Technology

Another popular form of meter is the LED chain. Unfortunately it has a disadvantage, too: When the standard driver units are used, the change between two values always happens abruptly. A single LED in the chain can therefore only show an imprecise value in a defined interval. Hectic flicker indicates that the actual value must be somewhere in between.

elysia solves these problems by introducing the analog dynamic display that combines the benefits of both VU meters and LED chains. This meter is based on LEDs, too, but a special circuit design makes it possible to show interim values by modulating the brightness of the LEDs. This means a true analog way of showing the operation of the compressor: It is very fast, but with smooth transitions. The user gets an important tool for precise gain reduction monitoring – finally the relationship between acoustic and visual perception feels just right.

For this reason, you can switch the release curve of the mpressor from linear to antilogarithmic. The Anti Log curve behaves just the other way round: When the threshold value is passed and compression sets in, the release time stays longer as a start. When the input signal starts to decline, however, the release time will become faster as a result.

A special circuitry makes this behavior independent from the absolute amount of gain reduction. No matter if the compressor reduces 10, 15 or 20 dB, the curve will always stay the same at the start and will only become faster at the end. Consequently, many exceptional compression effects can be created just by the push of a button.

The special problem with bass is that in case that the B string is played it produces frequencies as low as 30 Hz, which is equivalent to a period of 33 ms between the waves. The result is that a fast attack setting will have its effect on every wave anew, producing unwanted artifacts.

Longer attack settings reduce distortions significantly, but now the compressor is too slow on fast impulses. The intended compression now turns into an expansion, because the fast and loud impulse is not processed, while the level of the sustaining signal will be reduced. A slap-style bass displays this phenomenon very well.

This is where elysia’s Auto Fast function comes into play. If you set the attack to 80 ms and then engage the Auto Fast mode, the attack time will automatically be shortened on fast and loud signal impulses (e.g. string hits fingerboard when slapping). The compressor quickly reduces the signal and prevents it from 'slipping through'. Afterwards the attack time directly and automatically returns to its original setting. In Auto Fast mode the compressor can be very fast, but only when it is really needed!

This function influences the attack parameter on short and loud impulses only, in all other cases the original settings of the controller stays valid.

The idea behind this is to reduce the amplification of high frequencies. Sometimes further external capacitors are added into the negative feedback path to achieve this. The problem with it is that these capacities have a negative effect on the sound quality of the signals that pass these stages.

The corollary was to design a circuit working without capacitors that would affect the frequency spectrum. Intensive research finally led to a concept that has all the advantages but none of the downsides of a classic op-amp: the current feedback amplifier. The current is directly modulated by the negative feedback and therefore avoids the time delay in the differential amplifier. The overall signal delay is clearly shorter and the phasing will stay intact even in high frequency areas.

Featuring an enormous slew rate and true reproduction of impulses, the amplifier can handle frequencies up to several MHz. The enjoyable results are clean high frequencies, a very good projection of details and open as well as natural dynamics. Certain parts of the circuitry feature additional special capacitors which influence the frequency response selectively in fine nuances in order to even further round out the sound experience.

In addition, this amplifier can be tuned to work at a very low harmonic distortion level or also add a pleasant amount of K2 if wanted. Therefore some of the amplifier stages in the mpressor have experienced further fine tuning depending on their particular purpose. The resulting sonic quality is beyond any doubt and shows that classic analog design is still state-of-the-art for audio processing on the highest level.

Further on we have placed additional MKP capacitors into many parts of the circuits in order to provide the current needed locally in a very fast manner. The voltage for the electronics is precisely kept at +/-30 volts. The voltage regulation is built with discrete circuits, keeping the noise of the power supply so low that one can hardly measure it at all.

The measured hum is cancelled much better than standard voltage regulators are capable of. This is an important condition for clean and clear sound results. If there were higher amounts of noise and hum in the voltage supply, the amplifier stages would have to compensate for that and would not fulfill their actual duty as well as intended.

The diode rectifiers have their influence on sound, too, because they have to recharge the electrolytic capacitors for a short moment and have to provide current for all circuits while doing so. Therefore elysia uses very fast and acoustically tested diodes for that purpose.

If now the fader was limited by a piece of duct tape at let’s say 10 dB, it could only reduce the signal up to this value. If the input signal got even louder, the fader could not be moved further down because of the duct tape limit, and the output signal would again start to become louder corresponding to the input signal.

Because of this, loud parts in an arrangement can keep their dynamics, as they will not be compressed anymore once their level goes beyond the threshold of the Gain Reduction Limiter. Some very nice special effects like ducking or true upward compression can be achieved with it easily by just reducing the lower signal without changing the original dynamics at the same time.

The filter used for this application is an all-pass variant with flat frequency response that changes its phasing correspondent to the setting of the frequency controller. When the signal that went through the all-pass is afterwards mixed to the original again, signals that are in phase will be amplified and out-of-phase signals will be reduced.

This is how the special frequency response of the filter comes off. Because the filter signal is mixed to the original, the genuine structure and impulse-response can be contained to a large extent. None of the amplifiers will be shortened in their frequency response, which results in an open and dynamic sound. By simultaneously boosting and cutting the selected frequency-areas, it is much easier to influence the character of a track ('bright' vs. 'dark') compared to using other types of equalizers.

To ensure that an amplifier is operating in constant class-A mode, no matter what its actual input is, the quiescent current must not be set too low. One of the great advantages of discrete circuits is that the developer can decide what this value should be. elysia sets the quiescent current at 14 mA which is an unusual high value for audio circuits.

Doing so, the transistors will always be conductive, even when there are small resistor loads and high amounts of current. Crossover distortions cannot occur. For comparison: The total current consumption of a typical audio op-amp NE5534 is 4 mA and the quiescent current about 2 mA. The measurable crossover distortions of these op-amps are very small, too. However, this can only be realized by high amounts of feedback that need more signal stages, having negative effects on the fidelity of the signal in turn.

To guarantee pure class-A mode, elysia utilizes power transistors normally used in power amps in the output stage. The sonic result is a clear increase of immediacy and dimension – all signals sound more present and massive. With a value of 2W each, the emitter resistors are also over-dimensioned in order to improve the projection of details even further.

With the T12 Heater elysia presents a system that arranges constant conditions and reduces the thermal fluctuation to a minimum. This system was inspired by high-precision measuring instruments. It features up to 12 discrete transistors in a massive copper ring that is warmed up to a definite temperature.

Once the system has reached its working temperature, it only needs little current to keep it at the same level. An electronic control circuit is responsible for a small variance of only a few degrees. The procedure is known from high end tube gear: the mpressor should be granted an adequate warm-up-time in order to experience it absolute top form.

The benefits of discrete electronics design can once again show their strengths by tailoring the sound via the concept of the circuitry and the choice of components. A countless number of different circuitry variations were built, tested and listened to during the development process of the mpressor in order to finally achieve the optimum result.

The discrete transistors of this specific module are integrated into a copper ring where they are purposeful heated up in order to make them insensitive towards external, temperature-related influences. A further advantage of the TCA topology is the very fast response to the control voltage. This is the basis for a compressor that can even handle rapid changes in dynamics and extremely fast time constants.

Further on remarkable is the fact that the make up gain was designed as an amplification of the input signal. This is running parallel to the sidechain path and therefore does not have any unwanted influence on the control behavior. The essential advantage of this arrangement is that the background noise always stays at the same low level, no matter how much amplification is applied.