Previously, in March 2022, we wrote an article on the Stomp-box Modeler comparison, introducing common products on the market, such as NUX Amp Academy, Strymon Iridium, Walrus ACS1, Atomic Ampli-Firebox, BOSS IR-200, etc.
而主打Plug-In軟體的IK Multimedia也在AmpliTube的基礎上，推出Stomp-box Modeler: TONE X。 TONE X採用的算法是類似QC的AI建模，源自跟KEMPER系出同門的『黑盒算法』。
IK Multimedia, which mainly focuses on Plug-In software, also launched the Stomp-box Modeler: TONE X on the basis of AmpliTube. The algorithm adopted by TONE X is an AI modeling similar to QC, which is derived from the "Black Box Algorithm" of the same family as KEMPER.
Before explaining Modeler and Profiler, let's talk about the difference between Amp Modeling and IR. I found that many people are confused about the definition of the two.
The "Amp Simulation" we mentioned in Mandarin refers to "Amp Modeling", which is the action of modeling for an "Amplifier". We will talk about the Modeling method later.
(由上圖可知IR所還原的就是『麥克風收取箱體（喇叭）』的聲音。
From the picture above, it can be seen that what IR restores are the sound of "Micing the Cabinet (speaker)".)
IR is actually a method used to realize Cab Sim in recent years. As mentioned in the previous article, in recent years, due to the increase in DSP computing power, the early method of using filters to do Cab Sim has been replaced by IR convolution. So IR refers to "Cabinet Simulation", not "Amp Simulation".
Amp Modeling: Modeler & Profiler
音箱模擬，顧名思義就是要去『模擬』音箱，那麼我們得先來看一下，我們要去模擬什麼樣的音箱。
Amp Simulation, as the name suggests, is to "simulate" amplifiers, so we have to take a look at what kind of amps we want to simulate.
First of all, we understand that the object we want to simulate, "Electric Guitar Amps", has a very important characteristic, that is, it has a "distortion" signal. Even what we think of as a cleanish category amp has distortion characteristics compared to an Acoustic Guitar Amp or PA system.
The main part of the electric guitar amplifier to form the tone is the PRE-AMP, which is also the source of the main distortion characteristics. Therefore, Digitech, Zoom, and Line 6, the three classic brands (main brands from 2005 to 2010), adopted the "Waveshaper" modeling method during the development of the semiconductor industry at that time. The advantage of this approach to modeling is that engineers don't have to understand how vacuum tube circuits work. (I was born in 1983. When I studied at university, the Smith Electronics textbook had no "vacuum tubes". At that time, the electronics industry was already dominated by semiconductors.)
這是Preamp的最後一級，旨在驅動效果環路，也是第一個出現失真的Preamp級。 該設計類似於 Mesa Boogie MK I 中的Preamp失真級。
This is the final stage of a preamp designed to drive an effects loop and is the first preamp stage to break into distortion. The design is similar to the preamp distortion stage in the Mesa Boogie MK I.
The cathode resistor is fully bypassed to prevent negative feedback from reducing the triode circuit's lush nonlinear behavior. R1 and R2 form a voltage divider to reduce a maximum plate voltage swing of about 100V peak to a maximum effect send swing of about half a volt peak.
According to the 12AX7 Calculator, the grid is biased at a very warm -1V.
As the input signal level increases, positive grid voltage swings are compressed by the effects of grid current on the upstream resistor network. Negative swings of the input signal run free. The severe asymmetry produces bucketloads of 2nd-harmonic distortion that plateaus early and lasts until negative grid voltage swings reach approximately -3V. At that point, the peak-to-peak plate voltage swing has almost reached its limits.
When negative grid voltage swings exceed -3.5V, positive plate voltage swings transition from mild compression to sharp clipping. The output waveform becomes more symmetrical and 3rd-harmonic distortion begins to dominate. Beyond that point the output signal is at its maximum - it cannot respond to further increases in input signal amplitude.
Traditional Waveshapers (Waveshaper Modeler)
傳統上，電吉他音箱的非線性行為是通過『Waveshaper』來建模的，它將輸出描述為輸入的函數。 例如，這是 Line 6 專利中包含的『波形整形器』（Waveshaper)。
Electric guitar amp nonlinear behavior has traditionally been modeled by a 『Waveshaper』, which describes the output as a function of the input. Here, for example, is a waveshaper included in a Line 6 patent.
對於線性電路，傳遞函數是一條直線。 Line 6 Waveshaper在正負輸入擺幅的極端情況下顯示壓縮。 它還描繪了不對稱失真，因為正電壓擺幅的曲線不是負擺幅曲線的鏡像。
For a linear circuit, the transfer function is a straight line. The Line 6 Waveshaper shows compression at the extremes of positive and negative input swings. It also depicts asymmetric distortion, because the curve for positive voltage swings is not the mirror image of the curve for negative swings.
以及 “Cubic Spline Interpolation of the Transfer Function“、” A Digital High-Pass Filter to Emulate the Coupling Capacitor“ 等作法。
It is estimated that non-engineering friends have fainted, so let's stop here. Regarding Waveshaper modeling, there were more improvement methods in the later stage, such as " A high-pass filter that captures the low-frequency behavior of coupling capacitor CG".
