More than a microphone
The design problem began before the signal reached the recorder.
Dave Foister’s April 1994 Studio Sound review described AGM as having quietly developed the MR1 since 1991. The system addressed a chain of issues which classical recording engineers were debating at the time: putting microphone electronics close to the capsules, remote control of the preamps, converting to digital early, working beyond 16 bits and carrying processing in the digital domain.
The MR1 began with a tetrahedral four-capsule array. Contemporary descriptions identify Brüel & Kjær capsules; the full review specifies modified B&K 4011 capsules. The microphone electronics were kept close to the array to minimise low-level analogue cable runs, followed by early 20-bit conversion and digital processing.
What happened to the four channels
The point of retaining discrete A-format signals was that the perspective need not be irrevocably fixed at the microphone. Matrix processing, steering and output formatting could be performed later in the chain. The review describes a complete system capable of producing Ambisonic/UHJ or stereo outputs rather than a microphone whose job ended at four sockets.
From prototype to AES
An April 1993 AES product report described the MR1 Periphonic microphone as a four-channel Ambisonic-style system with 20-bit conversion and a TMS320C30-based 32-bit digital processing card. A November report says the system was introduced at the Berlin AES and shown complete at the New York AES later that year; its photograph caption identifies Dr Martin Ennis at the piano and Anthony Morris on horn during prototype testing.
Then it was used to make records
By April 1995 Studio Sound was reporting AGM’s own classical-label activity using the MR1. The first sessions included the Chamber Academy Quartet playing Grieg and Sibelius, recorded with the 20-bit system and Nagra-D recorders, plus Berlin sessions of Brahms and Strauss lieder and Ravel songs. The planned releases were under the Perfectum Est label through AGM Digital New Media.