Something weird this way comes.
I go down a lot of pathways that become the notorious rabbit hole of knowledge. Recently I bumped into a strange phenomenon about hearing. Ultrasonic hearing. Human ultrasonic hearing is a thing.
This is not some superpower of a human / dog crossbreed it is a thing in normal people.
Basically experimenters exposed people to frequencies far above 20khz. They could not identify the tone, but they did perceive something was there. Presence of an ultrasonic carrier appeared to enhance clarity in some experiments. In others it increased the comfortable listening level of some music.
This is not rigorously accepted but there is evidence depending on the study methods. Scientists have found something.
Apparently they already knew that with bone conduction relatively normal people can perceive 28khz. Some of these other experiments used over 40 khz and up to 120khz. Crazy right?
Where am I going with this? My hearing taps out at 12 khz last time I checked. In my not-at-all-rigorous comparison tests of streaming I think something is missing. What if this something is ultrasonic?
My preamp is rated at the line level to 200 khz. The phono is rated to 40khz. My ARC Cl60 is rated to 40khz. My phono cartridge is good to over 40 khz. My speaker tweeter will go to 40khz but response drops rapidly. If there is something on the source it can get through.
CDs and Streaming signals have filters to block signals above the Nyquist frequency of 20 to 22 khz. DACs have to filter ultrasonics hard. Ideally as I understand it nothing above those frequencies is even on the source.
Note that I and most others who prefer the sound of a good LP use that word "prefer." In these experiments subjects also prefer sounds with ultrasonic content.
Old school speakers often had "super tweeters" that work far above 20 khz. People liked them.
We know normal human limits from anatomy. The size of the tiny hairs in the cochlea and the mechanical characteristics of the hearing mechanism. It aint just beep tests into headphones.
We also know that frequencies can interfere with one another, modulate, and beat on each other. Is there some kind of modulating happening? Say two ultrasonic signals modulate each other and create an audible signal.
This has already gone deep into the math I do not feel comfortable with.
Is it possible that LPs have some ultrasonic content? I know DMM cutting modulates the cutter with I think 45khz to facilitate the cutting process. I have heard some lacquer cutting does that as well. Analog systems can record frequencies above audible. Double the tape speed of a Reel to Reel deck and arguably double the frequency response. 30ips tapes sound better you know.
The famous Sheffield Direct to Disc albums sound more clear and real. Is it because there is ultrasonic information in there? An FFT analyzer could find it. I am not that much of a geek or rich enough to have one.
It would be so cool to show that there is a reason to prefer LPs aside from just liking them.
