Modulare Serie

afis – artistic fidelity isolator switch

Digital reference monitoring matrix | Galvanic isolation – Filter – Reclocking

afis

The influence of interference voltage from digital electronics, computers and IT peripheral devices on the quality of music playback is usually massively underestimated. Because in addition to the direct influence on the analog signal which is generally possible, it should be especially noted that every form of interference in complex mechanisms via Jitter (clock instabilities) has an effect on the audio signal. So the issue of "avoidance of interference" is of central importance for the ideal, faithful playback of music.

Therefore, the first device of the arfi series, the afis, was conceived as a central switching unit to conduct signals of various digital formats from various sources as faithfully as possible to the DA converter. In addition to galvanic isolation, filtering and reclocking (regeneration of a new precise pulse synchronous to the incoming pulse), the device has a switching unit for four different input signals. The device can thus integrate various digital sources (CD players, audio interfaces, etc.) and the DA converter into the digital transmission route. The afis suppresses interference from any source and creates precise, clean pulses for the outgoing signal to the DA converter.

This last idea is not quite new, however the afis has a brand new approach: this type of interim switching device can only have an effect on the sound of the DA converter that follows. A super-precision oscillator in the reclocker is thus totally useless on its own. Only the actual effective clock precision in the DA converter is crucial. For this purpose, the issues of interference suppression, EMC and cable technology are far more important than the actual oscillator precision. For example, the XLR and cinch connectors became standard around 40 years ago because they were common in analog technology. However, they are only suited to digital signals to a very limited extent because the impedances do not really match and the wrong impedance can produce signal reflections on digital cables, thus producing inadequate signal quality. Faithful transmission is not possible without solving this problem. Therefore, reclocking is only one of the many features of afis. Blocking interfering signals and cable technology are far more crucial to actually transmit the precision thus generated to the DA converter. This increases the quality of the digital-analog conversion in the connected DA converter.

In professional use, you have a true assessment of the work, because external influencing factors are minimized. The sound contains more fundamental and is tonally more balanced. There are gains in precision and spatial resolution. The main thing is fine musical details that were previously masked will now be audible. For the music lover, a fully new listening experience where the artistic expression of the interpreters can be relived in an unheard intensity...or simply and tangibly more pleasure listening!

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afi+USB – artistic fidelity isolator + USB module

USB playback interface in a class of its own

afi

afi is based on the same technology as afis. Basically, the devices only differ in their equipment options for input and output modules. Whereas the afis can be equipped with four input modules of selectable formats and two different outputs, the afi is intended to be used with an USB module and has an output in RJ45-Ethercon format, which with the help of various connection options is optimal to hook up to a DAC. The afi+USB thus forms an extraordinary USB interface, the ultimate solution for digital playback from a computer.

USBmodules 600

arfi optical fWeb020518 3k6en 

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 go to USB-Modul 

 

 

USB audio converter module

The USB module transforms the afis or afi, in connection with a computer, into a full-fledged, very high-quality audio source device. The computer becomes a music player. The issues of "avoiding HF interference and clocking precision" are perfected here.

In principle, a computer is ideal for managing a digital music collection and playing back music with regard to its flexibility and operating convenience. Unfortunately from a sound point of view, a computer is the most inhospitable environment possible for an audiophile's enjoyment of music. Computer are machines that calculate at high clocking rates and run innumerable processes during music playback. As a result, they create a broad spectrum of high-frequency disruptions.

In order to keep this unavoidable interference from the computer away from the sound-sensitive audio section, the USB option has a two-part design:

1. The external USB-FOC module

for communication with the computer 

 

USBmodules 600

2. The internal USB module

built into afi or afis, which takes over all tasks of the music playback procedure which are relevant to the sound.

USB inputmodule

Both units are connected to each other with the help of three fibre optic cables (FOC) for maximum isolation from interference. Thanks to the optical coupling, there is no direct electrical pathway for HF interference from the computer to the audio section. Both units are completely galvanically isolated, mass flows are eliminated.

However, the most important difference between this and a conventional transmission of a digital audio signal via optical cable from the computer to a DA converter is the following: if a conventional digital signal is transmitted via toslink, then the clocking signal is embedded within it. The clocking information is at the same time the HF interference of the computer in the form of Jitter, and Jitter is very difficult to completely remove after the fact. Therefore, the optical audio connection does not eliminate the interference from the computer.

