Comparison FiiO K15 vs FiiO K17

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

DAC in this case means the “heart” of the device, the main circuit that directly provides the conversion of digital audio to analogue. The name of the DAC model is given mainly for advertising purposes — as an illustration of the fact that high-quality components are used in the device. In addition, knowing the model, you can find detailed information about a particular DAC; although in fact such a need does not arise often, it may still arise in some specific cases.

The audio frequency range supported by the device. Most often, we are talking about the frequency range that the device can output in an analogue audio signal at the output.

In general, the wider the frequency range — the fuller the sound, the lower the likelihood that the transducer will “cut off” the upper or lower frequencies. However, note that the human ear is able to hear sounds at frequencies from 16 to 22,000 Hz, and the upper limit decreases with age. So from a practical point of view, it does not make sense to provide a wider range in audio technology. And the impressive numbers found in high-end devices (for example, 1 – 50,000 Hz) are more of a "side effect" of advanced electronic circuits and are given in the characteristics mainly for the purpose of advertising. Also recall that the overall sound quality is affected by many other factors, in addition to the frequency range.

The signal-to-noise ratio provided by the converter.

This parameter describes the ratio of the volume of the pure sound produced by the device to the volume of its own noise (which is inevitably created by any electronic device). Thus, the higher the signal-to-noise ratio, the clearer the sound, the less the DAC's own noise affects the audio signal. Indicators up to 80 dB can be considered acceptable, up to 100 dB — not bad, 100 – 120 dB — good, more than 120 dB — excellent. However, it is worth remembering that the overall sound quality is affected not only by this parameter, but also by many others.

Note that the signal-to-noise ratio is often associated with such a characteristic as the dynamic range (see above). They are similar in general meaning, both describe the difference between an extraneous background and a useful signal. However, the noise level in the calculations is taken differently: for the signal-to-noise ratio, the background of the converter “at idle” is taken into account, and for the dynamic range, the noise that occurs when a low-level signal is output. This is the reason for the difference in numbers.

The coefficient of harmonic distortion produced by the converter during operation.

The lower this indicator, the clearer the sound produced by the device is, the less distortion is introduced into the audio signal. It is impossible to completely avoid such distortions, but it is possible to reduce them to a level that is not perceived by a person. It is believed that the human ear does not hear harmonics, the level of which is 0.5% and below. However, in high-end audio applications, distortion rates can be much lower — 0.005%, 0.001% or even less. This makes quite a practical sense: the distortions from the individual components of the system are summed up, and the lower the harmonic coefficient of each component, the less distortion there will be in the audible sound as a result.

Support of the Bluetooth wireless technology by the device. The main application of this technology in the DAC is wireless transmission of sound from an external Bluetooth device (smartphone, laptop, etc.) to the converter. Initially, such transmission was associated with a loss of sound quality, but relatively recently the aptX format appeared, allowing audio to be transmitted via Bluetooth without loss in quality. So when choosing a converter with Bluetooth, it would be a good idea to clarify whether it supports aptX (and, of course, this standard must also be supported by the signal source).
In addition to audio transmission, there are other possible uses for Bluetooth, such as using an external gadget as a remote control. However, they are much less common.

— Mini-Jack (3.5 mm). In this case, we mean a standard 3.5 mm mini-Jack jack used as a line output (headphone outputs that also use this connector are counted separately — see the relevant paragraph). In fact, such a connector is mainly used to connect some models of active speakers (it is especially popular in computer acoustics). In this case, two stereo channels are usually output through one mini-Jack connector at once.

— Jack (6.35 mm). Analogue audio output. Being similar to the popular mini-Jack in design (and differing only in larger sizes), this connector has a fundamentally different application specifics. Firstly, Jack (TRS) plugs are used mainly in "serious" stationary audio equipment, including professional. Secondly, outputs of this type usually operate on a "one channel per plug" basis (i.e., for example, a stereo output consists of two jacks). Thirdly, this connector often provides a balanced connection — a connection in a special format that allows you to use long wires without compromising signal quality (due to the fact that the wire itself works as a noise filter). However, a 6.35 Jack connection can be unbalanced.

— RCA. In this case, we are talking about an analogue linear audio output using RCA connectors (these connectors can also be used in other interfaces, but they have their own names). The standard output of this type co...nsists of two connectors — for the left and right stereo channels. This interface is one of the most popular in entry-level and mid-level stationary audio equipment.

— XLR. Formally, XLR is the name of the plug type; however, when talking about XLR outputs, they usually mean a specific interface — an analogue line output with a balanced connection. Such a connection (with different connectors) is widely used in professional technology; it allows the use of long cable lengths without compromising signal quality, due to the fact that external interference is damped directly in the cable. Specifically, the XLR connector is notable for its high reliability, often in such connectors locks are provided for fixing the plugs. The signal to these outputs is fed on the principle of "one channel per connector", so the standard XLR output consists of two connectors — for the left and right stereo channels.

— Coaxial S / P-DIF. Digital audio output, capable of transmitting multi-channel audio. It uses an RCA type connector, but the S/PDIF outputs are fundamentally different from the RCA outputs (see the relevant paragraph) — firstly, by the type of signal (digital, not analogue), and secondly, by the number of connectors (in S / P- DIF one connector is responsible for all sound channels). In addition, a regular RCA cable for a coaxial interface is not suitable — you need to use a shielded wire.

— Optical. Output for digital audio transmission (including multi-channel) via fibre optic cable. Such a connection is notable for its complete insensitivity to electrical interference, this is its main advantage over the coaxial S / P-DIF interface, which has similar capabilities. At the same time, optical fibre requires careful handling; a sharp bend or strong pressure can make such a cable unusable.

— Balanced digital (AES / EBU). Digital audio output via XLR connector. This connector differs from the XLR outputs (see the relevant paragraph), firstly, by the signal format, and secondly, by the fact that in this case all sound channels are transmitted through one connector. AES/EBU uses a balanced connection; such a connection makes it possible to use even fairly long wires without compromising sound quality, since interference induced on the cable is automatically filtered when receiving a signal.

— MIDI. Dedicated output for transmitting MIDI commands. It is found exclusively in audio interfaces (see "Type") that have a MIDI input (see above), and is used to transmit MIDI commands received by this input to an external device — most often a hardware sequencer or other specialized equipment.

— BNC. Coaxial connector, used primarily for digital audio transmission. It differs from the coaxial S / P-DIF (see above) not only in size, but also in the presence of a lock — bayonet or threaded — providing additional reliability of the connection.

— Trigger. Service connector used to control the power of audio system components connected to the device. When the DAC is turned on, the trigger output sends a control signal to the corresponding input of the controlled device (for example, an amplifier), “waking up” it; shutdown works the same way. Thus, the user does not need to enable and disable each component of the system separately — it is enough to enable / disable only the DAC, the controlled components will “respond” automatically.