Decrease the release shape value!

Use a bit of Opto mode with External Side Chain

It can be interesting to use the vca/opto blend knob when using an external side chain in order to take into account both the external side chain and input signals. Since the "opto" style signal is computed at the output of the processor, it also takes into account the signal being processed.

Note: at 100% opto, external side chain signal is not used anymore, as it used only for the vca envelope computation.

Use Output Automation to Tweak the Effect

As explained in the Side Chaining chapter, it is possible to record the gain output parameter as an automation curve, and assign it to the volume of the track. This can be used to manually tweak the recorded automation to obtain the desired effect.

It is a good way to speed up automation writing: instead of manually drawing automation curves to perform custom manual dynamics processing (gain riding for example), the plug-in can generate the basic envelope for you which can then be optimized manually.

Use Output Automation to Monitor the Effect

Another application of the output automation capabilities of the plug-in is to monitor what exactly happens on a track: recording the "GR" output parameter as an automation curve lets you see directly on a track when the dynamics processor is doing something (gain reduction or increase):

Monitoring heavy compression on a kick drum track using automation in Pro Tools 12

Protect your Ears with the Brickwall Limiter

While tweaking the parameters of the plug-in and learning how to use the software, the output brickwall limiter should be always on.

This will prevent you from damaging your speakers or your ears. You can deactivate it later once you are happy with the settings and you can see that the limiter is not triggered.

Control the Gain With the Depth Parameters

If you want to keep control over the maximum range of the gain applied by the processor, you should adjust the depth parameter: it will ensure that the gain reduction or increase is limited! Separate settings are available for the upper or lower parts of the dynamics response.