In contrast, the FOC connection of our USB module contains no clocking information that is relevant to the sound. Therefore there are a total of three FOCs. The external USB module receives the clocking information from an internal module. The reference oscillators sit in a perfect environment, fully decoupled from the computer, clocking the audio stream coming from the USB module in addition to the external unit. With regards to the clocking quality of the FOC connection itself, neither the clocking information going to the external USB module nor the audio stream from the external module have any influence on the audio quality. The double (duplex) FOC is responsible for both the clocking to the USB module and the audio from the USB module. The third FOC transmits the switching signal for each sampling rate family. Depending on whether the rate is 44.1 kHz multiples or 48 kHz multiples, the appropriate oscillator is activated.

AFI USB Modul Grafik1

The external USB-FOC module with a USB-B jack (1) to be connected to the computer, a duplex FOC connection (2) and FOC interconnection (3). Optionally, a separate 5-Volt power supply unit (1A) can be connected via the DC connector (8). With the sliding switch (7) you can switch between power supply via USB (Standard) and the DC connector. The RJ45-Ethercon output to afis or afi is either directly connected via RJ45-XLR cable (4) or via RJ45-RJ45 cable (5) plus adapter box (6) to the DAC.

USB module3 600

Further information:

Our sophisticated transmission concept in our USB module for Afis and Afi strives to keep this HF interference as separate from the audio signal processing as possible. There are several deciding factors here:

  1. USB is the most common interface today to connect audio devices with computers, at least in home audio. But USB is actually the worst interface imaginable for this, because USB cannot be galvanically isolated. Galvanic isolation is - often mistakenly assumed - not a cure-all for HF interference. But this is an important component to achieve interference suppression at all. But because this is not possible, all interference generated in the computer is to a large extent transmitted to the USB interface. Therefore, the small external USB module is far away from the audio electronics.  
  2. USB interfaces also work with a micro-controller and today such processors are sometimes enormously powerful, which again means a high potential for interference. This is also why the USB interface is placed in the external USB and thus far away from the audio electronics.
  3. The external USB module is connected with the actual Afi or Afis audio device via fibre optic cables. This connection guarantees perfect galvanic isolation, maximum interference suppression full immunity against disturbances and the connection is also guaranteed not to disturb itself. These FOC are available in 2m and 6m. It is thus simple to keep the computer with the external USB module separated from the audio electronics. Distance is the easiest way to protect against interference.
  4. The clocking, which is so crucial for DA conversion, is generated in the Afi or Afis itself under optimal conditions, free from interference factors from the computer and from the USB interface. The audio signal arriving from the USB interface via fibre optic cables are then reclocked on the basis of this precision clocking and is thus free of any disruptive influences coming from the computer. The fibre optic cable connection protects the system from interference and the clocking is created in the Afi or Afis. The digital signal, which is sent from the output of the Afi or Afis to the DAC, has optimum clocking quality and no longer contains HF interference coming from the computer or the USB interface that could disrupt the clocking reference in the DA converter during the conversion process or the analog stages directly.

In short: the essential feature of the Afi(s) + USB, which separates it from all other solutions, is the complete isolation of the computer, including USB interface, from the audio electronics, thus suppressing HF interference from the computer extraordinarily well. A direct reciprocal effect on the sensitive audio electronics is thus largely suppressed.

FAQ - frequently asked questions:

- Doesn't a galvanic isolator for the USB interface do the same thing as the Afi(s) + USB?

No. Galvanic isolation is a good basis for the neutralisation of interference, but it does not necessarily suffice on its own. Depending on the composition of the coupling element, the physical isolation of both sides could only be for a certain frequency area. Some higher frequencies can bleed through despite the isolation. Therefore our network isolator GISO, for example, is much more effective than the built-in transformer in network interfaces. The coupling is much less at high frequencies. Another difficulty with USB is that the USB always requires a direct current connection to the computer in order to switch the various operating modes. Therefore, a purely passive decoupling such as with GISO is not possible here. USB isolators thus have to contain a relatively high amount of logic or small microcontrollers that actively control this switch to override the isolating elements. This explains the relatively high price of USB 2.0 isolators. Moreover, the secondary side also needs its own power supply. Either this is a small switch-mode power supply that can on its own again produce interference or the operating power is drawn from the primary side. In this case, interference can bleed through just the same. In any case, there are two potential sources of interference on the secondary side: the micro-controller and the power supply.

The USB interface and its potentially disruptive micro-controller remains in the audio interface and is thus a third source of interference located directly in the housing of the audio device.

