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 -118 dB (0.00013 %), followed by the 3rd harmonic at -120 dB (0.0001%). The higher harmonics are around -130 dB or lower. Also, note that the power line related noise (60Hz and its harmonics) is below -145 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 -142dB (0.000008%). The 3rd order IMD products produce symmetrical sidebands around 19K/20KHz and are around -130dB or below.
THD + N Ratio
THD + N Distortion Product Level
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 -152 dB. Only one clearly defined jitter-related double sideband is visible, located +/- 1KHz from the signal at -152 dBFS.
Noise Floor with USB Galvanic Isolation
FFT spectrum (1024K points averaged 4 times) of the e20 DAC connected 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 -155 dB (0.0000018%).
Noise Floor without USB Galvanic Isolation
For comparison, the same measurement is taken with the PC ground connected to the DAC ground. The noise level is increased by 30dB. This experiment clearly shows the benefits of using Galvanic isolation.
FFT Spectrum at -140 dBFS
FFT spectrum of 1 KHz, -140 dBFS signal, A-weighted. This measurement illustrates the DAC's ability to reproduce the smallest details in a 32-bit system. The -140 dBFS signal is clearly resolved above the noise floor.
Headphone Amplifier - FFT Spectrum at 1 Vrms
FFT spectrum of the headphone amplifier output, with a 1 KHz, 1 Vrms signal into a 60-ohm load. The harmonic distortion of the 2nd harmonic is around -120 db, and the 3rd harmonic is around -106 dB.
Headphone Amplifier - Intermodulation Distortion (IMD)
Headphone Amplifier - THD + N Ratio
Headphone Amplifier - THD + N Distortion Product Level
All measurements are performed with the Audio Precision APx525 system, with the line outputs of the e20 DAC terminated with 100KOhms resistors. FFTs are 1024K points, averaged 4 times.