Measurements
Usual caveat: Measurements are merely slices of reality. They can never encompass the full reality of listening experience. Yet when properly interpreted, they do reveal underlying physical mechanisms that correlate, to a limited degree, with listening experience. With the recognition of their limitations and capabilities, they can be a useful guide in evaluating the performance of audio equipment.
FFT Spectrum @ 0 dBFS
FFT (Fast Fourier Transform) spectrum of 1 KHz, 0 dBFS (2 Vrms) signal. The harmonic distortion is dominated by the 3rd harmonic at -118 dB (0.00013 %), followed by the 2nd harmonic at -123 dB (0.00007 %). The higher harmonics are around -130 dB or below, the limit of the measurement equipment. Also, note that the frequency spectrum is free from power line related noise, i.e., 60Hz and its harmonics.
FFT Spectrum @ -140 dBFS
This measurement with a -140 dBFS signal reveals the DAC's ability to resolve the smallest signal in a 24-bit system. Neither averaging nor dither was used in the FFT in order to expose the raw performance of the DAC. The -140 dBFS signal is clearly resolved, well above the noise floor.
Intermodulation Distortion (IMD)
IMD 19K+20KHz @ 0 dBFS (2 Vrms). The two tones at the upper limit of the audible range push the DAC's ability to track high-frequency signals. The 2nd order difference product falls at 1 KHz and is around -127dB (0.00004%). The 3rd order IMD products produce symmetrical sidebands around 19K/20KHz and are about -130dB or below.
Jitter
FFT spectrum of 11.025 KHz signal sampled at 44.1KHz. Very long FFTs, 1024K points averaged 4 times, bring out the smallest frequency-coherent jitters, which would manifest itself as sidebands symmetrically located around the signal. The FFT spectrum is clean, with all the residues around -150 dB. Only one jitter-related double sideband is visible, located +/- 1KHz from the signal at -150 dBFS, For more details about jitter measurements, read "Measuring Jitter".
Crosstalk (Channel Separation)
The D1 DAC shows near ideal channel separation. The crosstalk is below -130 dB for most of the audible frequency range, increasing only sightly at 20KHz.
Headphone Amplifier
FFT spectrum of the headphone amplifier output, with a 1 KHz, 2 Vrms signal into a 60-ohm load. Its characteristic is similar to that of the line-level output. The harmonic distortion is dominated by 2nd and 3rd harmonics, each around -116 dB.
Signal to Noise Ratio (SNR)
Often, the SNR is specified only at the maximum level, but most people listen to music at a much lower level, with the volume control typically between -20 and -10 dB (between 59 and 79 on the D1 DAC display). This plot shows the actual SNR that can be attained at realistic listening levels.
FFT with Volume Control at -20 dB
FFT spectrum of 1 KHz, 0 dBFS signal attenuated 20 dB using the volume control. D1 DAC's volume control, implemented with an optimal combination of 32-bit digital attenuators and thin-film resistor dividers, assures that digital artifacts are not introduced even at low volume levels. No artifacts due to the digital volume control is visible in the FFT spectrum. The only significant residue is the 3rd harmonic, 120 dB below the signal.
Notes on Measurement Condition:
- All measurements are performed using the Audio Precision APx525 system. The line outputs of the D1 DAC were terminated with 100Kohms. Unless otherwise indicated, FFTs were 64K points, averaged 4 times, with the AP-equiripple window.
- Each unit is shipped with a detailed printout of measurements. See an example of the measurement summary.