Comparison Astell&Kern A&norma SR15 vs Astell&Kern AK320

The amount of built-in memory installed in the player.

This parameter directly determines how much music and other content can be stored in the device without resorting to memory cards (especially since some models do not support such cards at all). For comparison: the size of one MP3 file usually does not exceed 20 MB, the same composition in lossless format has 3-4 times more volume, a film in standard quality takes on average from 700 MB to 2.5 GB, in HD 720p — up to 5 – 6 GB. Thus, in terms of data storage, the more internal memory, the better. On the other hand, the price of the player directly depends on the storage capacity. Thus, some models are available in several modifications, differing in the amount of memory and price.

When choosing, note that part of the memory will inevitably be occupied by software firmware and pre-installed applications; sometimes this part turns out to be quite significant — for example, in models with an OS on board (see above), several gigabytes can be occupied. Also note that memory cards in terms of gigabytes of volume are cheaper than built-in drives, and from the practical point of view, in most cases they are not inferior to them. So it makes sense to specifically look for a player with a large amount of internal memory, first of all, if this model does not work with memory cards.

Now there are players on the market with such a memory capacity: up to 8 GB, 16 GB, 32 GB, 64 GB and more. However, there are also models without built-in memory, designed for use only with memory cards.

The maximum size of the memory card that can be used in the player. This parameter is directly related to the card type (see above): each type has its own volume limits. At the same time, the ability to work with capacious media is limited not only by the type of card, but also by the player's hardware. Therefore, many models have a lower capacity limit than the memory card suggests — for example, 128 GB in a model that supports the SDXC format (the theoretical maximum for which is 2 TB).

Note that the reverse situation also occurs — for example, when a device with a maximum capacity of 16 GB only supports microSD cards (theoretical maximum is 4 GB). This usually means that the player can work with newer formats (in our example, at least microSDHC), but for some reason this point is not mentioned in the official specifications (for example, the manufacturer could make a mistake in the documentation).

Model of the digital-to-analogue converter installed in the device.

The DAC is one of the key components of any player: it converts the digital data recorded in the audio file into an analogue audio signal, which is fed through an amplifier to the headphones. The quality of the DAC directly affects how accurately the output sound will match the original signal, as well as whether the player can work with advanced digital signal formats: many of them require high computing power, which is not available in every DAC.

Note that the DAC model is indicated only if it is a high-end converter with above-average sound quality. On the modern market, in particular, DACs from such manufacturers are represented: AKM, Cirrus Logic, ESS Saber, Texas Instruments, Wolfson. And players with such equipment usually refer to Hi-Fi devices(see "Type").

It is also worth mentioning that the number of DACs can be different. The simplest option is one module for both sound channels, however, there are players equipped with two converters at once — one per channel. This "division of labor" affects the cost, but reduces the load on each individual DAC, which has a positive effect on the quality and reliability of the sound.

The ratio between the level of the useful signal (clear sound) and extraneous noise, given by the player at the output. This parameter directly characterizes the quality of the built-in amplifier: it mainly takes into account the intrinsic noise of electronic circuits, and the higher the signal-to-noise ratio, the less these noises and the clearer the sound.

Note that in the case of players, this characteristic is often not particularly critical: the noise of the amplifier can be lost against the background of ambient sounds, especially in an urban environment, and for such situations even the most modest indicators, at the level of 70 – 80 dB, are enough. At the same time, for Hi-Fi models (see "Type") this moment is one of the most important; in the most advanced devices, the signal-to-noise ratio can exceed 120 dB.

Audio file formats that the player is able to work with.

— MP3. The most famous of modern digital audio formats; supported by almost all compact players, the name MP3 has even become a household name for them. Provides so-called. lossy compression, where some of the audio frequencies are lost. However, during compression, the sound is processed in such a way that it "disappears" mainly frequencies, the loss of which is imperceptible to the human ear. As a result, the sound quality can be quite high, and you can clearly distinguish high-quality MP3 from lossless format only on Hi-Fi equipment.

— WAV. Another popular audio standard, originally developed for storing sound on a PC. It can technically be used to store audio in a variety of formats, but is most commonly used for uncompressed audio. Due to this, the sound quality can be quite high, and its processing does not require special computing power. The downside of this is the large volume of audio files — many times more than MP3s.

