Comparison Pro-Ject Stream Box S2 vs Pro-Ject Stream Box S2 Ultra

The sampling rate of the digital-to-analogue audio signal converter provided in the design of the audio receiver.

A digital-to-analogue converter (DAC) is an indispensable element of any system designed to reproduce digital sound. The DAC is an electronic module that translates sound information into pulses that are sent to the speakers. The technical features of such a conversion are such that the higher the sampling rate, the better the signal at the output of the DAC, the less it is distorted during conversion. The most popular option in receivers today is 192 kHz — it corresponds to a very high sound quality (DVD-Audio) and at the same time avoids unnecessary increase in the cost of devices.

Audio file formats that the receiver is capable of working with. Among those, there may be lossy compressed (MP3, WMA, etc.), lossless compressed Lossless(FLAC, APE, etc.) and Uncompressed uncompressed formats (DSD, DXD, etc.).

In general, compression is used to reduce the volume of audio files. Lossy compression (the most common option) cuts off some of the audio frequencies (mainly those that are poorly perceived by the ear), making such files take up the least amount of space. Lossless compression preserves all original frequencies; this format is preferred by many lovers of high-quality sound, however, such files take up a lot of space, and the difference between normal compression and lossless compression becomes clearly noticeable only on high-quality equipment. Uncompressed formats, in turn, are intended primarily for professional audio work; their full reproduction requires Hi-End audio equipment, and the volumes of such materials are very large. However, these standards are quite popular among sophisticated audiophiles.

Separately, it is worth touching on the uncompressed DSD format. This standard and its direct derivatives DSF and DFF use coding using the so-called pulse density modulation. It is considered more advanced than traditional pulse-frequency modulation, and allows you to achieve more accurate sound, a higher signal-to-noi...se ratio and less interference with a relatively simple element base.

— Airplay. A technology for transmitting multimedia data over a wireless connection ( Wi-Fi). Developed by Apple, it is intended mainly for broadcasting content from various Apple technology (primarily portable gadgets) to compatible external devices. Allows you to transfer audio files (in the audio streaming mode, see "Tuner and Playback" for details), as well as images, text data and even video. The presence of AirPlay in the audio receiver will allow you to connect Apple devices with support for this technology to it — for direct playback.

— Airplay 2. The second version of the AirPlay technology described above, released in 2018. One of the main innovations introduced in this update is multi-room support, the ability to simultaneously stream multiple separate audio signals to different compatible devices installed in different locations. Thus, for example, you can turn on the acoustics in the living room for training music from the iPhone, in the kitchen — a relaxing melody from the iPod, etc. In addition, AirPlay 2 received a number of other improvements — better buffering, the ability to stream to stereo speakers, as well as support for voice control via Siri.

— Chromecast. The original name is Google Cast. A technology for broadcasting content to external devices developed by Google. Allows you to tr...ansmit an audio signal from a PC or mobile device to the receiver, broadcasting is standardly carried out via Wi-Fi, while the receiver and signal source must be in the same Wi-Fi network (Chromecast media players are an exception). Chromecast technology supports two modes — the actual broadcast through special applications (available for Windows, macOS, Android and iOS) and "mirroring" content opened in the Google Chrome browser. However, the second option for audio receivers is not relevant, given the specifics of their application.

— Wi-Fi. A wireless interface originally used to build computer networks, but more recently, it also supports a direct connection between devices. It can be used in audio receivers in different formats: for network functions (streaming audio, Internet radio, DLNA, etc.), for broadcasting content via AirPlay or Chromecast (see above), and for connecting a smartphone as a remote control. An alternative option for connecting to networks is a wired LAN interface (see below), but Wi-Fi is more convenient due to the lack of wires and the ability to work through obstacles, including walls. In addition, the mentioned AirPlay and Chromecast work as standard through a wireless channel.

— LAN. Connector for wired connection to computer networks — "LAN" and/or the Internet. By itself, such a connection is less convenient than Wi-Fi (see above) due to the need to pull wires, but LAN support is somewhat cheaper, and the connection is faster and more reliable (especially when Wi-Fi channels are heavily loaded).

— Bluetooth. The technology of direct wireless communication between different devices at a distance of several metres. It can be used for a variety of purposes, but the main use of Bluetooth in audio receivers is to transmit an audio signal. At the same time, depending on the model, the sound can be transmitted both to the receiver (from a smartphone, tablet, etc.), and from the receiver to wireless speakers or Bluetooth headphones. It is believed that wireless transmission degrades sound quality, but this point is corrected in many devices using various advanced technologies such as aptX. Other uses for Bluetooth include remote control from an external gadget and file sharing between that gadget and the audio receiver's built-in memory.