And “Cubic Spline Interpolation of the Transfer Function“, ”A Digital High-Pass Filter to Emulate the Coupling Capacitor“, …etc.
Specific knowledge of the application's code, internal structure, and programming knowledge. In general, is not required. The tester is aware of what the software is supposed to do but is not aware of how it does it. For instance, the tester is aware that a particular input returns a certain, invariable output but is not aware of how the software produces the output in the first place.
The black-box algorithm is to guess the working status of the whole machine by virtue of the signal input/output relationship without knowing the internal structure of the physical amplifier or effector. When the correct rate of guessing reaches a certain level (for example, higher than 98%) That is to say, the sound of this amplifier is realized.
The advantage of the black-box algorithm is that it has a simple structure and does not require high computing power. Generally speaking, the black-box algorithm uses a simple general-purpose structure to realize the simulation of sound. Under the same computing power, black-box algorithms can usually obtain good accuracy. His main shortcoming is that it cannot cope with the real-time change of tone when the internal mechanism of the system changes. For example, amplifiers and effectors have adjustment knobs such as volume, high, mid, bass, gain, ...etc. When profiling a model with the black-box algorithm, the above knobs need to be fixed at one position, and then the input and output characteristics of the signal are tested to obtain the parameters of the model. Once the position of the knob is changed, the relationship of the model to the new system does not hold. Therefore, this method is suitable as a method of taking pictures, and the sound of the current amplifier is fixed to use.
The white-box algorithm is to open the shell of a device to see what components are used inside and how the components are connected and then uses a set of mathematical equations to realize the working state of the entire machine.
White-box testing's basic procedures require the tester to have an in-depth knowledge of the source code being tested. The programmer must have a deep understanding of the application to know what kinds of test cases to create so that every visible path is exercised for testing. Once the source code is understood then it can be analyzed for test cases to be created.
When choosing to build a virtual device, you must first determine what physical system to use as the basic conditional constraint. For electronic networks, you only need to follow Newton's law and Kirchhoff's voltage and current laws:
The above laws can satisfy the expression of the general resistance-capacitance circuit network. If it is necessary to introduce magnetic field components such as transformers and inductance coils, Faraday’s electromagnetic law can also be introduced:
Arbitrarily complex circuit topologies can be described through the above four laws. Since this way of expressing the system does not involve any artificial influence, a very natural signal response can be obtained, which is the charm of the white box algorithm.
Below we use two examples to explain how to solve the above system. The figure below is a classic circuit for mic preamp mid-EQ. The circuit includes three linear components: resistors, capacitors, and inductors:
I know it's hard to go on here, let's just talk about the characteristics of the white-box algorithm.
The advantage of the white-box algorithm is that it can completely reflect all the characteristics of the simulated equipment, including the adjustment knob of the equipment, the influence of parameters such as power supply and temperature on the sound, etc. It also achieves the same dynamic response (what players call playability) and highly realistic tone as simulated equipment.
The main disadvantages are:
1. It is necessary to establish a separate mathematical model for each analog device, such as tubes, transistors, operational amplifiers, resistors, capacitors, inductors, transformers, and other components, as well as how the circuits of the analog devices are connected, so the workload is huge.
2. It is necessary for the designer to have a very deep theoretical knowledge of analog and electrical design in order to reproduce the sound of the prototype.
3. A large amount of DSP computing power is required to achieve high accuracy of the model.
上面的圖片就是NUX品牌採用『白盒算法』建模的程式網路結構。
The picture above is the program mesh structure modeled by the NUX brand using the "white-box algorithm".
From the previous introduction, we can understand that Amp Modeler can be divided into Modeler and Profiler. Here we add a new approach, which is "AI neural network".
In 2020, Neural DSP released Quad Cortex, which uses the AI algorithm. The AI algorithm is an extension based on the "black-box algorithm". It also does not need to know the system content to measure the relationship between input and output signals. AI lies in the fact that testers are not required to test, but are tested independently, and trained according to the assumed system equations to obtain the equations that are closest to the reference output results.
而最近IK所推出的TONE X也是基於AI。（IK稱為MACHINE MODELING。）
The TONE X recently launched by IK is also based on AI. (IK named it MACHINE MODELING.)
To sum up the above, Amp Modeler is divided into Modeler and Profiler, and the technology of the Modeler is divided into Waveshaper and White-box. Profiler technology is divided into Black-box and AI.
The reason for using Waveshaper is that engineers do not need to have the knowledge background and working principle of the vacuum tube circuit mathematical model. The Amp Model mathematical model established is relatively simple and does not consume DSP computing power.
But the disadvantage is that it cannot restore the negative feedback and dynamic response of vacuum tube amplifiers, which will affect the playability. The most obvious thing is that when you connect an "Overdrive pedal" externally, the sound will be compressed and shrunk. It cannot withstand large signals like real tube amplifiers.
