why the Thrillseeker compressors complement each other so well

Audio compressors use either a “feed forward” or “feedback” design to control the gain of an audio signal. In a feed forward compressor, the input signal is used directly to control the gain of the output signal. Essentially, the compressor compares the input signal to a threshold and reduces the gain of the output signal if the input signal exceeds the threshold. In a feedback compressor, the output signal is fed back into the compressor and used to control the gain of the input signal. So, the compressor compares the output signal to a threshold and reduces the gain of the input signal if the output signal exceeds the threshold. Both feed forward and feedback compressors can be effective at controlling the dynamic range of an audio signal, but they operate in slightly different ways and do have different characteristics in terms of their sound and response.

However, the specific sound of a device depends largely on other features of the circuit design and its components. For example, an optoelectric compressor uses a photoresistor or photodiode to detect and control the degree of gain reduction of the signal. But the make-up amplifier afterwards may contribute the most to the sound, depending on its design (tube or solid state). A variable gain tube compressor, on the other hand, uses a vacuum tube to control the gain of the compressor. The vacuum tube is used to amplify the signal, and the gain of the compressor is controlled by changing the bias voltage of the tube. This alone provides a very typical, distinctive sound that is very rich in harmonic overtones.

Both opto-electrical and variable-mu tube compressors are commonly used in audio production to control the dynamic range of a signal, but they operate in different ways and can produce different tonal characteristics. Opto-electrical compressors are known for their fast attack times and smooth release characteristics, while variable-mu tube compressors are known for their warm and smooth sound.

the beauty of opto-electrical compression – volume 2

When I was looking for a sophisticated stereo compressor for the outboard studio rack a year ago, I was surprised to see how many of the more interesting models now use opto-electric compression technology. Whether transparent or coloring, tube or solid-state amplifiers, transformer or transformerless, even two-channel layouts in mid/side encoding: far advanced compared to all the classic mono replicas.

Optical compressors are usually characterized by their distinct program-dependent compression behavior, mainly based on a physical memory effect in the detector itself. Other subtle nuances are found across the frequency spectrum that affect timing and curve characteristics, creating a complexity that cannot be reduced to simple two-stage controlled release curves, and which is the beauty of opto-electrical compression in its entirety.

Significant audio signal colorations, however, are shaped not by the gain reduction circuitry but by the make-up gain amplifier, whether it is tube or solid-state. Here, the audio transformer also plays an important role in polishing the transients and creating a cohesive sound.

ThrillseekerLA was designed from the beginning in 2012 as a modern stereo compressor with exciting sound coloring possibilities. It is a compressor with authentic opto-electric control behavior in feed-forward circuit topology.

The upcoming mkII update is a technical redesign dedicated solely to improving the sound. It delivers a unique box tone with thrilling bass and elegant top end void of any harshness in the mids. The compression not only glues everything together effortlessly, but also enhances the stereo image by adding depth and dimension.

The release is scheduled for mid-December.

bringing mojo back – volume 2

ThrillseekerVBL is an emulation of a vintage broadcast limiter design that follows the classic Variable-Mu design principles from the early 1950s. These tube-based devices were initially used to prevent audio overloads in broadcast transmission by managing sudden level changes in the audio signal. From today’s perspective, and compared to digital dynamic processors, they appear to be rather slow and can be considered more of a gain structure leveler. However, they still shine when it comes to gain riding in a very musical way – they’ve written warmth and mojo all over it.

ThrillseekerVBL is a modded version that not only features basic gain control, but also gives detailed access to both compression behavior and the characteristic of tube circuit saturation effects. Used in subtle doses, this provides the analog magic we so often miss when working in the digital domain while overdriving the circuit achieves much more drastic musical textures as a creative effect.

