The ES9038PRO is a premium-grade multichannel DAC chip that operates in the X18 in a configuration optimised for two-channel audio processing. The chip has its own power supply and grounding, reducing the possibility of noise from the digital circuitry affecting the sensitive analogue stages.

The carefully separated power and grounding design creates a more stable operating environment for digital-to-analogue conversion. This is particularly important when processing low-level signals, subtle details and precise channel separation, as interference from the power supply or digital control circuitry could directly affect the purity of the analogue output signal.

The Gustard X18 does not rely solely on the DAC chip's built-in processing. The unit's custom-programmed CPLD circuit manages the digital signal path, clocking and several processes that determine how steadily and accurately the data stream reaches the converter.

The CPLD handles clock management, secondary PLL processing, digital signal shaping, DoP decoding and the reduction of noise when switching between PCM and DSD formats. The purpose-built digital logic reduces the workload on the general control circuitry and provides more consistent timing for signals arriving from different inputs.

The signal at the output of the DAC chip must be converted into a voltage signal suitable for the analogue system. The X18 performs this task with separate I/V converters, so the conversion relies on precisely designed channel-specific analogue circuits rather than a single general-purpose output stage.

The unit uses eight independent I/V converters for each audio channel, incorporating low-noise, low-distortion OPA1612 operational amplifiers. The tight tolerances of the 0.1% precision resistors used in critical positions help maintain channel matching, balanced gain and accurate operation of the balanced analogue signal path.

Accurate data and precise timing are both essential for proper digital audio playback. The X18 uses two separate Accusilicon audio oscillators to provide stable reference clocks for data streams with different sampling rates.

The two oscillators identified as Accusilicon A5318-8 and AS318-B operate with jitter in the femtosecond range. Low timing uncertainty reduces temporal shifts between digital samples, resulting in more precise transient reproduction, more stable spatial imaging and more consistent digital-to-analogue conversion.

For computer-based and networked playback systems, the X18 provides a USB-B input. The USB interface accepts high-resolution PCM and native DSD data streams, allowing the DAC to work with modern music playback software and digital source devices.

USB data processing is handled by an XMOS XU216 controller supporting PCM up to 768 kHz and DSD512. This capability accommodates both high-resolution music files and sources using professional sampling rates, while the dedicated interface reduces the processing load on the DAC's central section.

In addition to wired digital inputs, the Gustard X18 also offers Bluetooth 5.0 connectivity. This allows music to be streamed to the DAC from a compatible smartphone, tablet or computer without additional cabling.

The wireless system supports aptX HD and LDAC codecs. The latter enables transmission up to 24-bit/96 kHz with a compatible source. Actual transmission quality depends on the codec support of the connected device, the wireless environment and the format of the content being played.

The X18's MQA-compatible digital processing is designed to unfold music stored in the MQA format. The process aims to deliver high-resolution information in a manageable file size and then restore the available audio data through compatible decoding.

MQA technology focuses on reducing time-domain blurring caused by digital filtering, as well as ringing before and after transients. MQA files can also be played on a standard player, while compatible decoding can unfold the encoded high-resolution layers.

The various digital filters allow the X18's time- and frequency-domain behaviour to be tailored to the system or recording being played. Differences between the filters can mainly be heard in transient handling and the roll-off of the upper frequency range.

For PCM processing, M-Fast, M-Slow, L-Fast, L-Slow, H-Fast, APO-Fast and Brick filters are available, along with NOS operation. For DSD playback, 47, 50, 60 and 70 kHz filtering can be selected to control the high-frequency cut-off point of DSD noise shaping.

The technical foundation of the X18's sound is provided by its low-jitter clock system, isolated power supply, precise I/V conversion and balanced analogue output stage. These solutions are intended to preserve digital signal timing, process low-level information cleanly and maintain accurate channel tracking.

The low-noise, low-distortion characteristics of the OPA1612 operational amplifiers, together with the tight tolerance of the 0.1% resistors, produce technically clean, controlled and detailed signal transmission, while the digital filters and NOS mode allow fine adjustment of the sound,