— NFC chip. NFC technology is used for wireless communication over short distances (up to 10 cm). Potentially, it has many applications, but in audio receivers it is most often used as an auxiliary, to simplify the connection via Wi-Fi or Bluetooth. If there is NFC in a smartphone or other gadget, it is enough to bring it to the NFC chip of the receiver — and the devices will automatically “recognize” each other; then, depending on the settings, they will connect either automatically or after confirmation from the user. In addition, additional "chips" may be provided — for example, if music was playing on the smartphone at that moment, it will start broadcasting it to the receiver.

— DLNA. A technology used to connect various electronic devices into a single digital network with the ability to directly exchange content. Devices for which support for this standard is claimed are able to effectively interact regardless of the manufacturer. An audio receiver with DLNA is capable, for example, of playing music directly from a computer hard drive in the next room or from a smartphone in the user's hands. Connection to the Network can be carried out both wired (LAN) and wireless (Wi-Fi) way.

— USB A. The classic USB connector, familiar to most users from computers and laptops. In audio receivers, it is mainly used as an input for direct playback of music from flash drives and other drives, sometimes also for updating firmware and exchanging files between an external drive and built-in memory. Other application formats are also possible: for example, some models have a Type A output for transmitting a digital signal to an external DAC.

— USB B. This type of USB connector has an almost square shape, noticeably different from the popular USB A. The most common way to use it is to connect it to a computer as a peripheral device to control the audio receiver from a PC. However, there are other options — in particular, the use of this connector as an input for a digital audio signal.

— Card reader. A device for reading memory cards — most often various types of SD, although it's ok to clarify the specific types of compatible cards separately, as well as the possibilities for working with them. In general, this function is similar to USB Type A (see "Inputs"). Most often it is used for direct playback from memory cards, but other uses are possible — for example, copying music from a laptop to the receiver's built-in storage via a memory card.

— Internet radio. The ability to "receive" Internet radio stations using the receiver. Such transmissions are similar to conventional radio broadcasting, but are carried out not on the air, but through the World Wide Web; such broadcasting is carried out by many large radio stations, and there are also many specialized network channels. One of the key advantages of Internet radio is the lack of range restrictions, which allows you to listen to broadcasts from almost anywhere in the world and provides a wide range of choices. And for additional convenience, tools for searching and sorting Internet stations (by genres, languages, popularity, etc.) can be provided.

— Lossless formats. The receiver's support for audio formats that use lossless compression. Unlike lossy compression (in the same MP3), with this compression, the sound is not cut, all its details are preserved as much as possible. Nowadays, there are several lossless formats, including FLAC and APE; the specific set of standards that the player is compatible with should be clarified separately. However, anyway, this function will be useful to those who appreciate the most complete and reliable sound.

— Formats without compression (uncompressed). Receiver support for non-compressed audio formats. Most of these standards are professional, they provide very high quality and reliability of sound, but they also take up a lot of space. Examples of uncompressed formats include DSD and DXD.

— RS-232. Also known as a COM port. Service connector to control the audio receiver, used to connect the device to a computer or specialized equipment. Such control can provide more options than using the original control panel or remote control.

— I2S support. The presence in the receiver of an input and/or output for a digital audio signal in the I2S format. This format is mainly intended for signal transmission within audio devices, but sometimes it is also used for communication between devices; the latter is implied in this case. The I2S interface does not have a standard connector; it can use ports of various types — in particular, BNC, RJ-45 (LAN) and ev...en HDMI. Anyway, the purpose of this connector is similar to the coaxial S / P-DIF (see "Inputs", "Outputs"); while the I2S standard, on the one hand, provides higher quality and noise immunity, on the other hand, it is less common and significantly affects the cost of devices.

— Multizone. Possibility of simultaneous transmission of signals from different sources to acoustic systems located in different places (zones). For example, in a large house, you can simultaneously broadcast music from the player into one room, and a radio programme into another. Another use case for Multi-Zone is entertainment centers with several rooms of different types (for example, a table tennis room, a roller skating rink and a cafe).

— Direct connection (By-pass/Direct). The ability to feed the audio signal coming to the input of the audio receiver directly to the amplification stages, bypassing all additional controls (timbre, balance, etc.). Direct connection not only minimizes distortion in the processed signal, but also ensures that the sound is as close to the original as possible, which allows demanding listeners to appreciate the skill of sound engineers. For such a connection, either a separate set of Main connectors (see "Inputs") or a conventional line interface switched to By-Pass/Direct mode by a special regulator can be used.