ThrillseekerVBL offers an incredibly authentic audio transformer simulation that models not only the typical low-frequency harmonic distortion, but also all the frequency- and load-dependent subtleties that occur in a transformer-coupled tube circuit and that contribute to the typical mojo we know and love from the analog classics.

new in version 2

Conceptually, the mkII version has been refined in that the peak limiting itself is no longer the main task but versatile and musically expressive gain control as well as a thrilling saturation experience. The saturation is now an integral part of the compression and is perfectly suited for processing transient-rich material. Both compression and saturation can be individually activated and controlled.

The circuit-related frequency loss in the highs has been almost eliminated and the brilliance control – originally intended just for compensation – can now also perform exciter-like tasks. The bias control has been extended to shape the harmonic spectrum in much greater detail by allowing the contribution of second order harmonics as well as the adjustment of the saturation behavior in the transient area of the signals. The transformer circuit has also been technically revised not only to resolve all the subtleties realistically but also to reproduce an overall tighter sound image.

ThrillseekerVBL has become a real tonebox, able to reproduce a wide range of tonalities. It provides access to the attack and release behavior and all compression controls can also affect the saturation of the signal, even when the compression function is turned off. This allows specific textures of signal saturation to be realized. As with the good old outboard devices, the desired sound colorations can be achieved just by controlling the working range. And if too much of a good thing is used, the DRY/WET control simply shifts down a gear.

To further improve the user experience some additional UI elements have been added giving more visual feedback. Although oversampling has been added, the actual cpu load was significantly reduced thanks to efficient algorithms and assembler code optimizations.

ThrillseekerVBL mkII will be released October 14th for Windows VST in 32 and 64bit as freeware.

TesslaPRO mkIII released

the magic is where the transient happens

The Tessla audio plugin series once started as a reminiscence to classic transformer based circuit designs of the 50s and 60s but without just being a clone stuck in the past. The PRO version has been made for mixing and mastering engineers working in the digital domain but always missing that extra vibe delivered by some highend analog devices.

TesslaPRO brings back the subtle artifacts from the analog right into the digital domain. It sligthly colors the sound, polishes transients and creates depth and dimension in the stereo field to get that cohesive sound we’re after. All the analog goodness in subtle doses: It’s a mixing effect intended to be used here and there, wherever the mix demands it.

The mkIII version is a technical redesign, further refined to capture all those sonic details while reducing audible distortions at the same time. It further blurs the line between compression and saturation and also takes aural perception based effects into account.

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

BootEQ mkIII released

BootEQ mkIII – a musical sounding Preamp/EQ

BootEQ mkIII is a musical sounding mixing EQ and pre-amplifier simulation. With its
four parametric and independent EQ bands it offers special selected and musical
sounding asymmetric and proportional EQ curves capable of reproducing several
‘classic’ EQ curves and tones accordingly.

It provides further audio coloration capabilities utilizing pre-amplifier harmonic distortion as well as tube and transformer-style signal saturation. Within its mkIII incarnation, the Preamp itself contains an opto-style compression circuit providing a very distinct and consistent harmonic distortion profile over a wide range of input levels, all based now on a true stateful saturation model.

Also the EQ curve slopes has been revised, plugin calibration takes place for better gain-staging and metering and the plugin offers zero latency processing now.

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

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.

The TesslaSE Remake

There were so many requests to revive the old and rusty TesslaSE which I’ve once moved already into the legacy folder. In this article I’m going to talk a little bit about the history of the plugin and its upcoming remake.

The original TesslaSE audio plugin was one of my first DSP designs aiming at a convincing analog signal path emulation and it was created already 15 years ago! In its release info it stated to “model pleasant sounding ‘electric effects’ coming from transformer coupled tube circuits in a digital controlled fashion” which basically refers to adding harmonic content and some subtle saturation as well as spatial effects to the incoming audio. In contrast to static waveshaping approaches quite common to that time, those effects were already inherently frequency dependent and managed within a mid/side matrix underneath.

(Later on, this approach emerged into a true stateful saturation framework capable of modeling not only memoryless circuits and the TesslaPro version took advantage of audio transient management as well.)

