As I understand it, GRP was founded as a production company and not a record company, and when they transitioned to doing their own recordings they used digital media. GRP has never discussed their technology the way Telarc did, so I don't know if GRP was using the Soundstream system or not, but various companies (Denon, 3M, and Sony, for example) were selling digital recording equipment in the 1970s that could be used for studio recording. Sitting here looking at an early GRP CD from Dave Grusin the tagline is "The Digital Master Company, and that's what I meant by "all digital". Telarc was the same way.