@georgehifi Interesting. Here is a list of Patents assigned to Vimak Corporation -
https://patents.justia.com/assignee/vimak-corporationThat list includes the following patent -
Multiple clock signal generator apparatus Patent number: 5266908 Abstract: A digital-to-analog converter--preamplifier apparatus serving as an interface between a source of digital audio signal data and an amplifier is disclosed. A digital stage receives multiple digital audio signal inputs, a selected one of which is analyzed by a digital audio interface receiver, processed by a digital signal processing device and a delta-sigma modulator prior to passing to the analog stage for conversion from the digital domain into left and right channel analog audio output signals. Volume control is performed on the audio signal in both the digital domain and the analog domain in order to optimize performance and minimize noise. The present invention automatically adjust for input word lengths of greater than 18-bits. Type: Grant
Filed: January 26, 1993 Date of Patent: November 30, 1993 Assignee: Vimak Corporation Inventors: Michael A. Koulopoulos, Russell A. Siggelkoe, Thomas R. Hegg What I am certain of is that Vimak held relevant patents for the only truly discrete implementation of a Delta Sigma dac i’m aware of. And whilst they may not have invented Delta Sigma theory, they developed it to it’s ultimate potential using proprietory technology in the DS-1800Mk2.