— WMA. An audio format, at one time specially created for the Windows operating system. By default, it uses lossy compression (although there is also a lossless version of the WMA codec). WMA is particularly suitable for low bitrates, under such conditions it provides better quality than MP3 and takes up less space. On the other hand, this format is much less popular in high-quality digital audio.

...— AAC. A format developed as a potential successor to MP3. Also provides lossy compression (see above), but allows you to achieve better quality with the same file size; this difference is especially noticeable at low bitrates. Actively promoted by Apple in iPod players; nevertheless, it is noticeably inferior to MP3 in terms of prevalence, although it is supported by a considerable number of players.

— OGG. A lossy compressed digital audio format is one potential alternative to MP3. One of the key features of OGG is that as audio is encoded, the bitrate is constantly changing; at the same time, on fragments where there is no sound, the bitrate drops to almost zero (unlike MP3, where the data stream is constant, including in sections of complete silence). This makes it possible to achieve small file sizes while maintaining sound quality. Also note that the OGG format is open and not limited by patents.

— FLAC. One of the formats that uses lossless audio compression. With this compression, all the details of the original sound are preserved, so lossless formats are especially appreciated by sophisticated music lovers and audiophiles. The reverse side of this quality is large volumes of files. Specifically, FLAC is perhaps the most common of today's lossless formats. This is largely due to the fact that this standard is not particularly demanding on the processing power of the player. Thanks to this, its support can be implemented even in relatively simple and inexpensive players (unlike another popular format — APE, see below). On the other hand, FLAC files are larger than APE files.

— A.P.E. One of the popular lossless audio compression formats. Compared to another common standard — FLAC (see above) — APE allows you to achieve smaller file sizes with the same quality. On the other hand, to play such files, electronics with a fairly high processing power are required, so APE compatibility is relatively rare in compact players.

— DSD. A specific digital audio format using the so-called. sigma-delta modulation (as opposed to pulse code used in most other formats). Such modulation provides a very high sampling rate — 2822.4 kHz; however, it cannot be compared with the usual sampling rate (see above): in this case we are talking about a specific signal format. Its properties are such that DSD support can be provided even if the player's DAC formally has a much lower sampling rate. In general, this format is considered professional, its support is found mainly in Hi-Fi models (see "Type").

— DXD. Professional audio format originally created for editing DSD files (see above) — For technical reasons, original DSD is not well suited for editing. DXD uses a bit depth of 24 bits (8 bits higher than Audio CD format) and a sampling rate of 352.8 kHz (8 times higher than Audio CD). Like the original DSD, it is found mainly in Hi-Fi players.

— AIFF. Audio format developed by Apple for Macs and Macbooks; a kind of "apple" analogue of the WAV described above, also in most cases used for uncompressed audio.

— Audible. Proprietary file format used by the online audiobook store of the same name. One of the features of this format is that file playback is available only if you enter a login and password for the Audible online store; thus, supporting this standard usually means having a client programme to access the store.

This list is not exhaustive, modern players (especially the top category) may support other types of audio files.

Streaming services supported by the player.

The principle of operation of any streaming service is that music and other content is initially located on a server on the Internet and, if necessary, is broadcast to the user's device — that is, it is played, but not stored in permanent memory. First of all, streaming services are convenient for this: they allow you to access the vast collections of content without taking up extra space in the player's memory. Of course, an Internet connection is required for playback (so support for streaming services automatically means that the player is equipped with Wi-Fi — see below); however, in the modern world, this most often does not cause problems.

As for specific services, among the most popular nowadays (in alphabetical order) are Amazon Music, Deezer, Pandora, Soundcloud, Spotify, Tidal.

