The Glue is an analog modelled compressor plug-in based on The classic 80's British big console buss compressor with some handy additional features. The compressor action is smooth and transparent as it uses the same high quality algorithms used in circuit simulators, but optimised to run fast. In addition to the regular compressor controls it has: Mix / Range / Sidechain High Pass knobs, External Sidechain support, Peak Clip, and Advanced Oversampling.

Powerful Oversampling
An unavoidable result of processing signals with a computer is aliasing. The Glue allows reduction of aliasing by any amount you want with very high quality oversampling filters. There are seperate settings for realtime use and offline renders. The recommended settings are x2 for realtime and x8 for offline render, but feel free to change these depending on the material and strength of compressions. As a rough guide, if you are compressing "dull" signals like bass guitars then you won't need oversampling. For brighter signals the default of x2 works well, and for very bright signals, or for agressive compression settings you may want to switch to x4 for realtime. You can also copy the current oversampling settings to all other instances of The Glue to quickly hear the difference it makes in your project - so you can either save cpu, or increase quality at the cost of more cpu easily. If you want high quality oversampling, but also want to have low latency then you can choose between the minimum phase (lowest latency) or intermediate phase (medium latency) instead of using the linear phase (highest latency). All oversampling methods produce an integer number of samples latency at DC, which reported to the DAW for correction, but for the best possible phase alignment of upper frequencies use the linear phase mode.

Classic VCA feed-back compressor
The Glue is an analog modelled compressor plug-in based on The classic 80's British big console stereo buss compressor. If used subtly on the main bus this produces gorgeously smooth and transparent compression that never goes out of style. When used heavily on a drum bus the classic "crack" of the attack portion of drums is produced, adding impact while controlling levels. The sidechain "detector" is a diode based envelope follower that "smooths out" the audio being sent to it. The detected amplitude of the sidechain input is used to to control the level of main signal, but is also sent to control the level of the input to the detector itself, in what is called a feed-back loop. This gives a different result to a feed-forward compressor, where the detector only changes the level of the main signal.

Diode Envelope Follower
Forming the core of the smooth behaviour of The Glue is an analog modelled dual diode envelope follower, which is solved using optimised nodal analysis. This results in the same results as using circuit simulation packages like SPICE, but with lower cpu overhead. Diodes are used as a way to smoothly switch between not attacking, and attacking, based on the level of the input signal level across the diodes. This means that very small input signals only result in slow attack times, and it's not until there is a large signal that the diodes conduct fully and you get the final attack time. This smooth transition is important for transparent compression, but it goes one level deeper than this because of the feed-back structure of the compressor. A feed-back compressor continually tries to "balance" the signal level being sent to the detector back to the point where the diodes switched off. This means that every change in detected levels is smoothly switched by the diodes, resulting in a very transparent and low distortion compression action. The circuit also features a dual diode setup, which results in a "soft mixmum", as the smoothed sum of both the left and right detected amplitude is used to control the stereo level. This is called "stereo linking", and results in no change in the stereo image, as both left and right VCAs use the same detected voltage to set their gain amounts.

Sidechain Highpass and Mix
If you want to reduce compression pump due to loud low frequency components the built in soft -6 dB/Oct high pass filter can be used to filter the signal being detected to de-emphasise the low end. Another way to reduce the audible results of compression is to use the Mix knob, which cross fades the dry input signal with the compressed signal in a phase accurate manner. Much like a level control the units on the Mix knob are shown in decibels.

Range
A new addition to the original circuit is the Range knob, which controls the maximum dynamic swing in changes of compression. The sidechain section of the circuit can easily be saturated with large input signals when the signal is clipped near the power supply voltage rails of the compressor. The main results in slewed attack times, because the top of the input signal being detected (not the main signal path!) is clipped away, so the detector is following a smaller signal. When set to full this control preserves the behaviour of the cleanest analog circuit, but the Range can be reduced slightly to emulate older units, or drastically for new creative control. The result is a useful alternative to parallel compression via the Mix knob.