Our friends from “The Effector Book” (Japan-based guitar pedal aficionados) interviewed Strymon’s co-founder, Gregg Stock about their amp modelling pedal: Iridium. If you’re into the technicals and want to know a little more about the design process and philosophy, this might be the read for you...
Effector
When I first tried Iridium, I was surprised because it didn’t have the feel of typical ‘digital’ equipment; I’d say it didn’t even feel like a typical effect pedal! I have checked the sound through a mixing console and it actually feels like you’re playing through a tube amp if you close your eyes. How did you manage to eradicate artificiality and exaggeration? What’s the technical background?
GS
There are multiple advancements in Iridium that lead to the natural dynamic feel. The input signal passes through a discrete Class A JFET analog gain stage that is digitally controlled through the Drive knob. This allows for a dynamic interaction with your guitar or pedals before the signal is passed on to the signal processor. Our Matrix Modeling precisely recreates the proper response of the amplifier stages. We employ advanced non-linear techniques for multi-stage power sag and speaker distortion. The amplifier output runs into the highest quality Impluse Responses (IRs) available at 96KHz for a full 500ms. These all contribute to the satisfying response of Iridium.
Effector
Iridium models three tube amps; how did you analyze the amplifiers? When you compare the clean/overdrive sound created by tube amps and other amplified elements (like op amps, FET, JFET, MOSFET etc.), what would you say is the difference?
GS
The differences are contained partly in the shape of the nonlinear gain curves, and also in the transient response to overloading. The supporting circuitry used to create bias values also comes into play.
Effector
I assume that Iridium is mounted with a preamp with a JFET element; how does this contribute to reproducing the tube amp sound?
GS
The gain and frequency response of the preamp is accounted for in the first stage of the amplifier being modeled. It has some soft clipping at high levels that reacts in a very natural and tube-like way when hit with hot signals or gain/boost pedals before it.
Effector
Can you elaborate on ‘Matrix Modeling’?
GS
When recreating the response of linear circuit sections, the set of equations that represent the current and voltage of each element can be described by linear algebra techniques involving matrix math. Each element increases the size of the matrix, so it can get pretty complicated. But by solving the matrix you will get the exact response of the circuit described.
Effector
I suppose “Matrix Modeling” contains a huge amount of elements in its algorithm, as it says “From the unique composition of each tone stack, to component values, bias levels, corner frequencies, and tube stage gain”. Does ‘component values’ mean that you are reproducing the characteristics of every electronic device contained in one amplifier circuit?
GS
The component values determine the operating points and frequency dependent gain curves of the various tube stages, as well as the unique response of the tone stack circuits. Those are being accounted for in our process.
Effector
In ’Matrix Modeling’, how do you parameter the character of tubes contained in preamps, tremolo sections and phase inverters?
GS
We use a proprietary process to capture the parameters of the various tubes in different sections of the circuit. We feel it captures the extended range dynamic audio response of the tube sections. We do not currently have an amplifier model with a tube tremolo.
Effector
Suppose ’Matrix Modeling’ contains the effect of a power amp circuit on the output in its algorithm; could you tell what kind of sound it might create with each of the following tube constitutions; a.) 6V6×2, b.) EL84×4, c.) EL34×4?
GS
The difference in transconductance and clipping characteristics among the various power tube types results in more subtle sonic differences than the amplifier topologies and component values.
Effector
What does ‘Multi-stage power sag’ mean?
GS
In a tube amp, the B+ voltage is sent to the stages from the power supply through a cascading series of filtering sections, with each filter output feeding the previous tube stage. This causes interdependent sag characteristics at the supply rails for each tube section. This is accounted for in Iridium.
Effector
In ’Matrix Modeling’, do you take the effect from an output transformer into account on the overall sound?
GS
We include the effects of the output transformer and its interaction with speaker impedance in the amplifier model processing.
Effector
Also in ‘Matrix Modelling’, do you take the effect from power supply (transformers, diode etc.) into account on the overall sound?
GS
Yes, the transient response of the power supply is taken into account. It is one of the elements responsible for the natural feel and dynamics of the amplifier models.
Effector
In ’Matrix Modeling’, you are even taking the influence of speakers into consideration like ”compression, limited cone movement and distortion”. What measures did you take to parameterize such physical motions?
GS
We looked at the underlying electro-mechanical principles of the speakers and created a mathematical process to represent the various elements. This was then compared against real-world listening tests to verify.
