I appreciate all the interesting replies to this thread! I hadn't looked in for a while and getting caught up now, I see several comments that are in sync with thoughts I'd had...
Terry, thanks for your perspective on the Stax / Atlantic relationship, something I had long wondered about. Even though Atlantic was big brother in a sense, the Stax records were the real standouts, sonically at least.
I want to "echo" WhyKooper's appreciation of the "dry" sound in some of these older redcordings. In contrast to what many other labels were doing, a lot of the Stax (and other R&B label) hits really had air and space. Arrangements were spare, echo wasn't overdone, and his/mids/lows kind of took turns, so the nuances, decays, and grooves were distinct and clear. I guess this approach was the exact opposite of the "Wall of Sound", which I never liked. The restrained use of echo was really a plus, it let you hear more of the natural decay of the instruments (and the studio itself, maybe). Over use of echo gets in the way of music, let's remember that it is "added distortion" in a very real sense and usually takes away as much as it adds!
JJ and Terry wrote of the Al Green mixes, and indeed, I had those in mind when I started the thread. I'd always wondered "what happened", especially with the drums. Those songs were huge smashes but even back then, even over a 5 inch speaker in a car radio, you could tell that something had gone amiss. Terry, thanks for helping to clear up an old mystery.
Bob Olhsson, you should indeed write a book. Your post had a lot of valuable answers and really addressed some of the things that have mystified me about the Motown years. Despite the almost crazy variations in overall sound and audio quality, Motown took chances, broke new ground, and got sounds that no one else dreamed of. I know that Mike McLean is a gifted and brilliant engineer who really propelled the label forward, and developed a lot of inventive recording gear and techniques. A few years ago I happened to walk the aisles of the vault where many of the old Motown tapes were kept -- boy, a lot of formats and an amazing amount of history, to be sure.
You wrote "Frankly the sound of AM radio in the '60s was frequently better than the sound of over processed FM is today" and I agree. In the late 30's, several 20kHz "wideband" AM stations operated, and in the 60's it wasn't uncommon for AM stations to go out to 12 Khz. or more. The limiting factor was usually the telco audio line from the studio to the transmitter site, which might have topped out anywhere between 5k and 15k. Of course, stations with their studios and transmitter at the same site had a great advantage. I think it was 15 or so years ago that the FCC mandated a fairly severe high frequency rolloff ("...emissions 10.2 kHz to 20 kHz removed from the carrier must be attenuated at least 25 dB below the unmodulated carrier level...") much to the detriment of AM.
Another interesting tidbit about AM is its "one-way" NRSC pre-emphasis curve. The stations boost high frequencies with a gentle curve that starts at 1k, rising to +9db at 9k, then at 10k, there's a brick wall filter. There is no complementary curve in the receiver, except in a few modern, high end sets. This was done to compensate for the poor HF response in most AM radios.
Well, getting back to the topic. I guess there were a lot of different reasons for the less than stellar sound in some of the big 60's and 70's hits but I have the impression that by the late 1970's the bugs, whatever they were had been resolved and sonic quality -- on nearly all labels, and with nearly all studios -- was much more consistent. Maybe better monitors (and Dolby, or at least the consciousness that Dobly brought to the industry) account for some of this. When I was at United/Western back then I listened closely to the releases that we worked on, and I can't think of any that had the kind of problems we've been discussing. Come to think of it though, it seems that none of the 60's and early 70's records out of United/Western, A&M, or Capital had these kinds of problems. Maybe the L.A. studios had a bit of a technological edge? Who knows.
Anyway, as JJ said, a little distortion didn't stopped those records from becoming beloved smash hits, proving once again that the music is what really matters.
Terry, thanks again for taking the time to mod here this month. I'll be sorry when March rolls around and this section shuts down. And thanks for the wonderful recordings of people like the Dramatics, Eddie Floyd, Carla & Rufus Thomas, Fredrick Knight and Jean Knight (any relation?), Johnnie Taylor, The Sweet Inspirations, The Emotions, and so many more. Twenty and thirty-somethings who aren't familiar with those tunes ought to seek them out; there's a gold mine of fabulous music from those great days.