Tuesday, March 19, 2019
e12 Measurements
FFT Spectrum at 0dBFS
FFT (Fast Fourier Transform) spectrum of 1 kHz, 0 dBFS (2 Vrms) signal. The harmonic distortion of the 2nd harmonic at -126 dB (0.00005 %), followed by the 3rd harmonic at -127 dB (0.00004%). The higher harmonics are around -130 dB or lower. Also, note that the power line related noise (60Hz and its harmonics) is below -144 dB (0.000006%).

Intermodulation Distortion (IMD)
IMD 19K+20kHz @ 0 dBFS (2 Vrms). The 2nd order difference product appears at 1 kHz and is about -128dB (0.00004%). The 3rd order IMD products produce symmetrical sidebands around 19K/20kHz and are below-124dB.

THD + N Ratio

FFT spectrum (1024K points averaged 4 times) of 11.025 kHz signal at 44.1kHz sampling rate. This measurement exposes the smallest periodic jitters, which would appear as sidebands symmetrically located around the signal. The FFT spectrum is extremely clean, with all the artefacts around -153 dB. Only one clearly defined jitter-related double sideband is visible, located +/- 1kHz from the signal at -153 dBFS.

Noise Floor with USB Galvanic Isolation
FFT spectrum (1024K points averaged 8 times) showing the noise floor measured on the e12 DAC RCA line outputs. The e12 DAC is connected with a standard USB cable to a low-cost desktop PC. The noise floor is extremely clean. There are no visible traces from the computer high-frequency noise usually transmitted via the USB connection. The power line related noise (60Hz and its harmonics) is below -157 dB (0.0000014%).

Noise Floor without USB Galvanic Isolation
For comparison, the same measurement is taken without Galvanic ground isolation. The noise level is increased by 30dB. This experiment clearly shows the benefits of using Galvanic isolation.

All measurements are performed with the Audio Precision APx525 system, with the line outputs of the e12 DAC terminated with 100KOhms resistors. FFTs are 1024K points, averaged 8 times.

e12 DAC