USB sound card review: ESI U24 XL

Audio performance measured

Abstract

I plan to do THD measurement of the audio equipment I design using REW and a sound card. I have the ESI U24 XL at home, which I bought years ago for a different purpose. In this article I present my findings evaluating the fitness of this sound card for THD measurement.

Measurement setup

For the measurement, the sound card was connected to my notebook using a standard USB cable.
The sound card was tested using REW 5.19 running on Debian buster. Sound card was set to 48kHz / 24Bit.
Each analog output was wired to the corresponding analog input using a short, but cheap cable. In between this connection, I will later place the DUT, that means my circuits and amplifiers processing the audio signal.

Noise floor

Noise floor is roughly between -120dB and -125dB for most of the audio spectrum. No anomalies here except the peaks at 1kHz, 2kHz and 3kHz, which are artifacts of the USB interface. For normal audio use, -120dB noise floor is okay. For precise measurements, this is too high. I would prefer at least -140dB noise floor, which in theory should be possible with 24Bit. Note that the noise floor is unrealistic for real audio applications, but results from FFT gain mostly.

THD

Above screenshots show total THD of the output and input at different levels. The uppermost plot shows THD at pretty high level. Each plot below has the level reduced by 10dB. At high level, THD is significant, reduced by 10dB, THD goes down considerably and reducing the level by 10dB again does not significantly improve THD, but worsens signal to noise ratio instead. Overall, the spectrum looks acceptable with 2nd harmonic above 3rd harmonic and all higher harmonics near the noise floor. Only the 7th harmonic has a tendency to be visible above the noise floor.

Measuring THD at 1kHz is industry standard, but USB devices may have artifacts at this frequency. Below are some plots at different frequencies:

Conclusion

Overall, the sound card appears to be a good choice for normal audio applications and should be sonically pleasing from a THD point of view. Selling for roughly 75€, this can be expected. I bought mine for 100€ in year 2013. Using the sound card for doing measurements could work in case the distortion to be measured is significantly higher. I might try a dedicated ultra-low THD signal generator instead of using the analog output together with the signal generator provided by REW. This could reduce the spectrum fed into the DUT. Overall, I like the sound card because it is small, has many interface options and works with Linux. For listening music using headphones, I prefer the sound card over the one built into my notebook.

Device information

Specification from ESI Audio (Rev. 1.1):

USB Controller

  • Chipset: ES7018L
  • Sample rate: 32kHz, 44.1kHz, 48kHz
  • USB1.1 and USB audio class 1.0 supported
  • USB2.0 Full speed compliant
  • I2S CODEC Interface, 2in/2out, Built in IEC60958 professional S/PDIF TX & RX
  • How it identifies on the USB: 0a92:00d1 EGO SYStems, Inc.

Line Input

  • Type: Unbalanced 1/4"
  • Maximum input level: +4.7dBu
  • Frequency response: 20Hz - 20kHz, +/- 0.02dB
  • Input peak LED: +3.7dBu
  • Input Impedance: 10kOhm
  • ADC:
    • Type: 24Bit, 192kHz
    • Dynamic range: 102dB @ -60dBFS A-weighted
    • S/(N+D) ratio: -92dB (@ 0dBFS, measurement method)
    • THD+N dB (A) -90dB (1kHz @ 0dBFs)

Analog Output

  • Type: Unbalanced 1/4"
  • Maximum output level: +6.9 dBu
  • Frequency response: 20Hz - 20kHz, +/- 0.02dB
  • DAC:
    • Type: 24Bit, 192kHz
    • Dynamic range: 108dB @ -60dBFS A-weighted
    • S/(N+D) ratio: -97dB (@ 0dBFS, measurement method)
    • THD+N dB (A) -97dB (1kHz @ 0dBFs)
    • Interchannel isolation: 100dB

Digital Input and Output

  • Maximum 24Bit / 48kHz
  • Type: Coaxial & Optical
  • Format: IEC-958Consumer(S/PDIF)

Linux compatibility

What I have tested successfully on Debian Buster:

  • Analog Stereo Duplex
  • Digital Stereo Duplex (IEC958) using the coax interface

What KDE System Settings offers, but I didn't test:

  • Analog Stereo Output + Digital Stereo (IEC958) Input
  • Digital Stereo (IEC958) Output + Analog Stereo Input

PCB Assembly

Circuit details

Here is some information about what I found out about the PCB assembly:

  • Mine has the PCB Rev 1.1
  • The analog audio input is built around two NJM4580 operational amplifiers. It seems, one opamp is used for signal processing, the other opamp for the clipping indicator.
  • The analog audio output is built around a single NJM4556AD operational amplifier.
  • The USB streaming controller is the TE7022L from Tenor.
  • DAC and ADC is WM8776 from Wolfson Microelectronics (now Cirrus Logic).