This design was also utilized to supress unwanted aliasing artifacts since flawless oversampling was still computational expensive to that time. And offering zero latency on top, TesslaSE always had a clear focus on being applied over the entire mixing stage, providing all those analog signal path subtleties here and there. All later revisions also sticked to the very same concept.

With the 2021 remake, TesslaSE mkII won’t change that as well but 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 now to appear more detailed and vibrant, while all non-linear algorithms got oversampled for additional aliasing supression.

On my very own, I really enjoy the elegant sound of the update now!

TesslaSE mkII will be released by end of November for PC/VST under a freeware license.

Getting the most out of the SPL Tube Vitalizer

In this article I’m going to share some analysis insights but also proposing an easy to follow 3-step approach for finding the sweet spot while processing any kind of material with this device.

Preparing for winter season: room heating with style

So, having now a Tube Vitalizer here on my desk (at least for some time), I was surprised about the lack of usable online reviews and background information. One just finds the usual YT quality stuff which might be entertaining in the best case but also spreads misinformation ever so often. To save those influencers honor it must be said that the Vitalizer concept is really not that easy to grasp and its quirky user experience makes it not easier. The manual itself is a mixed bag since it contains some useful hints and graphs on the one hand but lots of marketing blurb obscuring things on the other. Time to clean up the mess a little bit.

What it actually does

While easily slotted into the “audio exciter” bucket, some more words are needed to describe what it actually does. Technically speaking, the Vitalizer is basically a parallel dynamic equalizer with an actual EQ curve behaviour which aims to mimic equal loudness contours as specified in ISO226. Rather simplified, it can be seen as a high and low frequency shelving EQ to dial in a basic “smile” EQ curve but one which takes hearing related (psychoacoustic) loudness effects into account. It does this also by generating curves differently based on signal levels, hence the term “dynamic EQ”. And wait, it also adds harmonic content galore.

Taming the beast

To obtain an equal loudness contour the main equalizers center frequency must be properly set depending on the tonal balance of the actual source material. This center frequency can be dialed in somewhere between 1k and 20kHz by adjusting the Hi-Mid Freq knob which defines a cross-over point: while frequencies below that point gets attenuated, the higher frequencies gets boosted. However, this attenuation is already a signal level dependent effect. Opposed to that, the LF EQ itself (which actually is not a shelving but a bell type curve) has a fixed frequency tuned to 50Hz and just the desired boost amount needs to be dialed in. The LF curve characteristic can be further altered (Bass soft/tight) which basically thickens or thins out the below 100Hz area. Finally, this EQ path can be compressed now with the Bass Comp option.

A typical EQ curve created by the Vitalizer

On top of the main EQ path, the Tube Vitalizer offers an additional HF boost and compression option which both can be dialed in to complement the LF behaviour in a very similar fashion but in the high frequency department. Internally, both are in a parallel configuration and mixed back into a dry signal path. The according Process Level knob can be seen as a kind of dry/wet option but only for main the EQ part. The upper HF part is mixed back in separately by the Intensity dial.

Gain-Staging is key

For the EQ section as a whole, the Drive knob is the ticket for proper gain-staging. If compression can be dialed in properly for both compressors (as indicated by the blue flashing lights) input gain is in the right ballpark. One might expect to hear actual compression going on but it appears to be a rather gentle leveling effect.

Gain-staging for the output stage has to be concerned separately which might become an issue if the tube stage is activated and operates in shunt limiting mode. Now you have to take care about proper input levels since the Attenuators for both output channels are operating after the limiter and not beforehand.

Tube stage limiting: input (red) vs output (blue)

Which directly leads us to the additional harmonic content created by this device. First of all, there is always additional harmonic content created by this device, no matter what. One might expect the device to not show any such content with the solid state output stage but it actually does. The tube output stage just increases that content but signal level dependent of course and 2nd order harmonics are always part of that content. A serious additional amount of harmonics gets added as soon as the HF filter gets engaged by dialing in Intensity (and LC Filter mode activated!) but this sounds always very smooth and natural in the top end, surprisingly.

