Comparison Teac UD-505 vs Oehlbach XXL DAC Ultra

The presence of a toroidal transformer in the design of the device.

Such a transformer has a core in the form of a toroid (ring). It is believed that such a design reduces the level of extraneous electromagnetic radiation and minimizes the likelihood of interference from the transformer.

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 dynamic range of a transducer is defined as the ratio between the maximum signal level it is capable of delivering and the level of its own noise when a low amplitude signal is applied. Quite simply, this parameter can be described as the difference between the quietest and loudest sound that the device can produce.

The wider the dynamic range, the more advanced the DAC is considered, the better sound it can produce, all other things being equal. The minimum value for modern devices is about 90 dB, in top models this figure can reach 140 dB.

Also note that this parameter is similar in its meaning to the signal-to-noise ratio, however, these characteristics are measured in different ways; see below for more on this.

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.

Initially, the transmission of sound via Bluetooth involves quite strong signal compression, which can greatly spoil the impression when listening to music. To eliminate this drawback, various technologies are used (the most popular of which is the aptX codec, for Apple devices it is AAC). Of course, to use any of the technologies, it must be supported not only by the amplifier, but also by the Bluetooth device with which it is used.

— aptX. Bluetooth codec, created to significantly improve the quality of sound transmitted via Bluetooth. According to the creators, it allows you to achieve quality comparable to Audio CD (16-bit/44.1 kHz). The advantages of aptX are most noticeable when listening to high-quality content, but even on regular MP3 it can provide a noticeable improvement in sound.

— aptX HD. This codec is a further development and improvement of the original aptX technology, allowing to transmit sound in even higher quality — Hi-Res (24-bit/48kHz). According to the creators, this standard allows to achieve signal quality superior to AudioCD, and sound purity comparable to wired connection. The latter is often questioned, but it can be said that in general aptX HD provides very high sound quality. On the other hand, all the advantages of this technology become noticeable only on Hi-Res audio — with a quality of 24-bit/48kHz or higher; otherwise, the quality is limited not so much by the connection features as by the properties of the source files....

— aptX Low Latency. A specific variation of the aptX described above, designed not so much to improve sound quality as 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 videos or playing games, a noticeable desynchronization between image and sound may occur. The aptX LL codec eliminates this phenomenon, reducing the delay to 32 ms — such a difference is imperceptible to human perception (although for serious tasks like studio work with sound, it is still too great).

— AAC. A codec used mainly in Apple portable equipment to improve the sound transmitted via Bluetooth. In this sense, it is similar to aptX (see the corresponding points), but is noticeably inferior to it in capabilities: if the sound of aptX is compared with Audio CD, then AAC is at the level of an MP3 file of average quality. However, for listening to the same MP3, this is quite enough, the difference becomes noticeable only on more advanced formats.

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

Adjustments provided directly in the device.

— Bass adjustment. Separate bass level control; usually combined with treble control (see below). This function allows you to change the sound image by adjusting the volume of the bass sound relative to the rest of the frequency range.

— Treble adjustment. Separate treble control. Like the bass adjustment described above, it allows you to adjust the sound picture — in this case, by changing the volume of high frequencies relative to the rest of the range.

— Balance adjustment. Adjusts the sound balance between two stereo channels by increasing the volume for one channel and decreasing the volume for the other. Due to this, in the perception of the listener, the sound "shifts" towards greater volume. This function is mainly used for correction purposes — for example, if the speakers are at different distances from the listener, shifting the balance towards the far speaker allows you to compensate for the difference in audible volume.

— Level adjustment. Adjusting the overall signal level at the output, in other words, adjusting the volume. Adjusting the volume using the DAC's own control is sometimes more convenient than accessing the settings of other components of the audio system.

— Headphone level adjustment.... Headphone sound volume adjustment. This control is provided mainly for user comfort, it allows you to set the sound level in the "ears" to your own preferences. This possibility is especially relevant in light of the fact that headphones are rarely equipped with their own volume controls (and usually these are inexpensive models with relatively low sound quality).

— Sensitivity adjustment. Adjustment of input sensitivity of the converter. This function is found mainly in models with analogue inputs: it allows you to amplify the incoming signal, if necessary, even before it is processed by the converter, if the initial signal level is too low.