Maintaining phase coherence was one of the main goals in the design of the Zero-One. It is our opinion that phase distortion is much more annoying than amplitude distortion because it affects the signal at a node.  While amplitude distortion causes only an attenuation (or amplification) of the signal, phase distortion gives rise to enormous relative errors when the signal should be at or near zero.

As an example, the solid line below shows a 2 tone signal (1 KHz and 3 KHz).   The dashed line shows this signal after passing through a device with 10 degrees of relative phase distortion for those two frequencies.

The signals are qualitatively different, and yet the manufacturer of such a circuit could advertise "0.000% Total Harmonic Distortion" and "perfect frequency response" for this device.  The device has effectively destroyed the phase information present in the original signal. The loss of phase coherence (which occurs with most audio equipment) is analogous to replacing a holographic plate by a photograph.   The photograph has lost the information about relative phases of lightwaves which give the hologram its three-dimensional nature. It is the preservation of  phase coherence which creates the soundstage in Daniels Audio equipment, and allows the instruments to be identified distinctly and unambiguously.

The graphs below show the amplitude and phase distortion as a function of frequency. Note that the distortion at 20 KHz is less than 1%.

In order to maintain phase coherence up to 20 KHz, and to reject digital sampling noise (at a frequency of  44 KHz * 192), an advanced 4-pole analog filter was used.  In the audio range, this filter has the minimal distortion characteristics of an amplifier with a bandwidth of 2 MHz.

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