The nature of the sound of tube amplifiers
Exciter (from the English Exciter), also called harmonic exciter (harmonic exciter), psychoacoustic processor (psychoacoustic processor), enhancer (enhancer) and acoustic exciter (aural exciter) – this is a processing device used for the harmonious synthesis of high-frequency signals, using thin harmonic distortion.
This harmonic synthesis consists in creating higher harmonics based on lower signal frequencies. Typically, noise is present in different frequency bands in unequal amounts, and harmonics obtained from a clean frequency band will be clearer. Less commonly, exciters (enhancers) are used to synthesize low-frequency harmonics in order to simulate deep bass.
Initially, exciters were made on the basis of tube amplifiers, but now they exist in the form of digital processors.
Exciters and enhancers are used to change the tonal qualities of sound. But, unlike the equalizer, which simply enhances or attenuates the frequency present in the signal, enhancers can create new harmonics.
Equalizer does not add additional harmonics to the sound. It is used to amplify or attenuate an existing frequency. An equalizer is used to emphasize the characteristic overtones of musical instruments and amplifies a specific frequency domain. In the case when the required frequencies are initially small, the equalization will not give the desired effect, or together with a weak signal it will remove all unwanted noises.
Fine processing by an exciter, with its competent use, gives a feeling of transparency and increased intelligibility of the sound. Although a misunderstanding of the process of excitating can lead to rather disastrous results. For example, an exciter does not make sense to process an organ or brass instruments, which are characterized by a ruled spectrum of fundamental tones. Exciting an instrument, which by its nature does not have overtones, can cause a very unexpected and most often unpleasant effect.
Unlike traditional equalizers, using an exciter is less likely to add noise and hiss that make the sound less clear, especially for tape recordings of analog tape that have lost their “sparkle” due to frequent overlays.
– Exciters are also used to restore old records, adding lost spectral composition.
– Exciters are sold as pedal effects specifically designed for electric guitars, basses, or electronic keyboards.
– Exciters are very often used in mastering.
Unlike the equalizer, the exciter itself completes the higher harmonics, starting from the envelopes of the fundamental tones. That is, there is no amplification of the required frequencies, but a logical addition of new overtones (harmonics).
Exciters, as a rule, create harmonics that are multiples of 2, (2, 4, 8 …), which, according to auditory sensations, gives clarity and greater intelligibility to the sound, “volume” and “warmth”. Despite the fact that the overall volume remains the same. Unlike harmonizers, which, as a rule, create harmonics in the entire band of the audio signal, exciters make it possible to choose the frequency of enrichment.
But exciters also have an inverse negative property: when listening for a long time, the listener wants to constantly increase the saturation of sound with harmonics, so after some time when listening to sound without an exciter, a recording made with his participation may seem like an oversaturated “mess”.
Now let us turn our attention to tube amplifiers, which so often are presented to us almost as the only devices capable of qualitatively amplifying sound vibrations and transmitting all the bulk, warmth and many other attributed properties.
At present, tube amplifiers are an object of commerce and speculation precisely because the nature of amplification of sound vibrations is based on the excitation mechanism (but usually sellers don’t like to focus on this, because, thanks to this effect, it’s possible to attract buyers of expensive equipment )
As you know, the auditory perception of sound is a subjective thing. The human ear accurately identifies a sound saturated with harmonics as closer or louder when compared to the same sound without harmonics. For example, the sound of a guitar string or piano during a strong beat is much more enriched in harmonics compared to soft sound extraction, but still the listener will easily identify a strong beat as louder and closer, even if the amplitude of the second is slightly larger than the first. As you know, most tube amplifiers have a harmonic coefficient of about 1%, which gives the effect of “approaching” (exciting) the background (it should be noted, this is in the case of small intermodulation distortions, which is typical for tube amplifiers).
For this reason, a revision of generally accepted views on the “phenomenal” quality, “detail” of the sound and the indispensability of tube amplifiers is necessary.