— Smartphone control. The ability to control the receiver from a smartphone, tablet or other gadget with a special application. In this case, the connection is usually carried out via Wi-Fi or Bluetooth, and the specific capabilities and features of such control may be different, depending on the model. However, the app is often more convenient and visual than using a control panel or even a traditional remote control; and some functions of the receiver can only be accessed via a smartphone.

— Voice assistant. The ability to control the receiver using one or another voice assistant. It is worth noting that own voice assistants in this technique are not provided, and we are talking about compatibility with external devices that have this function (for example, with a smartphone or tablet). The most popular voice assistants nowadays are Google Assistant, Apple Siri and Amazon Alexa.

— Connecting an iPod/iPhone. Extended capabilities for working with portable devices from Apple — primarily the iPhone and iPod touch, often also the iPad. The specific set of such features may be different, it should be specified separately in each case. So, in some models, an “apple” gadget can be connected using a dock or a special cable and used as a signal source, controlling playback from the remote control or receiver panel and at the same time recharging the gadget. In other devices, the connection is made via Wi-Fi or Bluetooth, while the iPhone / iPod can work not only as a signal source, but also as a remote control (see "Control from a smartphone"). Other additional features may be provided, such as synchronizing the multimedia libraries of the receiver and the Apple device.

— mini-Jack (3.5 mm). A standard connector widely used in modern audio equipment and other electronics, mostly portable. Technically, the mini-Jack input can be used for different types of signal, but in fact in audio receivers it most often plays the role of a line interface and is mainly used to connect the mentioned portable equipment — for example, audio players.

— Amplifier input (Main). An input designed to connect an external source directly to the power amplifier (in fact, in By-pass / Direct mode, see "Communications"). In different models, the Main inputs may differ in the type of interface, most often either RCA (“tulip”) or XLR is used. The first option is extremely widespread in modern high-end audio equipment due to its low cost, simplicity and good connection quality, however, in terms of signal purity and resistance to interference (especially when working with long wires), it still loses to XLR. It is also worth noting that “tulip” connectors can also be used for the main line input — see “RCA” for details; do not confuse this input with Main (especially since they may differ in technical parameters — for example, input impedance).

— Phono. Special input for connecting turntables; often has a suffix indicating the type of cartridge that is compatible, such as "Phono MM" or "Phono MM/MC". A...feature of "vinyl" is that the sound coming from the pickup must be passed through a phono stage. Actually, the presence of the Phono input just means that the receiver is equipped with a built-in phono stage and you can connect a “turntable” directly to it, without additional equipment.

— XLR (balanced). Audio line input using balanced connection via XLR — characteristic round 3-pin plug; one input consists of a pair of these connectors, for the left and right stereo channels. A feature of a balanced connection is that the XLR cable itself dampens external interference coming to it; and the connector provides tight contact and is often supplemented with a retainer for reliability. All this allows you to achieve high quality connections and maximum purity of sound, even when using long wires. However, such inputs are rare — this is due not so much to their shortcomings, but to the fact that audio receivers are rarely used as linear balanced audio receivers.

— Coaxial S/P-DIF. A kind of S/PDIF digital audio interface that uses an electrical coaxial cable with RCA connectors (“tulip”) for connection. Such a cable, unlike optical (see below), is subject to electromagnetic interference to a certain extent, but is more reliable and does not require special care in handling. And the connection bandwidth is enough to transmit multi-channel audio up to 7.1. Note that despite the identical connectors, the coaxial digital interface is not compatible with analogue RCA (see below); and even cables for S / P-DIF are recommended to use specialized ones.

— Optical. A variation of the S/PDIF digital audio interface that uses a TOSLINK fiber optic cable connection. In terms of bandwidth, it is completely similar to the coaxial interface (see above), but it compares favorably with its complete insensitivity to electromagnetic interference. On the other hand, due to their design, optical cables are sensitive to sharp bends and mechanical stress — for example, accidentally stepping on such a cable can damage it.

— Balanced digital (AES/EBU). An interface used primarily in professional audio equipment. It can use different types of connectors, but is most often implemented via XLR. For more information about this connector and the principle of balanced connection, see "XLR (balanced)", but do not confuse these two interfaces: AES / EBU works with a digital signal transmitted over a single cable, regardless of the number of channels.

— Composite (video). An input for connecting a composite video signal. Uses the same RCA connector as many audio inputs, but is most often highlighted in yellow. The signal is transmitted in analogue format, via a single cable, which simplifies the connection, but limits the bandwidth; because of this, this standard is not suitable for working with HD. Nevertheless, it is very popular in modern video technology, in addition, it is found even in outdated devices (like VHS VCRs). Note that composite audio inputs are not provided in modern audio receivers — their role is played by standard RCA line inputs (see below).

