12-10-13: Unsound
Perhaps I've been misled, but I thought the redbook standard output was 2 volts?
I haven't ever had occasion to look at the redbook specification document, but the de facto norm seems to be "full scale" (i.e., maximum) amplitudes of 2 volts unbalanced and 4 volts balanced. That would be based on the usual convention of defining balanced amplitudes as corresponding to the instantaneous difference between the voltages of the two signals in a balanced signal pair, the 4 volt number therefore reflecting each of the two signals being 2 volts.
Ralph's designs are balanced, of course, although they often provide both balanced and unbalanced inputs. I suspect that is why he mentioned 4 volts.
Best regards,
-- Al