As mentioned earlier, the white-box algorithm tests that the engineer must have a high degree of knowledge background on the system (that is, the tube amplifier circuit), and the Programmer must also understand the mathematical model of the physical modeling of the system. In addition, the circuits at each level need to be measured and corrected, so the reference needs to be disassembled for verification, and the modeling process is quite time-consuming.
But for musicians, the most important thing is that White-box is the closest to the "playability feedback" and "overdrive signal tolerance" of tube amplifiers, as well as the "chaos phenomenon" when turning the EQ knob.
The modeling process is fast, so the brand or the third party can perform Profiling and share the Profile file often. (Amp Model)
But the disadvantage of Profile is the static parameters. When you turn the EQ, it will be different from the reference, and you will find that although the overall frequency response is similar to the reference, the playability is fixed, even if you change to different amp models. When you plug in an overdrive, the sound will be unnaturally compressed.
The modeling speed is the fastest, its built-in general model, AI self-training fitting curve equation, and the process of Profile is simpler than a traditional black box. The overall frequency response can be more accurate than the traditional profiler.
But the current AI profiling time is still quite long, for example, Neural QC takes about 40 minutes, and ordinary users still rarely use this function.
In addition, the same disadvantage as the black box algorithm: the playability is fixed, even if you change to a different Amp Model. When you plug in an overdrive, the sound will also be unnaturally compressed.
The chances of modern guitarists choosing Modeler are getting higher and higher because there are more and more Amp-less (no speaker) scenes during performances. Guitarists who like effect pedals will choose the Stomp-box Modeler type to match their favorite effectors, especially "Overdrive" and "Distortion".
所以，如果你的考量是以live gigs為主，那麼挑選『白盒算法』為基底的NUX Amp Academy 將會是一個好選擇。 如前所述，『白盒算法』擁有近似真空管音箱的『Negative Feedback』、『良好的彈奏手感反饋』、『優異的動態範圍』、『過載效果信號承受性』。
If your consideration is based on live gigs, then choosing NUX Amp Academy based on the "White-box Algorithm" will be a good choice. As mentioned above, the "White-box Algorithm" has "Negative Feedback" similar to vacuum tube amplifiers, "good playability feedback", "excellent dynamic range", and "overdrive signal tolerance".
In addition, the product itself has an XLR output and a 1/4” (6.35mm) output that can independently switch the IR on/off. With OTG, you can use your mobile phone for in-depth parameter adjustment. Send/Return is connected to an external post effector.
But the disadvantage is that there is no traditional MIDI port or 3.5mm MIDI port, if you want to use MIDI pedals, you need to use a MIDI controller with USB HOST.
If you mainly do home recording and hope to have more Amp Models or presets(patches) made by third parties, then Profiler will be your choice. Home recording has lower requirements on playability and it is a very common usage scenario to use DAW plug-in effects to modify the audio track after recording, so there is no need to consider the "overdrive signal tolerance". And the Profiler sounds more like a "processed sound". (Like the guitar sound recorded on a record.)
The most discussed affordable Profiler on the market recently is IK ToneX. In the editor's experience, the regrettable part is that the interface and logic of editing presets are very different from those of general multi-efx devices. The machine itself only has an LED screen, which displays little information, and the parameter adjustment is not friendly. In addition, there is no Send/Return to external post-efx. If you want to capture other references, you need to purchase ToneX Capture separately.
Note: If you have bought IK ToneX and are not familiar with editing tones, you can refer to this tutorial video.
Recall, what I call "Overdrive Signal Compatibility".
IK ToneX vs NUX Amp Academy | Twin Reverb
IK ToneX vs NUX Amp Academy | Super Reverb
IK ToneX vs NUX Amp Academy | JCM800
Neural Quad Cortex vs NUX Amp Academy
NUX Amp Academy vs LINE6 HX STOMP | Fender Twin Rvb & Friedman BE-100
Strymon Iridium VS NUX Amp Academy | Drive Pedal Headroom & Response Test
相信聽完以上的對比後，大家應該更理解我所謂的『彈奏手感 Playability』、『動態範圍 Dynamic Range』、『過載信號兼容性 Overdrive Signal Compatibility』。
青菜蘿蔔各有所好，愛其所擇，擇其所愛～ 錢沒有不見，只是變成你喜歡的樣子！
I believe that after listening to the above comparison, you should understand what I call "Playability", "Dynamic Range", and "Overdrive Signal Compatibility".
Vegetables and radishes have their own preferences, love what you choose, choose what you love ~ the money is not gone, it just becomes what you like!
結尾附上小彩蛋～ IK TONEX與NUX AMP ACADEMY個別的耗電量：
Amp Academy Firmware V4
(2024/04/04 更新blog)
最近NUX又更新了Amp Academy，我相信大家最關注的不外乎有哪些新的Amp Model?
讓我們來瞧瞧～
1. Fender Deluxe Reverb (Deluxe Rvb搭配 IR "FDR112 BLU")
2. VOX AC30 (Classic A30 搭配 IR “A30 212 BLEND”)
3. Fender Princeton (Princetone搭配 IR “JEN P10R")
4. Mesa Boogie Lonestar (LSTAR 搭配 IR ”MES 212 V30”)
