Testing & Results
The EB01-E USB DAC was tested for noise and distortion using audio content with a range of sample rates and bit depths, including a 44.1 kHz sampled 1kHz tone as the input.
The 1 kHz digitally generated sine wave was used In order to measure the signal-to-noise ratio. By observing the frequency spectrum of this signal at the EB01-E analog output it is straight forward to determine the inherent noise and distortion.
The EB01-E was also tested with two pairs of headphones ranging in impedance from 32 ohms to 150 ohms directly at the analog output. Subjective listening tests consisted of a variety of acoustic and electronic material from an iTunes library using both the USB and optical digital inputs
Audio comparison DAC: MBOX DAC (24 bits, 48kHz sampling)
PC Platform: :Windows 8.1 PC 64 bit
Audio Program: Adobe Audition CS6
- Low impedance headphones: BeyerDynamic T5p (32 ohms)
- High impedance headphones: Sennheiser PC350 (150 ohms)
- Audio Test Material 1: 1 kHz sine wave 24 bits, 44.1kHz
- Audio Test Material 2: iTunes AAC encoded
- Audio Test Material 3: 96kHz 24 bit WAV music audio file
The analog output of the EB01-E was connected to an ADC with a sample rate of 96 kHz and a sampling depth of 24 bits. The measured noise floor of the ADC was approximately -110 dB with the ADC input grounded.
A number of initial tests were run with EB01-E sample rates and bit depths ranging from 16 bit/44.1 kHz to 24 bits/192 kHz. It was observed that in all cases the EB01-E output noise floor did not drop below 100 dB, suggesting that the output analog noise floor was dominated by the output stage op amps noise.
The output of the EB01-E is shown below with a 1 kHz tone sampled at 44.1 kHz and 24 bits. This lower sample rate is shown to provide greater detail of the audio baseband.
One very good reason to include an outboard audio DAC in computer system is to reduce the amount of analog cables connecting the PC to the audio system.
For example, I was running approximately 8 feet of standard stereo cable pair from my computer’s analog output to the ADC used for these tests. The frequency response of this output with the same 1 kHz tone is shown below.
Although this measurement only shows the audio response of one arbitrary computer set up, the key point is that measurable and potentially audible noise is definitely introduced when analog audio is routed rather than digital audio.
Subjective Listening Tests
After using the EB01-E as my primary audio source for several weeks, I did not encounter any glitches or audio artifacts with the USB audio input. I tested a range of audio source material including 192 kHz 24-bit sampled audio, Blu-ray audio and the range of compressed music formats. The output noise floor of the EB01-E is below the typical listening threshold when played at normal volume.
It’s interesting to note that in carefully controlled experiments (SACD), test subjects listening to audio did not have great success distinguishing between audio encoded at 16 bits and 44.1 kHz and the higher sample rate and bit depth content. What this means is that in most cases the EB01-E can be enjoyed at a standard 16-bit and 44.1 kHz sampling rate without fear of missing something in the audio. However, for those listeners who demand the peace of mind provided by the highest audio sampling rates, the EB01–E is more than capable of delivering the content.
A pair of headphones was connected directly to the audio output of the EB01-E using the included headphone adapter, and a wide range of audio material.was played using all three digital inputs.The volume was controlled on the PC, and the resulting audio was surprisingly good considering the lack of a dedicated headphone amplifier. This is a workable use case for the EB01-E, however the lack of a physical volume control within quick reach could result in a few loud jolts when listening to music.
In fact, care should be taken when switching digital audio sources with the rear SW button. You really have no way of knowing for sure what the source volume is, and it’s entirely possible to switch to an uncontrolled and unexpected high volume level. For this reason, caution is recommended when switching audio sources using the SW button when headphones are directly connected.