All three sources of interference are eliminated through the Afi+USB concept.

- That sounds brilliant, the playback quality is also considerably better than without Afi(s) + USB, but despite this, I still hear subtle differences between the USB cables and when the PC is optimised or in the case of external power supply of the USB module.

This can happen and it is no contradiction. But it is a sign of the electromagnetic reciprocal effect of the computer directly affecting the other components of the audio equipment. As mentioned above, every cable coming from the computer is a potential broadcast antenna. This electromagnetic radiation affects the badly isolated parts of the equipment. The computer definitely feeds HF interference back to the electrical grid. This can influence other audio electronics via the power supply. The suppression of the direct primary path towards the audio signal stream considerably reduces the entire problem with HF interference. Performing some corrective measures to the computer can also improve the final result. It is important to have a well-constructed computer optimised for EMC; be careful with homemade computers. Mains filters are recommended. And cables of the equipment should be connected cleanly with regard to shielding. Whenever possible, do not use asymmetrical connections, in the case of XLRs do not connect the shield to the housing contact and only connect pin 1 if devices will not function together otherwise. Built-in isolated jacks are useful to avoid ground loops. But at the same time, this always opens the door to HF interference. Also, absolutely avoid connecting unshielded cables to audio devices! Then you will surely have HF in your device and such phenomena are bound to happen.

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arfi-dac2 - artistic fidelity da-converter

24/192 digital-analog converter

arfi dac2 3D

Our first DA converter is now available. We have consciously added this development in our chronology after the afis, USB module and AD converter. The concepts introduced by the afis and USB module are necessary starting points for convincing music playback. During the development phase, the arfi-adc2 was an important "tool". Because only when the AD conversion succeeds as well as possible can the original analog signal be the valuation standard for the DA converter.

With our arfi-dac2 you can hear our many years of experience in music production and thus the sound concept of real instruments and ensembles. Comparisons to the best analog technology and vinyl records have always important to us. So basically, the result is an arfi-adc2 "in reverse". Here we also see the precisely contoured image of transients along with tonal purity and a full, round basic sound. Fine musical details, atmosphere and emotions have seldom been so audible, but the important this is: listening to music is simply an unbelievable pleasure.

The arfi-dac2 adheres to the concepts behind the afis, afi and USB module - this means: interfaces, HF interference and clocking. Therefore, we consciously go our own way, analogous to the arfi-adc2: consistently sticking to the basics. The arfi-dac2 itself has only one single input; however, since it is RJ45 Ethercon, it is a technically perfect connector and thus harmonises well with our other components. If several sources are desired, then an afis can be used additionally as a main switch. The USB connection is integrated here as well. If a USB connection is enough, then an afi+USB can also be directly connected via RJ45-Ethercon. The great afip power supply unit completes this trio and feeds both devices.

A special feature to be mentioned is the master clock input in the same format as the arfi-adc2 masterclock output. This input can be switched to use this as a clocking source. Thus the internal PLL (clock recovery from the digital signal) is avoided and PLL no longer plays a role. The DA converter directly follows the master clock of the oscillator unit in the arfi-adc2.

On the analog side, you again find, fully in the interest of audiophiles, short and simple signal paths; these are again highly sophisticated and equipped with the best components. There are several design detail decisions that differ from the mainstream. We consciously do not use DSD in the arfi-adc2 (see article "Apply the sampling theorem correctly!"). Also, we do not use user-friendly gimmicks via microcontroller and FPGA like integrated upsampling, switchable filters or the like. Computers are establishing themselves anyway as the ideal way to listen to music, and there is surely hardly a better source than the afi(s) + USB to make it possible. And this is why every form of digital signal processing should take place in the computer. Here, the highest precision with 64-Bit floating comma is possible and HF-generating calculation processes take place far away from the analog electronics and from digital sections disruptive to clocking, shielded in the best possible way. Also, music that is only available in DSD can be perfectly converted on the computer to 176.4 kHz PCM and thus as a rule this delivers better results than with a native playback with a conventional DA converter connected via USB. The moving coil indicator, which displays the sampling rate, also serves to bypass the microcontrollers. Here, we also try to concentrate on our core task - digital to analog conversion - omitting unnecessary dead freight.

Another central characteristic is the total forgoing of any type of active amplification between converter chip and analog output; no transistor, no operation amplifier and no tubes. Instead, eight converter outputs, interconnected with each other in a highly sophisticated way via two high-quality transformers to create an analog stereo signal. In our view, this is the key to music in terms of "artistic fidelity": natural sound, artistically compelling and emotionally moving music playback!

