![]() This indicates that, as expected from its use of an AD1865 DAC chip, the Audio Note's AES/EBU input truncates 24-bit data. While fig.6 reveals that the increase in bit depth has dropped the noise floor by around 9dB, of more significance is the fact that the small amounts of second- and third-harmonic distortion with 16-bit data have been replaced by much higher levels of the third, fifth, seventh, and ninth harmonics. These can be seen in fig.6, which shows spectral analyses of the DAC 2.1x's output when fed first dithered 16-bit data representing a 1kHz tone at ≩0dBFS, then 24-bit data representing the same signal. Spectral analysis of the DAC 2.1x's noise floor revealed a higher level of random noise in the left channel, with power-supplyrelated spuriae present in the right channel (fig.5). Looking at the D/A processor's frequency response with 44.1 and 96kHz data (fig.3), it appears that this filter is used to compensate for the top-octave rolloff associated with the DAC's aperture effect rather than to act as a low-pass reconstruction filter.įig.4 Audio Note DAC 2.1x Signature, wideband spectrum of white noise at ≤dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan), with data sampled at 44.1kHz (20dB/vertical div.).Ĭhannel separation was excellent, at >120dB below 2kHz, and still 112dB at the top of the audioband. However, with 44.1kHz data, the DAC 2.1x's impulse response (fig.2) is an almost-perfect delta function. This is because the player lacks a low-pass reconstruction filter, and each sample presented to the DAC chip results in a DC output voltage that is sustained until the next sample. The Audio Note DAC needs to be used with preamplifiers that have an input impedance of at least 100k ohms if the low frequencies are not to sound lean.Īs with Audio Note's CD-4.1x CD player, which Art Dudley reviewed in July 2012, the DAC 2.1x outputs a broken-looking sinewave (fig.1). ![]() The output impedance at high and middle frequencies was high, at 900 ohms, rising to a ridiculous 15k ohms at 20Hz, presumably due to the output stage being anode-coupled. The DAC 2.1x's maximum output level was 2.65V, and it preserved absolute polarity ( ie, was non-inverting). The transport's error correction is better than that required by the CD standard, but is not as good as other current transports. (This input locked to data with sample rates up to 96kHz, but not higher.) The transport began muting once per revolution of track 34 of the Pierre Verany label's Digital Test CD, which has 2mm gaps in its data spiral the CDT One/II muted completely on track 35, which has 2.4mm gaps. I also tested the D/A processor via its AES/EBU input. I measured the Audio Note CDT One/II and DAC 2.1x Signature with my Audio Precision SYS2722 system (see and the January 2008 " As We See It"), the two components connected via Audio Note's supplied S/PDIF link.
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