The D1 is the best device for improving the audio signal of speakers and headphones.
D1 is a high quality DAC / amplifier that can be used with your personal computer, smartphone, TV, etc. If you connect to D1 using a USB port or optical digital output, D1’s super-simple setup is complete without the need to install any special software.

[The best interface to connect a personal computer and an audio system] With the
D1 Premium 24bit DAC (Digital-to-Analog Converter), you can send audio signals directly via USB or optical digital output without using the sound card or headphone output of the personal computer. Can be done. D1 is the best interface to connect your computer to your audio system. Moreover, you can take the sound quality one step further. 

Audioengine / D1 product page [Various capabilities] D1 can input from USB and optical digital, and can output to any audio system including headphones. D1 DAC will give you a better music experience by using it not only with your computer but also with TV, Apple TV, DVD / Bluray player and so on. Powered by USB, the D1 can also be used as a high quality portable headphone amplifier. [To improve the sound of the computer]

D1 can process sample rates up to 24bit and up to 192KHz. With the D1, you can have a music experience with less noise and distortion that can only be experienced with high-priced DACs. With a high performance headphone output that can be used with most headphones, you will be able to have a special music experience with headphones.

[Easy setup]
Setup is easy. Moreover, no special software needs to be installed. Just connect the D1 to your device. Of course, you can connect to powered speakers like A5 + and A2 +. It is a simple design that does not require an external power supply because it is powered by USB.

[Experience the difference]
Audioengine carefully designs not only the sound quality but also the visuals. Experience the goodness with your eyes and ears. The rounded aluminum case reflects the traditional Audioengine design philosophy. In short, it offers the best sound and visuals at an affordable price. Even if you’re not an enthusiastic audiophile, you’ll know how good the D1 is.

[Specifications]
DAC type: USB and optical digital
input: USB audio, SPDIF optical digital
DAC: AKM4396
USB transfer mode: asynchronous transfer
USB controller: TI 1020B
USB class: Type 1.1 or higher
Input bit depth: 16bit, 24bit
Input sample rate: ( USB) 32kHz –96kHz (native playback) 188.2kHz / 192kHz is resampled to 96kHz
Input sample rate: (optical digital) 32kHz –192kHz (native playback)
Output: Analog RCA L / R stereo Analog 3.5mm mini jack
Output level: 2.0V RMS
Output impedance: 2 ohms
Recommended headphone impedance: 10 ohms ~ 10K ohms
Headphone amplifier : OPA2134
Optical receiver: CS8416
Playback frequency band: 10Hz-25kHz (± 0.5dB )
SNR:> 110dB
THD + N: <0.0025%
Crosstalk: -85dB
Power supply: USB 5V DC, 200mA
Size: 89mm (H) x 95mm ( W) x 25cm (D)
Contents: D1 DAC, USB cable, 0.6m, Microfiber bag, Quick start guide