Delicious content

Also impressive is the low noisefloor for both output stage modes, tube and solid state. The first one introduces pretty strong channel crosstalk, though.

Workflow – Finding the sweet spot in 3 easy steps

Initial condition:

• Drive, Bass, Bass Comp and Intensity set to 0
• Device is properly gain-staged

1. Set Process to 5 and now find the best fit for Hi-Mid Freq for the given source material. For already mixed 2bus stuff you can narrow it down to 2-3kHz most likely.

2. Dial in Bass (either left or right depending on source and taste) and some compression accordingly.

3. Only then dial in some further HF content via Intensity and some compression accordingly. Adjust HF Freq so it basically fits the source/taste.

Workflow – Tweaking just one knob

My good old buddy Bootsy told me this trick which works surprisingly well.

Initial condition:

• Left most position: Bass
• Right most position: Bass Comp, High Comp, High Freq
• 12-o-clock position: Drive, Intensity
• Hi-Mid-Freq set to 2.5kHz

Now, just dial in some (few) Process Level to taste.

He also recommends to drive the input to some extend (VU hitting the red zone) using the Tube stage in limiter mode while always engaging LC Filter mode for HF.

interview series (9) – D.W. Fearn

Doug, when and how did you arrived in the music business?

I have had an interest in electronics ever since I was a kid growing up in the 1950s and 1960s. I built a crystal radio  receiver when I was 8 and my first audio amplifier (tubes, of course) when I was 10. I passed the test for an amateur radio license when I was 12 and that experience of communicating using Morse code was excellent training for  learning to hear. I built a lot of my own radio equipment, and experimented with my own designs.

The high school I attended had an FM broadcast station. Most of the sports and musical events were broadcast, and I learned about recording orchestras, marching bands, choirs, and plays. Friends asked me to record their bands, which was my first experience working with non-classical music.

Another major factor was that my father was a French horn player in the Philadelphia Orchestra. As a kid, I would attend concerts, rehearsals, and sometimes recording sessions and broadcasts. I learned a lot about acoustics by walking around the Academy of Music in Philadelphia during rehearsals.

It would seem logical that my musical exposure and my interest in electronics would combine to make the career in pro audio I have had for over 40 years now.

I was a studio owner for many years before starting the D.W. Fearn manufacturing business, which started in 1993.

announcing Thrillseeker VBL – Vintage Broadcast Limiter

Bringing mojo back – Thrillseeker VBL is an emulation of a “vintage broadcast limiter” following the classic Variable-Mu design principles from the early 1950’s. They were used to prevent audio overshoots by managing sudden signals changes. From today’s perspective, and compared to brickwall limiters, they are rather slow and should be seen as more of a gain structure leveler, but they still are shining when it comes to perform gain riding in a very musical fashion – they have warmth and mojo written all over.

Thrillseeker VBL is a “modded” version, which not only has the classic gain reduction controls but also grants detailed access to the amount and appearance of harmonic tube amplifier distortion occurring in the analog tube circuit. Applied in subtle doses, this dials in that analog magic we often miss when working in the digital domain, but you can also overdrive the circuit to have more obvious but still musical sounding harmonic distortion (and according side-effects) for use as a creative effect.

On top, Thrillseeker VBL offers an incredibly authentic audio transformer simulation which not only models the typical low-end harmonic distortion but also all the frequency and load dependent subtleties occurring in a transformer coupled tube circuit, and which add up to that typical mojo we know from the analog classics. This would not have been possible with plain waveshaping techniques but has been realized with my innovative Stateful Saturation approach, making it possible to model circuits having a (short) sort of memory.

Release date is not yet confirmed but most probably will be in May this year.