Sonalksis SV-315 Compressor

Hi there! I am glad you keep on reading my stuff. Thanks upfront for your interest.

This time, as my assignment for week 4 of IMPMOOC at Coursera, I am going to show you my go to compressor plugin, the Sonalksis SV-315Mk2.

When opening the plugin, six main building blocks can be identified. From left to right these are display/monitor section, gain characteristic settings (top) and side-chain filter (bottom), level-detection curcuit (top) and limiter section (bottom) as well as the output section.

You can already conclude from the overview, that the Sonalksis SV-315Mk2 is not only a simple compressor but rather a two stage dynamics plugin combining a compressor and a limiter stage in a serial chain.

The display / monitor section is displaying the transfer function as well as the gain reduction that is applied to the signal. Furthermore it offers the possibility to directly adjust threshold, make-up gain and limiter threshold via ‘handles’ on the display. It has to be noted that the input level is monitored post side-chain filter, and is thus an accurate representation of the signal that is actually applied to the compressors gain element.


The next building block is the compression controls, featuring Threshold, Ratio, Knee, Auto Gain and Crush settings in the gain characteristics section, as well as Attack, Release, Auto, Hold and Compression Mode switches in the level-detection circuit.


As you will certainly know, Threshold sets the level above which compression is applied, Ratio controls the severity of compression, Knee defines the sharpness of compression onset and Auto Gain activates automatic gain compensation. Crush, however, is a characteristic feature of the SV315 that defines the gain reduction saturation point. Reducing the crush control effectively reduces the level at which the gain element saturates, therefore reducing the “crush” of compression on transients.


Transfer functions for high crush (left) and low crush setting (right).

A Crush setting of 100% will result in a compression of transients as fully as all other signals, as you can tell from the transfer function plot above. To avoid abrupt gain saturation Crush is dependent on the Knee setting. Knee itself is not restricted to fixed hard and soft knee settings, but can rather be controlled continously between 0dB (very hard knee) and 30dB (very soft knee). If, e.g., the knee is set to 20dB, the compression ratio will gradually increase from 1:1 to its set value, over a 20dB interval around the threshold level.


Hard knee (left) and soft knee (right).

In the level detection circuit the Attack and Release time can be set, Auto switches auto-release on/off while Hold holds the attack filter in place, i.e., it alters transient characteristics in the level-detection circuits. Higher Hold settings can create a more open sonic attribute in the compression characteristic. Furthermore, two attack/release circuits can be choosen from using the I/II switch, one with a vintage and one with a modern detection character.


The Side-Chain section offers the possibility to weigh the compression to be primarily triggered by a specific frequency range. The SV-315 offers a choice of four filter circuits, modelled on classic analogue side-chain filters. Unfortunately, Sonalksis does not provide specific information on the exact modells these filters are based on. Furthermore, one can also resort to an external side-chain by activating the Ext switch and following the routing procedure of the specific DAW.


The Limiter section enables control over an independent limiter, that sits between compressor and output-gain stage. The In switch turns the limiter on/off, Fast switches the release characteristic from slow to fast and Thresh sets the level above which limiting occurs.


Finally, there is the Output section consisting of a Power switch acting as a bypass control for the plugin, a meter monitoring the signal level at the output of the plugin, as well as a control to change the gain of the output level in order to compensate for compression. It is important to note that this output gain control is different from the make-up gain that can be applied via the blue handle on the display section or the Auto Gain switch. The former is applied post-limiter, while the latter is applied post-compressor but pre-limiter.


At the end I prepared some audio examples using the drum groove that Loudon Stearns provided in the course. The general settings, employing a rather high compression and a sharp knee, can be seen from the following picture.

example_settingsOnly the settings for Crush and Hold have been tweaked from 0 – 100% for the different examples. The individual settings can be identified via their soundcloud track name.

I hope that I was able to shed some light on my favourite compressor plugin and that you had fun with this post.
Again, thank you very much for reading my blog and for your valued input on this topic.

All the best,

[1] Sonalksis Ltd., SV-315 Compressor Operation Guide, pdf from (2009)

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