— BNC. Bayonet type connector used to connect coaxial cable. Theoretically, it can be used for various purposes, but in fact it is most often used similarly to coaxial S / P-DIF, for digital analogue audio. BNC connectors are more reliable in connection due to the bayonet lock; there is also a version with a threaded fixation.

— Trigger. Service input that allows the receiver to turn on and off at the same time as other components of the audio system. Such an input is connected to the trigger output of a control device (for example, an amplifier), and when this device is turned on and off, a control signal is sent to the receiver. This eliminates the need for the user to separately manage the power on of each device.

— Control input (IR). Connector for connecting an external infrared remote control receiver. Such a receiver can be useful in cases where the signal from the remote control does not reach the built-in IR sensor of the receiver. Note that other components of the system that are compatible with the remote control and have IR control outputs, for example, players or tuners, can play the role of an external sensor.

Outputs provided in the design of the device. Note that for receivers (see "Type") the presence of outputs for passive acoustics is mandatory by definition, and the players, on the contrary, do not have such outputs. Therefore, the presence / absence of such connectors is not separately indicated.

— Preamplifier output (Pre-Amp). A preamplifier is an electronic unit designed to amplify an audio signal to line level. Accordingly, outputs of this type are actually line outputs for outputting sound to an external power amplifier, active acoustics, etc. For players (see "Type"), these are the main analogue audio outputs, and in receivers, Pre-amp outputs can be used in including for connecting equipment that works in parallel with passive speakers, which provides additional features for expanding the audio system. Most often, this interface uses paired RCA connectors (“tulips”), one for each stereo sound channel; less often — balanced XLR, also paired, for more details see "Inputs".

— To the subwoofer. A separate output for connecting a subwoofer — a specialized speaker designed for low frequencies. Usually uses an RCA ("tulip") interface, but there may be other options. Anyway, this output receives the signal from the crossover, which "cuts" the mids and highs, leaving the bass with which the speaker works. This simplifies the connection and eliminates the need to look for external...equipment for the normal operation of the subwoofer — for example, the same crossover (although an external amplifier may be needed for passive "subwoofers").

— Coaxial S/P-DIF. A kind of S/PDIF digital audio interface that uses an electrical coaxial cable with RCA connectors (“tulip”) for connection. Such a cable, unlike optical, is subject to electromagnetic interference to a certain extent, but is more reliable and does not require special care in handling. And the connection bandwidth is enough to transmit multi-channel audio up to 7.1. Note that, despite the identity of the connectors, the coaxial digital interface is not compatible with analogue RCA; and even cables for S / P-DIF are recommended to use specialized ones.

— Optical. A variation of the S/PDIF digital audio interface that uses a TOSLINK fiber optic cable connection. In terms of throughput, it is completely similar to the coaxial interface, but it compares favorably with its complete insensitivity to electromagnetic interference. On the other hand, due to their design, optical cables are sensitive to sharp bends and mechanical stress — for example, accidentally stepping on such a cable can damage it.

— Balanced digital (AES/EBU). An interface used primarily in professional audio equipment. It can use different types of connectors, but is most often implemented via XLR. For more information about this connector and the principle of balanced connection, see “Inputs — XLR (balanced)”, however, these two interfaces should not be confused: AES / EBU works with a digital signal transmitted over a single cable, regardless of the number of channels.

— Composite (video). This output is usually provided in models equipped with a video input of the same standard. For composite connectors in general, see "Inputs". Here also note that the role of composite audio outputs in this case is played by the main outputs of the receiver, to which acoustics are connected — in other words, the sound accompanying the video is output directly to the standard speakers of the audio system.

— BNC. Bayonet type connector used to connect coaxial cable. Theoretically, it can be used for various purposes, but in fact it is most often used similarly to coaxial S / P-DIF (see the relevant paragraph), for digital analogue audio. BNC connectors are more reliable in connection due to the bayonet lock; there is also a version with a threaded fixation.

— Trigger. The trigger output is used to automatically turn on other audio system components connected to the receiver. When the receiver itself is turned on, a control signal is sent to this output, which “wakes up” the connected device (for example, an amplifier) and relieves you of the need to turn it on manually. Of course, to use this function, the external device must be equipped with a trigger input.

— Control output (IR). The control output allows you to use the receiver's built-in IR receiver to control other components in your audio system from the remote control, such as an amplifier in another room, out of range of the remote control. With this scheme of operation, the audio receiver actually plays the role of a remote sensor, receiving commands and transmitting them through the control output to another device. Note that the very presence of such inputs and outputs does not guarantee the compatibility of various devices, especially if they are produced by different manufacturers; Sharing details should be clarified in the official documentation.