sidechain linking techniques

How an audio compressor responds to stereo content depends largely on how the channel linking is implemented in the sidechain. This has a major influence on how the spatial representation of a stereo signal is preserved or even enhanced. The task of the compressor designer is to decide which technical design is most suitable for a given overall concept and to what extent the user can control the linkage when using the device.

In analog compressor designs, in addition to unlinked “dual mono” operation, one usually finds simple techniques such as summing both stereo channels (corresponding to the center of the stereo signal) or the extraction of the maximum levels of both channels using a comparator circuit implementing the mathematical term max(L,R).

More sophisticated designs improve this by making the linking itself frequency dependent, e.g. by linking the channels only within a certain frequency range. It is also common to adjust the amount of coupling from 0 to 100%, and the API 2500 hardware compressor serves as a good example of such frequency dependent implementation. For the low and mid frequency range, simple summing often works slightly better in terms of good stereo imaging, while for the mid to high frequency range, decoupling to some degree often proves to be a better choice.

The channel coupling can also be considered as a summation of vectors, which can be easily realized by sqrt(L^2+R^2). As an added sugar, this also elegantly solves the rectification problem and results in very consistent gain reduction across the actual level distributions that occur between two channels.

If, on the other hand, one wants to focus attention on correlated and uncorrelated signal components individually (both of which together make up a true stereo signal), then a mid/side decomposition in the sidechain is the ticket: A straight forward max(mid(L,R), side(L,R)) on the already rectified channels L and R is able to respond to any kind of correlated signal not only in a very balanced way but also to enhance its spatial representation.

More advanced techniques usually combine the methods already described.

TesslaSE mkII released

TesslaSE mkII – All the analog goodness in subtle doses

TesslaSE never meant to be a distortion box but rather focused on bringing all those subtle saturation and widening (side-) effects from the analog right into the digital domain. It sligthly colors the sound, polishes transients and creates depth and dimension in the stereo field. All the analog goodness in subtle doses. It’s a mixing effect intended to be used here and there where the mix demands it. It offers a low CPU profile and (almost) zero latency.

With it’s 2021 remake, TesslaSE mkII sticks to exactly that by just polishing whats already there. The internal gainstaging has been reworked so that everything appears gain compensated to the outside and is dead-easy to operate within a slick, modernized user interface. Also the transformer/tube cicuit modeling got some updates to appear more detailed and vibrant, while all non-linear algorithms got oversampled for additional aliasing supression.

Available for Windows VST in 32 and 64bit as freeware. Download your copy here.

RescueMK2 2.1 update available

RescueMK2 [Read more…]

utilizing early reflections in a production

A quite often underestimated or even forgotten production technique is to take advantage of artificial early reflections which could be added somewhere during the mixing process. Without inserting any fully fledged reverberation at all, applying such techniques allows to dramatically increase stereo width and depth perception as well as a way better instrument localization even in a busy mix. Creating density is not the goal here but the opposite is the name of the game: achieving a clear and intelligible mix.

In a simple case, one can place a short and plain delay (a slap-back echo) on a track and properly place it in the stereo field – maybe on the opposite side of the source but that’s just an example. More sophisticated tap delays could be used to create a sort of room experience and some reverberators are allowing to disable the late reverb diffusion and just to use their early reflection generation. There are no restrictions in general – allowed is what gets the job done in that specific mixing situation.

released: Rescue MK2 – analog style modelled signal designer


Rescue MK2 is the major overhaul of the analog style modelled signal designer already introduced back in 2007. It is a sophisticated mid/side based transient processing device which not only allows detailed ‘3D’ imaging control but also fancy transient compression and distortion with dynamics that remains vibrant and alive.

Changes at a glance:

  • Some internal routing changes are streamlining the workflow per channel.
  • Based on true stateful signal saturation algorithms, it provides way smoother transient management and distortion.
  • Better support for different gain-staging levels is introduced.
  • The analog style signal path emulation is a complete rework.
  • The manual is completely rewritten.

More and detailed information is included in the manual.

Rescue MK2Β  is a Windows x32 freeware release for VST compatible applications and you can grab your copy via the download page.

major mkIII update for Density bus compressor released

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announcing Density mkIII – providing depth and dimension, mastering grade

As hinted earlier in a facebook post, the TesslaPRO update will be delayed and probably released after the summer break – it is just not there yet. Instead, a major update for the Density compressor plug-in already made it and it will going to see the light somewhere later this month.

So, lets talk about the Density mkIII update. During the last two years or so I’ve received quite a lot of feedback to the Density mkII release – mostly coming from mastering engineers – on how to improve its dynamic response towards todays mastering needs. Some very early efforts did not made it but with the learnings from the ThrillseekerLA compressor design and the emerging stateful saturation approach everything was possible, all of a sudden. [Read more…]

how stereo works

Just in case you’ve ever wondered …


Density mkII – release date

Houston, we have a release date! The release of the Density mkII VST plug-in is now scheduled to end of this month. More specs and details will appear here during the next days or so – stay tuned. If you tend to react allergic concerning teasers better stay away a while from here πŸ˜‰

Density mkII – reworking the usage concept

Density mkII

Density mkII

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