Effector
Please elaborate on why you chose these particular three reference amps i.e. Fender Deluxe Reverb, Vox AC30 and Marshall Super Lead 1959 to model with Iridium.
GS
We chose those amplifiers because they represent the three most iconic and beloved amplifiers in the history of guitar amplification. They can span a wide variety of musical tones and styles, and they are just fun to play.
Effector
When you design to refer to these three amp models I suspect you listened to countless real amps from different periods and analyzed them with various pieces of equipment; can you give examples which units you actually tried?
GS
We had several examples of each of these amps and they all sounded good. We didn't try to obsess over finding the 'golden example', because that is a process that could have no end. We wanted to capture the familiar response and great tone of these amps as they exist all over the world.
Effector
I noted that Fender Deluxe Reverb, Vox AC30 and Marshall Super Lead 1959 are all different in the way they compose tone control. What did you have to consider when you divided them into Bass, Middle and Treble on “Iridium”?
GS
Our Matrix Modeling process made it easy to implement these different circuits. The hard part was developing the Matrix Modeling! But once developed, we could create and accurately reproduce the exact response of these tone circuits.
Effector
The tone control of old Vox AC30’s Treble, Bass, Cut has a unique feel when you play it, but is that particular feel reflected in the Iridium algorithm?
GS
Our Matrix Modeling captures the response and feel of those controls with exacting precision. The Vox tone stack is a unique circuit with a unique sound and we felt it was important to reproduce exactly.
Effector
“Round Amp”, “Chime Amp” and “Punch Amp” each have a distinctive character, but they’re very easy to control, and all sound consistently pleasant, no matter which output you choose - whether it’s mixer or guitar amp (from tube to solid-state, distorted or clean). How did you achieve such quality? What technological background and tuning made this possible?
GS
Iridium was developed over years of research and with the development of proprietary techniques to capture the qualities of these amplifiers. A robust platform was developed which allowed final tuning to our highest standards of sound quality.
Effector
Iridium responds very quickly with dynamics to whatever musical instrument you use; the pickup selector on guitars; the position of volume/tone knobs; the picking strength of players and vibrato: What kind of tuning made this possible?
GS
It is the sum of all the aspects of Iridium's signal flow and processing techniques that allow it to react naturally and dynamically to any input it receives.
Effector
How did you record the Impulse Response on the IR cabinet? If it was recorded in a recording studio with amps and microphones, could you tell us more about the spec of the recording room/booth and the recording equipment?
GS
The Impulse responses were provided to us by third party IR vendors specifically for the Iridium project. Our website has detailed information for the included IRs.
Effector
Could you please explain what the “Hybrid Room Reverb” is?
GS
The first 256ms of the Room Reverbs in Iridium are stereo impulse recordings of natural spaces (small, medium and large). These impulse responses create detailed spacial cues that place you in a realistic three-dimensional physical space. To achieve natural decay, we blend the room impulse responses with our algorithmic reverb decay.
Effector
All in all, Iridium is impressive in any making music situation, but as a developer, in what conditions would you say it could deliver it’s best performance?
GS
I have a variety of guitars with all different kinds of pickups and I just dial in Iridium to whatever suits me at the time. I can always quickly find a sound that I really enjoy playing with. That's the success of the project – to be able to just plug in, play, have fun and sound great!
Effector
As I was trying Iridium I could feel Strymon’s tremendous love and understanding for the tube amp sound, as well as exquisite taste and sensitivity in constructing the digital algorithms; What do you think is needed these days, as a brand, to create effect pedals which have enough musicality to capture players’ hearts?
GS
Thank you for the kind sentiment. Iridium was created from years of dedication, hard work, and some discoveries along the way. The goal was to produce something immediately familiar and fun, with the highest possible sound quality and musicality we could achieve. We try to keep these same principles in mind with each product we design.
Effector
With Iridium putting “Round Amp”, “Chime Amp” and “Punch Amp” to the market, the players who tried it may end up hoping that you would reproduce their own favorite old amps. I myself am actually looking forward to seeing amps like Supro and Ampeg revived by Strymon one of these days. Do you have any plans to make it into a series?
GS
We are encouraged by the excitement Iridium has generated. We'll see what unfolds in the future.
Effector
Do you have any messages to players who are considering Iridium?
GS
I encourage anyone who's thinking about Iridium to try one out. It really is a lot of fun and very rewarding to play through. And thanks for your support!
Effector
Thank you very much for your time and kind cooperation, as always!