 

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arfi-adc2 - artistic fidelity ad-converter

24/192 analog-digital converter

arfi adc2

We at ACOUSENCE have over 20 years of experience in music production. We know how instruments, larger ensembles and even symphony orchestras sound live and how outstanding analog technology sounds; we still produce vinyl records. We also know which aspects of the performance of music are artistically important and crucial for the best-possible emotional intensity.

We have placed a high priority on digital issues previously mentioned under afis and afi such as interfaces, HF interference and clocking. These are a good working basis, but the ultimate discipline is of course conversion between the analog and digital worlds. Because music is played analog by the artists and music is always heard analog; the human ear functions "analog".

ACOUSENCE consciously blazes its own trail when handling the issue of AD converters: reduction to the core elements, fully in the interest of audiophiles, short and simple signal paths; these are then highly sophisticated and fitted with the best components; every detail regarding design decisions are made separately and beyond the mainstream. Our ears and the music are higher priority than measurement technology. The goal is as perfect a reproduction of the music as possible, totally in line with our ideal of "artistic fidelity".

The arfi-adc2 has increasingly established itself as the new standard among AD converters. Combined with the right DAC - like the new arfi-dac2 - the ADDA path achieves a new unmatched transparency in the case of 24/192, which means in terms of there being no difference between analog signal and doubly-converted - AD followed by DA - even with the best analog sources.

The success of the arfi-adc2 is mainly due to its very high quality, even using standard sampling rates, because these are still mostly the standard today in the studios. It should be said, however, that the preferred use is 24/192, because only then can a digital transmission path function in an ideal way. An AD converter at a lower sampler rate than 192 kHz makes as little sense as having an even higher one. Because in contrast to the commonly held and mistaken belief that the limits of human hearing can somehow be used as a natural upper limit for digital signal theory, the reality is that only the bandwidth of the useful signal is crucial for the correct application of the theory or sampling theorem. However, we know from our many years of experience with recording at high sampling rates, that standard music recordings or the spectrums of musical instruments and analog equipment before the digital phase (microphone, microphone amplifier) have a bandwidth of up to 60/70 kHz. The theory - the all-important sampling theorem - only works when a sampling rate of at least 176.4 kHz is used (for further information see our article "Apply the sampling theorem correctly!"). The exact sampling rates of 176.4 kHz or 192 kHz are correct and necessary for music, since the bandwidth of the analog signal requires this.

We totally do away with the implementation of DSD. Even if this format is being urged on by some interested circles, it makes no sense technically. The 1Bit word width was already abandoned on delta-sigma converters 15 years ago, because only multibit stages could remove crucial technical drawbacks. The arfi-adc2 works with 6Bit /12.288 MHz internally, for example. DSD is always 1Bit - whether 64fs, 128fs or 256fs - and thus around 20 years behind current technical development (for more details, read the article "Apply the sampling theorem correctly!").

Another feature which should be mentioned is the construction of the input stage without any further amplifier stages or transistor circuits. There are only passive filtering elements and a very high-quality input transformer between analog inputs and the AD converter. This unusual design has proven to be musically superior over additional amplification stages and is surely partially responsible for the unusually precise contoured image of transients, tonal purity and a full, round basic sound - as far as the analog signal is so provided, because the arfi-adc2 does not make sound; it does its job, nothing more and nothing less.

arfi-adc2 - the uncompromising converter for the highest quality music and the suitable carrier of artistic performance in front of the microphone.

 

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arfi-psu – artistic fidelity power supply unit

System power supply for all devices of the arfi series

 

arfi psu 3D

The devices of the arfi series work with DC 6-9V. The arfi-psu in housing format is an alternative to the standard mains adapter included with afis and afi. The AD converter arfi-adc2 and the DA converter arfi-dac2 are always shipped together with the afip. The arfi-psu has four 6V outputs to 4-pin XLR to power the devices of the arfi series. This is a hybrid concept, a switching power supply for AC/DC conversion followed by linear regulators, separated for each of the four outputs, thus fulfilling the requirements of the current Eco-Design guidelines. Despite this, the quality of the output voltage outdoes most traditional linear power supplies. The careful filtering of the mains connection means, in addition to good starting conditions for the AC/DC conversion, as few adverse effects on the electrical grid as possible.

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