It is easy to think of this from today as something like spotify or usenet, but in many ways it does not sound so far from MTV (1981) with PDC[0] and a PDC tape recoder.
He appears to describe a system of music streams which could be subscribed to (cable TV channels, streaming a winamp playlist), with an notification system that would allow a machine to tape a song (sort of like RSS/ the recording codes on VCRs[0].. this appears to be where the phone line comes in AFAICT; although that shouldn't have been necessary). I don't think he is describing anything that would use a computer on the client side, or have any 'on-demand' feature.
I read this as absolutely on-demand. Re-reading, I guess I'm making assumptions, but radio-over-phone/cable (by 'radio' I mean the 'server' transmits what it transmits and you're stuck with whatever's on currently) seems kinda dumb.
Your push concept (I say "your" because it's really not clear in the article what "subscribe" means) is a step up, but I wouldn't want to get spammed with whatever "they" decided to send me today.
Call in, dial codes for the genre, artist, album, or song; digital recorder thingy that's been listening in hears the screech of the digital stream and starts recording. Caller hangs up, recorder maintains connection until "download" is complete. In this scenario, I'd suggest that "subscribing to interest categories" just means a shortcut (less dialing) to get to music you like. You subscribe to "Hard Rock" or "Artists Similar to Queen" and you just dial less to select something to record.
My logic here hinges on "...without regard for the quantity of music he or she decides to tape" and I'll concede I might have misinterpreted his intent.
I agree it is very confusing to figure out the exact intent from the text.
In the model i suggested you would look up and input a code that referred to a song, and it would start the recorder when that song was played (working like traffic report alerts meets TiVo). No spamming.
By broadcasting real-time streams via TV you would get a bandwidth ~400 songs/day/channel (a big selection for the time). To me 'subscribing to interest categories' would be exactly like subscribing to a cable channel; and it would give you the legal right to that group of songs.[0]
It seems 'TV cable' was definitely a transmission method (very unclear if the phone was an alternative data vehicle or just for control), and AFAIK there was no way of doing anything on-demand with TV cable. To get similar quality of audio via the phone would have taken ages[1], tying up the phone for a long time (+ associated costs). The only problem with the streaming model is that you have to wait for a song to come around. But you would be able to get a newly released song right away on it's first play (and nothing was on demand at the time) so it wouldn't be a big issue IMO.
Occam's razor suggests the stream concept is most likely; it fits the existing models and technology much closer. It would have been technically simple to implement and vastly cheaper.
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0. I think this is the real 'innovation' in this, rather than delivery method, which i'm not certain Zappa was 100% on.
1. i remember 128KB songs took ~15 minutes on 56K, so we are talking over an hour, even if we ignore the lack of MP3, processing/ temp storage requirements. Remember he talks about quality. Don't forget your landline was the only real-time contact you had with people who weren't in your road.
He appears to describe a system of music streams which could be subscribed to (cable TV channels, streaming a winamp playlist), with an notification system that would allow a machine to tape a song (sort of like RSS/ the recording codes on VCRs[0].. this appears to be where the phone line comes in AFAICT; although that shouldn't have been necessary). I don't think he is describing anything that would use a computer on the client side, or have any 'on-demand' feature.
0. http://en.wikipedia.org/wiki/Programme_Delivery_Control