interview series (11) – Andreas Eschenwecker

Andy, your Vertigo VSC compressor has already become a modern classic. What has been driven you to create such a device?

I really like VCA compressors. VCA technology gives you a lot of freedom in design and development and the user gets a very flexible tool at the end. I was very unhappy with all VCA compressors on the market around 2000. Those were not very flexible for different applications. These units were working good in one certain setting only. Changing threshold or other parameters was fiddley and so on. But the main point starting the VSC project was the new IC VCA based compressors sounded one dimensional and boxy.

Does this mean your design goal was to have a more transparent sounding device or does the VSC also adds a certain sound but just in a different/better way?

Transparency without sounding clean and artificial. The discrete Vertigo VCAs deliver up to 0,6% THD. Distortion can deliver depth without sounding muddy.

Does this design favour certain harmonics or – the other way around – supresses some unwanted distortions?

The VSC adds a different distortion spectrum depending when increasing input level or adding make-up. The most interesting fact is that most of the distortion and artifacts are created in the release phase of the compressor. The distortion is not created on signal peaks. It’s becoming obvious when the compressor sets back from gainreduction to zero gainreduction. Similar to a reverb swoosh… after the peak that was leveled.

Where does your inspiration comes from for such technical designs?

With my former company I repaired and did measurements on many common classic and sometimes ultra-rare compressors. Some sounded pretty good but were unreliable – some were very intuitive in a studio situation, some not…
At this time I slowly developed an idea what kind of compressor I would like to use in daily use.

From your point of view: To which extend did the compressor design principles changed over the years?

The designs changed a lot. Less discrete parts, less opto compressors (because a lot of essential parts are no longer produced), tube compressors suffer from poor new tube manufacturing and some designers nowadays go more for RMS detection and feed forward topology. With modern components there was no need for a feedback SC arrangement anymore. I think RMS is very common now because of its easy use at the first glance. For most applications I prefer Peak detection.

Having also a VSC software version available: Was it difficult to transfer all that analog experience into the digital domain? What was the challenge?

In my opinion the challenge is to sort out where to focus on. What influence has the input transformer or the output stage? Yes some of course. Indeed most of the work was going into emulating the detection circuit.

Which advantages did you experienced with the digital implementation or do you consider analog to be superior in general?

I am more an analog guy. So I still prefer the hardware. What I like about the digital emulations is that some functions are easy to implement in digital and would cost a fortune in production of the analog unit.

Any plans for the future you might want to share?

At the moment I struggle with component delays. 2021/22 is not the right time for new analog developments. I guess some new digital products come first.

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interview series (6) – Christopher Dion

Chris, you are the man behind the Canada-based Quantum-Music studio. What was your journey towards this venture?

My father (Alain Dion) was an internationally renown live sound engineer and technical producer (Nat King Cole, Sting, Celine Dion, Cirque du Soleil, and many locally-famous artists). Therefore, I grew up in an environment where high fidelity audio was the standard. My father hated everything that sounded less than perfect. Unconsciously, he trained my ears. I owe him a lot for that. Nowadays, every time we see each other, we spend much of our time talking about which compressors, consoles and techniques.

interview series (5) – Dave Hill

Dave, some of your Cranesong devices are already legend – how did that affair once started?

Before I started Crane Song I had been designing the Summit Audio Gear through and including the DCL-200, plus some gear that did not get finished. I was teaching electronics at a 2 year technology school at the start of the Summit thing and also was part owner of a small studio that had a 1” 8 track, and Ampex MM1000. The studio grew into what is Inland Sea Recording owned by me, which is a for commercial room with a lot of nice microphones and other gear.  It now serves as a design environment and has a number of customers that help keep it going.  Developing in a real studio environment helps make sure that what you are working on works correctly and sounds good.  When doing a session if one needs to mess with the gear it questions the design, but if you can turn a knob and it makes some thing sound good, it tells you something about the design.

major mkIII update for Density bus compressor released

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.

towards stateful saturation – very first audio shots

Around a year ago or so I’ve already started to look into a couple of stateful non-linear models which could be more suitable for a musical and convincing digital saturation experience. To make it even more harder, they should avoid the usual drawbacks such as huge latency or insane cpu consumption – if ever possible of course.

Meanwhile, my journey into the non-linear DSP land has made an important stopover with a first prototype implementation for such an approach, yielding a DSP core for musical harmonic distortion generation based on a stateful model. This opens the door for quite a number of interesting applications such as harmonic exciters or devices which needs convincing amp models whether thats a compressor output stage or even part of a guitar amplifier effect.

the beauty of opto-electrical compression

Opposed to VCA, Variable-Mu or FET based approaches, opto-electrical compression takes advantage of using a light-sensitive resistor and a small light emitter (a LED or electroluminescent panel) to obtain a gain reduction voltage in the sidechain path. This technique is well-known to add some smoother gain riding characteristics to the signal because of the specific attack and release response which comes from the inertia and inherent memory effect of the photoresistor element.

applying saturation through the sidechain

This short article gives a brief introduction on applying waveshaping algorithms not directly in the audio path but via a transformed equation through the sidechain and a VCA instead.

Typical saturation curves

compressor gain control principles

A short compendium on digital audio compression techniques.

Basic compressor configurations

Compression vs. limiting

Technically speaking the same principles are used in audio signal limiting and compression processors but just the transfer curves and envelope follower settings are different. Ultra fast attack rates and high ratio amounts are used for limiting purposes which causes just very few peaks to pass on a certain threshold.

In digital implementations limiting processors can be more strict due to look-ahead and clever gain prediction functions which guarantees that no peak information passes the threshold. That is called brickwall limiting then.