Codecs and additional audio processing technologies supported by the Bluetooth-connected player. Initially, sound transmission via Bluetooth involves quite strong signal compression, which can greatly spoil the experience when listening to music. To eliminate this drawback, various technologies are used, in particular aptX, aptX HD, aptX Low Latency, aptX Adaptive, AAC, LDAC, LHDC. Of course, to use any of the technologies, it must be supported not only by the player, but also by the Bluetooth device with which it is used. Here are the main features of each option:

- aptX. A Bluetooth codec designed to significantly improve the quality of audio transmitted over Bluetooth. According to the creators, it allows you to achieve quality comparable to Audio CD (16-bits/44.1kHz). The benefits of aptX are most noticeable when listening to high-quality content (such as lossless formats), but even on regular MP3 it can provide a noticeable sound improvement.

- aptX HD. Development and improvement of the original aptX, allowing for sound purity comparable to Hi-Res audio (24-bits/48kHz). As in the original, the benefits of aptX HD are noticeable mainly on high-quality audio, although this codec will not be out of place for MP3.

...- aptX Low Latency. A specific version of aptX described above, designed not so much to improve sound quality, but to reduce delays in signal transmission. Such delays inevitably occur when working via Bluetooth; They are not critical for listening to music, but when watching video, there may be a noticeable desynchronization between the image and sound. The aptX LL codec eliminates this phenomenon, reducing latency to 32 ms - a difference that is imperceptible to human perception.

- aptX Adaptive. Further development of aptX; actually combines the capabilities of aptX HD and aptX Low Latency, but is not limited to this. One of the main features of this standard is the so-called adaptive bitrate: the codec automatically adjusts the actual data transfer rate based on the characteristics of the broadcast content and the congestion of the frequencies used. This, in particular, helps reduce energy consumption and increase communication reliability; and special algorithms allow you to broadcast sound quality comparable to aptX HD (24 bits/48 kHz), using much less transmitted data.

- A.A.C. A Bluetooth codec used primarily in portable Apple gadgets. In terms of capabilities, it is noticeably inferior to more advanced standards like aptX or LDAC: the sound quality when using AAC is comparable to an average MP3 file. However, for listening to the same MP3s, this is quite enough; the difference becomes noticeable only on more advanced formats.

— LDAC. Sony's proprietary Bluetooth codec. It surpasses even aptX HD in terms of bandwidth and potential sound quality, providing performance at the Hi-Res level of 24-bits/96kHz audio; There is even an opinion that this is the maximum quality that makes sense to provide for in wireless transmission - further improvement will be simply imperceptible to the human ear.

- LHDC. LHDC (Low latency High-Definition audio Codec) is a high-definition, low-latency codec developed by the Hi-Res Wireless Audio Alliance and Savitech. The codec is also known as HWA (Hi-Res Wireless Audio). When using LHDC, signal transmission is carried out with a bits rate of up to 900 kbps, a bits depth of up to 24 bits and a sampling frequency of up to 96 kHz. This ensures a stable and reliable connection with reduced latency. The codec is optimally suited for high-end wireless headphones and advanced digital audio formats.

The player supports Bluetooth technology.

This technology is designed for direct wireless communication between different devices. There are different ways to implement it in players. The most common option is to broadcast sound to wireless headphones, acoustics or other similar equipment (aptX is highly desirable, see “Features/capabilities”). Other methods of application may also be envisaged - in particular, exchanging files with other devices and remote control (player or from the player). The specific set of additional functions should be clarified separately.

Bluetooth wireless protocols from the 4th revision and newer are relevant today:

