1.  A recent ad for the Chord DAVE D to A converter claims a noise level of -180 dB. How is this possible? (Theoretically a digital black signal of all zeros would have zero noise). No electronic circuit could be this low noise; there is no way to measure it. The output impedance is rated at .0055 ohm. This does translate to a resistor (Johnson) noise of -180 dBV. However it could only be achieved with an undithered signal source , which would be highly distorted. Any real musical signal will have dither in the recording process and will have a minimum noise close to their signal to noise specification of -127.5 dBV.

Also I am skeptical since the electronics must add some noise to the low output resistance achieved by feedback. I would like to measure one.

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