Frequency range of 'preFM' King Biscuit quad reels

[furui_suterioo]

That is funny. Also kinda bogus. I have a copy of the true DS221f release from OD, and it's definitely 4.0 multichannel. The front cover artwork doesn't have the words 'ANALOGKID SHARES YES" on it, though. God knows how that one was made...a downmix from the true DS221f, then converted to mp3??

Or maybe it started from an mp3 in the first place.
Here's what a few loud seconds of the true 4.0 DS221's front left channel looks like in Audacity frequency plot. Sharpest filter is just above 15 kHz, and then another at 16.

View attachment 74014

and here's spectral view of a bit of the front left channel. I used the same settings as for the graph, but the color gain is boosted 20dB by default in audacity, so faint signal is visible up to and beyond 17kHz .
There actually seems to be *three* 'steps' in this filtered audio
- just above 15 kHz
- at 16 kHz
-just below 17 kHz

all the spiking over 17 is perhaps artefact of original analog recording, or digital processing.
.
View attachment 74016

Maybe the cutoff is present in the SQ source caused by some piece of equipment they were trying out at the time of recording. Just found downloaded the other day, figured there was something wrong when I saw total file as <200mb, haven't attempted to decode(doubt the encoding would even survive after being decoded & downmixed?)

 

[Owen Smith]

Make your own digital copy. The tape might of been from someone's personal collection dubbed from the original many years ago! I wouldn't pay that kind of money for a taped copy though!

I am assuming someone is continually running off copies and selling them one by one on ebay. If that is what they are doing then a digital copy makes more sense.

 

[Owen Smith]

Folder is titled: "Yes - Boston Garden ,KBFH(Quadraphonic) 1974 ak320"

It says "SQ Final" but the files are only 2ch mp3

It also says DS221f. That's the graphics for an Oxford Dickie DVD-A/V quad decode of that concert, but someone has included those graphics with 2ch mp3 audio. I assure you it was not done by Oxford Dickie nor with his permission, he'd be very cross about it.

 

[Plan9]

There actually seems to be *three* 'steps' in this filtered audio
- just above 15 kHz
- at 16 kHz
-just below 17 kHz

all the faint spiking over 17 is perhaps artefact of digital processing.

(Not shown: level starts to drop off at the low end at 50Hz. )
.
View attachment 74016

Sharps cut-offs like that are typical of digital lossy encoding. Nothing '1970s analog processing' about it.

 

[ssully]

Sharps cut-offs like that are typical of digital lossy encoding. Nothing '1970s analog processing' about it.

The only relevant 70s analog processing that was proposed was FM broadcast bandwidth limiting.

Questions include whether this was ever plausibly applied to the *source reels* by KBFH before they were sent to stations, or whether it is only seen when recording off the air.

I would expect an off air filtering e.g. cassette taping of the bandwidth limited broadcast, to be a bit fuzzy, plus have tape noise above it. I don't know how sharp the filtering would be if it was done by KBFH.

 

[ssully]

Another data point. On ebay I bought an authentic KBFH CD (pressed in 1999) and cue sheet that was sent to stations for broadcast during the week of January 17-23 2000. It's selections from a September 1984 Rush concert in Montreal (available now on Wolfgang's too -- the show there includes 'The Weapon' and 'Witch Hunt', both omitted from the KBFH broadcast). Presumably this KBFH show was first broadcast in late 1984 or early '85, I'm not enough of a Rush fan to know.

Here's the spectrum of one track, left channel. The thin black line is at 15kHz. The first 13 1/2 minutes at nearly full CD bandwidth (20Hz - 21kHz, with faint signal up to 22) is the Rush concert. The segments after it on the right limited to 15kHz (except the last one, which has more HF content) are advertisements - these also have virtually no content below 50Hz.