• Bluetooth v 4.0. Revision 4.0 introduced a Bluetooth Low Energy (BLE) connection mode with low power consumption. This communication standard is intended mainly for transmitting small amounts of information - in particular, service data packets to maintain a connection. At the same time, the creators managed to combine economical energy consumption and a long communication range - it can reach 100 m, which has a positive effect on the stability of the connection.
• Bluetooth v4.1. Development and improvement of Bluetooth 4.0. In terms of players, the key innovation in this version was improved noise immunity when working near 4G (LTE) mobile communication devices (in earlier standards, Bluetooth and LTE signals could overlap, which led to failures).
• Bluetooth v4.2. Further..., after 4.1, development of the Bluetooth standard, which mainly presented a number of general improvements in the reliability and noise immunity of the connection.
• Bluetooth v5.0. Major Bluetooth update released in 2016. One of the most notable innovations was the introduction of two additional operating modes of Bluetooth LE: an increased speed mode (by reducing the range) and an extended range mode (by reducing the speed). The key benefit of these innovations is to improve the overall reliability of communications, increase their range and reduce the number of breaks.
• Bluetooth v5.1. Update to revision v 5.0, in which, in addition to general improvements in the quality and reliability of communication, it became possible to determine the direction from which the Bluetooth signal is coming. Thanks to this, the location of connected devices is determined with centimeter accuracy, which has a positive effect on the quality of the wireless connection.
• Bluetooth v5.2. The next update, after 5.1, is Bluetooth 5th generation. The main innovations in this version are a number of security improvements, additional optimization of power consumption in LE mode and a new audio signal format for synchronizing parallel playback on multiple devices.
• Bluetooth v 5.3 came into use at the dawn of 2022. Among the innovations in it, they accelerated the process of negotiating a communication channel between the controller and the device, implemented the function of quickly switching between the operating state in a low duty cycle and a high-speed mode, and improved the throughput and stability of the connection by reducing susceptibility to interference. When unexpected interference occurs in Low Energy mode, the procedure for selecting a communication channel to switch from now on has been accelerated.
• Bluetooth v 5.4 was introduced at the beginning of 2023. This edition has increased the range and speed of data exchange. Also in Bluetooth v 5.4, the energy-saving BLE mode has been improved. This version of the protocol uses new security features to protect data from unauthorized access, has increased connection reliability by selecting the best channel for communication, and prevents connection losses due to interference.

— micro-Jack (2.5 mm). The micro-Jack connector belongs to the category of TRS connections (Tip, Ring, Sleeve). The 2.5mm plug is the smallest diameter TRS plug. Micro-Jack connection (2.5 mm) is typical for mobile devices and compact portable audio equipment. The connector is backwards compatible with mini-Jack (3.5 mm) and Jack (6.35 mm), but for this you must use the appropriate adapters. Of course, when using adapters, note that the presence of an additional connection reduces the overall quality of the audio signal. To prevent degradation in quality, some MP3 players are equipped with a micro-Jack output in parallel with the mini-Jack or Jack.

— mini-Jack (3.5 mm). The mini-Jack (3.5 mm) connection is the most common type of TRS (Tip, Ring, Sleeve) interface. The mini-Jack output is found on the vast majority of consumer-grade MP3 players. The mini-Jack connector has a 3.5 mm plug — this is the middle (intermediate) type of TRS connections. The mini-Jack output is capable of transmitting an audio signal of sufficiently high quality. The mini-Jack connection is ready to satisfy the needs of both beginners and advanced music lovers.

— Pentaconn (4.4 mm). Pentaconn connection — 5-pin balanced output. Thanks to this connection, you can connect powerful amplifiers or DACs to your MP3 player. Additionally, the connector is also suitabl...e for connecting good high-impedance headphones. Pentaconn uses a larger than the mini-Jack plug, its diameter is 4.4 mm, it is stronger and more reliable than the 3.5 mm connection. The Pentaconn's balanced connection makes it possible to handle higher power audio signals. Thanks to this connection, it is possible to transmit a signal over a fairly long distance.

— Coaxial. The coaxial connection (S/PDIF) enables the transmission of an enhanced audio signal. In the coaxial signal algorithm, there is no digital to analogue conversion stage, which has a positive effect on the quality characteristics of the sound. RCA or TOSLINK connectors can be used for coaxial connection. Coaxial output is found mainly in Hi-End MP3 players. This is an expensive technique that requires the use of fairly expensive accessories. But in return, these players provide high-quality sound, designed for professional musicians and advanced music lovers.

— Optical. The optical connection is represented by a TOSLINK connector and a fibre optic cable. The essence of the optical connection is that the audio signal is converted from electrical to optical. At the other end of the cable, the optics are transformed back into digital sound. Being in optical form, the signal ceases to be subjected to interference and other interference. The optical signal does not lose its original quality even when transmitted over long distances. MP3 players with optical output provide the ability to listen to audio in high quality. The vast majority of MP3 players with a TOSLINK connector are premium models that can satisfy the needs of musicians, music lovers and advanced audiophiles.