Audio DACs are among the most searched and purchased products by audiophiles! The reason is that the analog digital converter completely transforms the sound of the digital source to which it is connected, optical players (CD, DVD, Bluray), smartphones and computers. These devices come in different shapes. There are compacts and others with dimensions typical of other HiFi components 43cm wide. They are characterized by the presence of a considerable number of digital inputs (optical, coaxial, balanced XLR AES/EBU, USB, etc.) and one or more analog line outputs (normally transistor, sometimes with a tube output stage). The Audio DAC, in practice, replaces the source to decode the digital audio signal, performing this operation in an optimal way. Combining a good DAC with your system often allows you to change the quality of music listening for the better.

Some hints at the background of audio converters

Let's start with some story. In the 80's, the arrival of CD-Audio players and their optical disc players did not initially arouse the enthusiasm of audiophiles, who immediately complained that the Compact Disc Audio lacked realism and warmth when compared to listening to vinyl records.

The defect highlighted by audiophiles is due to the digital-to-analogue conversion section of these early players, at the time unsophisticated, which caused a considerable number of errors in the processing of the digital signal.

The reading mechanism reads the optical support and transmits the data to the digital-to-analogue conversion section (the DAC integrated in the reader itself). The data is read irregularly, however, and this leads to decoding errors and subsequent data retransmissions.

This phenomenon is called Jitter (which could be defined as a time lag between the transmitted and received signal) and is at the origin of an overlapping of musical information at high frequencies that cause the scene to be squashed and the sound to harden (which becomes more aggressive and annoying, not very fluid).

Since not all listeners are equally sensitive to this phenomenon, its resolution has been reserved only for those CD players of higher price range, where they are used a more valuable audio converter, with measures to contain and eliminate the negative phenomena of jitter.

The other side of the story is the cost of these CD players, which often exceed 2.000 Euro.

This situation, however, has generated a new niche in the HiFi market and is precisely that represented by external audio converters.

Initially produced only by the most famous HiFi brands, these new and expensive devices (called DACs, acronym of "Digital-to-Analog-Converter") are beginning to spread among the most demanding audiophiles.

Once connected to the optical or coaxial digital output of any CD player, the analogue digital converter handles audio processing more accurately and precisely, correctly synchronising the digital flow of input data and converting it into higher quality analogue audio.

Today, nothing has changed except for the fact that audio DACs are extremely inexpensive and finally affordable for everyone.

Through a USB DAC, for example, it is possible to completely transform the sound coming from a computer or from a tablet or smartphone. So, these devices can be connected not only to CD players, but to any other digital device capable of transmitting music through a digital data stream.

The DAC market is getting richer and richer, day after day, with new products, more and more performing and interesting.

The USB DAC and the importance of it being Asynchronous

With the increasing spread of digital music dematerialized from a physical storage medium (so-called digital music), the computer has become a unit of music reading very often used by music lovers.

The large data storage capacity, together with the presence of intuitive user interfaces, have favoured its diffusion also in the musical field.

Unfortunately, however, most computers are equipped with sound cards of very low quality, which are enough for a generic use but absolutely unsuitable for a qualitative listening of the music and for a serious use in high fidelity.

This is the reason why there is a growing interest in the use of Audio DACs in combination with computers, through the use of the very widespread USB connection (universal serial bus) with which all modern PCs are equipped.

In essence, the Audio DAC is a USB peripheral to all intents and purposes and is identified by the computer as a sound card.

What changes, however, is that the sound of the music files read by the computer will no longer be played through the sound card integrated into the computer, but will be decoded accurately by the external audio converter and played through its line output, which we will connect to the input of our amplifier or a pair of headphones (if the converter is also equipped with headphone input).

The advice, however, is to pay close attention to the choice of the USB DAC to connect to your computer.

In fact, it is absolutely important that the USB interface used by the DAC is Type 2 and that the converter is an asynchronous DAC.

Type 1 USB DAC converters, in fact, are extremely prone to the phenomenon of jitter and are equipped with an audio quality that can undoubtedly be improved.

On the contrary, an asynchronous USB DAC, i.e. class 2, is able to interface with the computer through a much more sophisticated and stable connection, able to contain (and often completely cancel) the problems caused by jitter and digital signal transmission errors, which are the cause of that well-known "cold and digital" sound, typical of low price CD players.

In addition, USB DACs, if asynchronous, support high resolution audio streams, with a sampling rate of 192 KHz and a depth of 24-Bit. In fact, the most recent models can reproduce music recorded at even higher sampling rates and bit depths.

There are more and more online sites that sell hd digital music, in high and very high resolution, with studio master quality, to the delight of all fans of good listening in high fidelity.

The operation of the asynchronous USB DAC is possible thanks to the presence, inside, of a communication interface that, although plug'n'play for Windows or MacOS systems, still requires the installation of specific drivers to operate with maximum performance and possibilities.

It sounds incredible, but neither Windows nor MacOS are able to natively transfer a high resolution music stream to the DAC, with bit-per-bit precision (bit-perfect mode).

Of all the operating systems, Windows is the one that has the worst management of the audio output, because of its specific architecture. The consequence is that, if you leave everything as it is standard, you get a flat, asphyxiated sound, with a crushed soundstage and no planes.

This limit, however, can fortunately be overcome through the installation of special drivers called ASIO drivers, which can be downloaded for free from many sites.

