Introduction to distortion types

Why do foreign professional musicians basically use the distortion that comes with speakers? Why don't manufacturers just make the distortion that comes with the speakers into a separate effect? Why are tube speakers much louder than solid-state circuit speakers of the same wattage? If you already know the answers to these questions, then there is no need to read the following content.

1． What is distortion

Broadly speaking, when the output signal has a different shape from the input signal, it is distorted. But the distortion we often talk about as a guitar effect in music mainly means the following: First of all, it must be clear that any periodic signal can be decomposed into a series of superpositions of sine waves of different frequencies, so for the sake of simplicity, below Unless otherwise stated, we only discuss sine waves of a single frequency. At this time, if the output signal is supposed to be a sine wave, but its amplitude is limited by some device and mechanism, so that its originally smooth arc-shaped peaks and troughs are cut into a platform, then the kind of wave we hear will be formed. distortion. The shapes of the platforms of the waves clipped by different devices and mechanisms are not exactly the same, so there are different types of distortion we hear.

2． The Origin of Distortion

The earliest distortion comes from post-amplification. A complete electric guitar amplification system includes: (electric guitar ->) pre-amplifier -> post-amplifier -> speaker. In the 1960s, when rock music was in its infancy, all preamplifiers and preamplifiers were tube-based. At that time, the main function of the preamp was just to modify the sound to a certain extent, and there was basically no distortion. As rock musicians continued to ask for louder volumes (proportional to the square of the amplitude of the sine wave) in the latter stage, one day, the peak value of the output sine wave exceeded the maximum range allowed by the original design of the rear stage circuit, so the peak/ The troughs are forced to be flattened, and distortion is born! This kind of post-stage distortion caused purely by excessive volume is often called natural distortion. The Rolling Stones' sound is an early example of this kind of distortion. Many classic speakers that have been passed down to this day, such as Fender Tweed, Deluxe Reverb, Vox AC30, Marshall Plexi, etc., have this kind of distortion. Therefore, it is not difficult to understand why their distortion is not large. Because if the volume is too high, the speakers will either burn out or shock people to death. Almost all modern pure tube speakers (such as Marshall JCM800/900/2000, Mesa/Boogie Rectifier) ??even if the pre-amplifier has distortion, still uses post-amplifier distortion to a large extent. So the higher the volume, the greater the distortion.

3． Booster and preamp distortion

In addition to increasing the volume of the poststage, obviously if you increase the volume of the signal from the preamp to the poststage, it will also cause distortion of the poststage. Richie Blackmore and his peers began to think of connecting the guitar to the microphone interface of the tube recorder, and then connecting its audio output port to the guitar amplifier, so that the microphone amplifier circuit of the recorder could be used to boost the volume of the guitar. ). One such device was the prototype of what is now known as Volume Booster. Many stompbox effects appeared later, such as Ibanez Tube Screamer, Proco Rat, MXR Microamp, and DOD 250, all of which are Booster's masterpieces. Therefore, if they are used in ordinary speakers without vacuum tubes, their distortion performance is actually mediocre. Only by reducing the distortion on them, increasing the volume, and connecting them to a tube box can their charm be truly revealed.

But Booster cannot change the basic taste of distortion, and the improvement in distortion is not very huge. People soon noticed that if some parameters in the Booster circuit were changed so that its output signal also undergoes peak and trough distortion, it would be easy to obtain an effect with much greater distortion and a different flavor from the distortion of the subsequent stage. This is preamp distortion. From this, the emergence of metal music became possible with equipment. But after all, the flavors of pre-distortion and post-distortion are different. The output of the rear stage is a strong signal of up to 15-100W or even higher, which can only be used to push the speaker directly. It cannot be plugged into the front stage of another speaker as an input signal without adding bulky and complicated attenuation equipment. Therefore, all current stompbox distortion effects and the vast majority of rack-mounted effects (except rack-mounted speaker heads, because they are essentially power amplifiers that combine front and rear stages) are only front-end distortion, and the timbre of course cannot replace the front and rear stages. A complete set of pure tube speaker systems with distortion at all levels.

Usually when we talk about pure tube speakers, we mean speakers that use tubes for amplification in both the front and rear stages. There are some speakers now, such as the 65W or above products in the MARSHALL VALVESTATE series, MODE FOUR, LANEY's TF series, etc., but they only have electronic tubes in the front stage, but not a single tube in the rear stage, so they only have front-end distortion, which is different from pure tube boxes. There is still a big difference in timbre. This is because speakers with purely solid-state circuits at the rear stage basically have no distortion at the rear stage.

The root cause is that these circuits and their devices are originally designed for signal amplification without distortion. Once a circuit operates in a distorted state, the device is often on the verge of burning out. The output power marked on a speaker, according to industry practice, refers to the maximum power that the speaker can achieve when the output signal is undistorted. For tube speakers, they are usually designed so that the power amplifier begins to distort when the volume is turned up to about half. After that, if the volume continues to be turned up, the speaker can still work. And for rock guitarists, this is when the sound starts to sound good. But for pure solid-state circuit speakers, it obviously must be designed so that the volume is turned up to the end without burning itself out. Not burning out means that the rear stage has no distortion, so the pure solid-state circuit speaker only reaches its marked power when the volume is turned to the end. Now it is not difficult for us to understand why the tube speakers are basically as loud as the pure solid-state circuit speakers with the same power when the volume is turned to the middle.

