The volume control uses a standard audio taper, meaning that most of the volume gain will occur during the first ½ turn. After that point the volume increase will be minimal. One small oversight is that Audioengine did not include any marks on the volume control of the D1, making it difficult to match levels. I put a couple of magic marker dots on my review sample’s volume knob so I could repeatedly matched volume settings.
The headphone amplifier, based around a TI NE5532 low noise op-amp, should be able to drive most standard headphones. I had more than adequate volume with AKG K701s, Ultimate Ears In Ear Reference Monitors, and Grado RS-1 headphones, as well as Shure SE215 and HiFiMAN RE-272 in-ears.
Near the end of the review period I had some issues with noise on some of my own 96/24 and 192/24 (downsampled on the fly) recordings played back through the D1. Problems occurred on my Apple Mac Pro Tower when multiple programs were open, and began as faint clicks that increased in intensity and volume till the selection stopped playing completely. Closing and then re-opening the music playback software usually solved the problem, but it occurred on multiple occasions with all of the music playback programs I use regularly including Audirvana, Pure Music, and Amarra.
Given its price and Audioengine’s reputation, I was expecting good, but not necessarily great, sound from the D1. My expectations were shattered (in a good way) after only a few minutes of listening. The D1 was easily better than good, and while it didn’t outperform the $3200 April Music Eximus DP1 DAC/Pre or $1495 Wyred4Sound DAC2, it did deliver nearly their level of sonic finesse. Music heard through the Audioengine D1 doesn’t sound merely decent but also is emotionally involving.
The D1’s overall harmonic balance is surprisingly neutral with little in the way of sonic bromides or extra warmth to make the sound warmer or more musical. And while the D1’s harmonic signature doesn’t warm up the sound, its lack of coloration, especially in the upper registers, makes for a very low-fatigue yet revealing presentation. For listeners who are used to the hyped-up upper registers of many inexpensive DACs the D1 may seem dark or lacking in upper-frequency air. However, I found the D1’s treble presentation to be spot on, especially on my own live recordings.