In Windows environment it is enough to install the free player Foobar 2000 and its plugin ASIO for an asynchronous USB DAC to operate at the maximum of its audio performance, with an optimal processing of the digital data stream and their conversion into analog signals to be played through an external amplifier.

Most USB DACs are also compatible with some latest generation Android smartphones and tablets, since these devices already have an operating system whose heart (the Kernel) already natively supports asynchronous USB peripherals (class 2.0) and also less sophisticated Type I ones.

Compatibility with Class 2 DAC converters allows direct reading of digital HD music (24/96).

There are also Audio DAC converters specific for Apple devices: for iPhone, iPod and iPad, but only allow the reading of music files in CD Audio quality (with frequencies of 44.1Khz to 16-Bit).

As far as the output connections of an audio DAC converter are concerned, a pair of RCAs are usually available, while on more expensive models XLR balanced outputs may also be available.

DAC Network audio: wired or wireless?

As an alternative to the direct digital connection, through an optical audio cable, or a coaxial cable, or through usb cables, the transmission between the source of the digital data stream (computer, CD player, transport, etc.) and the Audio DAC can also be done through a wired Ethernet or WiFi network connection.

Usually, these devices are independent network players, which perform very well the functions of an audio DAC.

They are much more sophisticated devices than a normal USB DAC, they have numerous digital inputs, they have analog outputs available for connection to external amplifiers, they can be controlled by remote control or even by specific apps for smartphones and tablets.

Some of them, such as the Music Server CocktailAUDIO, are the most advanced on the market can offer: in addition to the function of Audio DAC quality, these devices allow many other features including the ability to install an internal or external hard disk, to store CD-Audio through the Cd-ripping, to record digital and analog audio sources and much more.

For the communication of the audio streams through the wired (ethernet or gigabit) and wireless (wi-fi) network connections, numerous network protocols are used. Among these, the most famous and popular are Apple's Airplay (called Shareplay in Music Servers CocktailAUDIO), DLNA, UPnP, SAMBA and many others.

All these protocols allow the transfer of music streams in a "lossless" way, ie without any loss of quality compared to the original music information and, therefore, are absolutely suitable for HiFi music listening in high fidelity.

The digital data, read by a computer, a network hard disk (NAS) or a music server, is then processed and converted into analog form (and therefore listenable by the human ear) through the Audio DAC.

 

Digital transport: what it is and how it works.

As the name suggests, digital transport is a device or computer system that has the purpose of extracting and reading digital data from a mass storage device (hard disk, pendrive, optical disk, etc.).

A digital transport also has the task of synchronizing the clock (its own or of the source to which it is connected) with that of the audio DAC to which it transfers the data flow.

It has the task, therefore, to prevent and contain harmful phenomena caused by the aforementioned jitter.

The digital transport can take the form of a USB interface to be connected between computer and external DAC (for example the M2Tech Hi-Face II) or it can be integrated into a Music Server, as in the case of CocktailAUDIO.

The result of using a quality digital transport in your HiFi system is to obtain an extremely clean and stable digital signal that, through an I2S connection, or Toslink optics, or 75 Ohm RCA coaxial or 110 Ohm AES/EBU XLR, can be perfectly integrated with our external audio DAC, which can then perform the digital-to-analogue conversion in absolutely optimal and controlled conditions.

The issue of oversampling.

The oversampling technique is born in the video field, where it is called up-scaling, and is based on a mathematical procedure of interpolation of the digital data that constitute the audio signal to be processed.

For example, it is possible to up-sample a 16-Bit/44.1KHz data stream (WAV, FLAC, MP3, etc. format) into a new 24-Bit/192Khz data stream.

An increasing number of audio DACs offer this functionality, which however should not be a decisive factor in the choice of the music enthusiast at the time of purchase.

In fact, the advantages of listening to this technology are not always and necessarily obvious and, more importantly, upsampling is often a cause of jitter itself.

It is therefore certainly preferable to play an mp3 file at its native resolution, rather than having it processed through the interpolation process of the oversampling, to avoid a significant degradation of the result obtained when listening.

The importance of power supply and operational amplifiers.

One of the most important elements to pay attention to when choosing a dac audio converter is, as with audio amplifiers, its power supply section.

In fact, self-powered USB DACs often deliver lower sonic results than models that have their own power supply.

The ultimate is always the presence of a toroidal transformer in the power supply section of the DAC, since it allows to obtain an extremely stable current and to have a power reserve to easily manage the most excited and dynamic musical passages.

However, the toroidal transformer is usually present in more expensive audio converters, although there are numerous exceptions (such as Xindak and Yulong audio DAC converters).

The audible advantage is very evident: a much more convincing bass range, a natural and realistic midrange, a well extended but never annoying high range or over the top.

Very often the best audio DACs also allow the replacement of the op amps present in the output stage. This is usually the case with more complete and expensive models, and allows the more experienced audiophile to change the tone of the DAC without having to replace the entire device.

Other models of DAC audio converters are equipped with a tube audio output: in the output stage, in fact, there are one or more tubes that soften the digital sound and make it even more natural and pleasant to listen to.

How much to pay for a USB DAC?

As always, even when choosing a USB digital-to-analogue converter, you should always consider the rest of your system.

Just as it doesn't make much sense to buy a €100 DAC if you have a several thousand euro hi-fi system, so you should avoid unbalancing your audio setup in the opposite direction, for example by buying a €4,000 DAC if you may have paid €500 for the speakers; this, of course, unless you intend to improve all other audio components in the medium term.