4． Tube distortion and solid-state circuit distortion

Although distortion simply means flattening the peaks/troughs of a sine wave, because the specific circuit does not always work ideally according to the simplified theoretical model, the real wave pattern The cutting is always not so authentic. The work inside the electron tube must be realized by electrons flying back and forth between the electrodes. No matter how fast the electrons fly, it still takes time to fly in such a thick tube. Therefore, the response of the electronic tube to the input signal is always relatively slow, appearing a bit delayed, and the changes are not too drastic. It is reflected in the waveform, that is, at the connection between the original sine wave and the cut-out platform, the changes are always relatively smooth. The ear's reaction to this is a soft, warm tone. The solid-state circuit will cut the waveform very angularly, so it sounds more dynamic and the sound head is clearer, but after listening for a long time, it will feel harsh and thin.

Although the world's current mainstream understanding of sound quality is that tube distortion is comfortable to listen to, in a true pure tube circuit, the tube needs to work at a high voltage of several hundred volts. So only bulky rack-mounted preamps (such as tube preamps from ADA, Mesa/Boogie, Engl, etc.) can achieve tube distortion, while monoblocks driven by batteries or 9V transformers can only rely on solid-state electronics (usually diodes) Come clipping. As for some famous speaker simulators (Sansamp GT-2, rack-mounted PSA-1, etc.) headed by Tech21, they use solid-state circuits to simulate the signal response curve of vacuum tubes. Therefore, its sound head can still be softer and rounder than traditional solid-state circuit distortion to a certain extent. But after all, the existing technology is far from enough to distinguish the fake from the real one.

In recent years, a new technology has gradually emerged, which uses solid-state circuits to generate distortion, but uses electron tubes operating at low voltages to compensate. This kind of product can operate at a low voltage of 9-15V or even powered by batteries, and it has as much distortion as a solid-state circuit and does have a certain degree of pipe smell. From the many rack-mounted preamps with tubes in Rocktron's early years to the current Silver Dragon pedals, Ibanez's Tube King series, Guyatone's Flip series, and Vox's Cooltron series, they all fall into this category. Another big advantage is that the tubes running at low voltage will not be as short-lived as the tubes in real tube distortion. It’s amazing if the tubes under high pressure can last for a year or two, but the tubes in these effects can even last a lifetime. And just like a pure tube speaker that needs to be "burned in" for about half an hour to get a good tone, the sound of these effects units is also "burned in" the better, but their "burning" time is also like their lifespan, which is amplified to several Measured in years. Based on these advantages, some manufacturers have also launched products that use preamp tubes to compensate solid-state power circuits, such as ADA's MICROTUBE power amplifier and VOX's VALVETRONIC series speakers. Of course, the final quality of a signal depends on the weakest link in the circuit. As long as the distortion is still caused by solid-state devices, no matter how much the tubes try to compensate, they still cannot fully compensate for it.

5. Digital Distortion

The emergence of digital technology allows us to cut sine waves into any desired shape in principle. But why do people still generally think that the result of digital distortion imitating tube distortion is not as good as ordinary solid-state analog (the "analog" here corresponds to the English ANALOG, which is relative to "digital" and does not mean "imitation"). What about circuit distortion? ? At this point we have to review the wave decomposition mentioned at the beginning of this article. Since any periodic signal can be decomposed into a series of superpositions of sine waves of different frequencies, the above discussion only discusses the distortion of sine waves of a single frequency for the convenience of illustrating the problem. But in fact, the sound we finally hear can only be the total effect of waves of various frequencies synthesized together. For tubes and solid-state analog circuits, this decomposition and synthesis is only mathematical and has no substantive consequences. But digital circuits have an eternal limit, which is that they cannot handle continuous things. Sound waves are originally continuous (so they are called analog signals), but digital circuits must first cut them into pieces, convert them into numbers (this process is often called analog-to-digital conversion), perform operations, and then synthesize them in turn. A whole (digital-to-analog conversion) is broadcast. Obviously, the more slices per second, the closer it is to the true continuous distribution of the original signal, which is what the "sampling rate" describes.

But no matter how digital technology develops, as long as it is digital, the sampling rate must be a limited value. Reflected in the decomposition of waves, it is equivalent to retaining only certain components of certain frequencies in the input signal, rather than all frequencies. In this way, even if the sine wave of each component is cut into a platform according to the shape of an analog circuit or a tube circuit, when it is finally superimposed into an output signal, due to the lack of some frequency components, the synthesized result is equivalent to the platform There are a lot of "burrs" that rise and fall rapidly at the beginning and end. What's more, when clipping, digital circuits can only mechanically convert the amplitude of the wave into discretely distributed numbers for processing. As a result, the synthesized "burrs" are even more serious. Therefore, when we listen to it in our ears, over time we will naturally have a scratchy and irritating feeling.

But thankfully, whether a distorted tone sounds pleasant or not mainly depends on the device that produces the distortion, and whether it has been processed by a digital circuit is not too important. Therefore, although digital delay or other peripheral effects do not completely have no negative impact on the sound, as long as the distortion is not digital, it generally does not sound too uncomfortable. Therefore, for a current professional guitar amplification system, the front and rear stages usually use pure tubes, plus tube reverberation. It is best to have tube compensation at both ends of the effect loop.

As for whether the delay and other weird effects in the middle of the loop are digital, you can just turn a blind eye