My father was a recording engineer in the 50's-80's. He purchased a Revox A-77 in the 60's, which was the top machine around in those days. Later in the 70's, the Revox B-77 came out and, I am told, was considerably better. These were, for the most part, considered very high end consumer machines, but Revox sold professional versions which operated at 15 ips and 7 1/2 ips 1/2 track, instead of the consumer 7 1/2 ips, 3 3/4 ips 1/4 track consumer model. The higher speed 1/2 track model saw a lot of use in simple professional recording applications, including live and location recording. Revox is a division of Studer, which makes highly regarded professional recording equipment including the tape machines which used the 2 inch wide tape running at 15 ips which were typically used to lay down 32 tracks of a recording session. The Revox machines were the first portable machines, I believe, to offer "Sel-Sync", which allowed the recording head to also be used for playback simultaneous with its use during recording. This allowed a track to be laid down and an additional track to be added later. For example, adding a later vocal track to a previous rhythm track. The Nagra machines were also very highly regarded, sonically. They were used a lot for field recording, scientific and research location work. You often see them used in nature films and documentaries for example, to record wild animals in their own habitat. All the Nagra's that I have seen were quite small and only accepted a tape reel of 3-4 inches. The Revox's accepted up to the 10 1/2 inch professional reel of tape. Generally, consumer machines machines of the 60's and 70's accepted only up to the 7 inch reels. A notable acception were the Crown machines. Later came the Akai's and others which wanted to give a professional look to their products even if they didn't stand up specs-wise and sonically to the Revox's. To my knowledge, there were no professional cassette decks, since their relatively low signal to noise ratio, poorer high frequency extension, high distortion and wow and flutter characteristics simply prevented them from being used in professional recording applications. If they were ever used, it would likely only be to determine what a particular recording would sound like on consumer equipment of the time, never would it be involved in the process of making a recording. The concept of professional cassette deck was simply a way to market those machines to the public, but I doubt there actually were any. If I were interested in vintage recording equipment, I would consider either a Revox A-77 or B-77. A recording made on one of these machines sounded exactly like the original, and the Crown machines were far inferior.
