Cat's hearing or another useful property of analog magnetic recording

It can make frequencies above 20KHz audible to humans.


This may be proved as follows.


A 20Hz to 50KHz signal generator is connected to the input of a Ferrograph for example series 6 electron tube reel to reel tape analog recorder running at 7.5ips. As the machine is recording, reproduction in real time (save from tape travel delay) is head by a loudspeaker connected to the playback head amplifier. As the excitation frequency may exceed 20KHz  audible artifact tones can be heard at midrange.


So it is folding back the ultrasonic tones to the 20Hz- 20KHz audible spectrum.


So that no acoustic information may be lost.


Is this why cymbals sound like real if a recording had originally been recorded to analog tape?


The folding back is perhaps demodulation of supersonic frequencies by the ac ultrasonic bias carrier. (Beat frequency oscillator concept). 2 frequencies to a non linear system make the system produce a linear combination of those tones. Sum, difference of frequencies, multiplication of frequencies by intenger numbers and addition or subtraction between them etc, (Radio Enginnering - F. Terman). This is how we get audio from MHz modulated carrier stations. We use the non linearity of the receiving devices, (Operating feature of the Audion - E. Armstrong).


This is the same way the Theremin electronic musical instrument produces audible tones from radio frequency tones.


In fact analog tape recording may be compressing a high acoustic frequency bandwidth (spectrum) of say 5Hz - 49KHz to 30Hz-15KHz. It compresses amplitude as we know but it may compress frequency too.


So something big in amplitude and frequency (the tremendous amplitude frequency matrix of a live music signal) can then fit to something small.


Is this why the "old" recordings of the 60's sound amazing on a tiny iPad or smartphone greatly engineered internal speaker playing from YouTube?


https://m.youtube.com/watch?v=Gd2Q8VCk9co


The above track must have been recorded miking each instrument and mixing live to 2 or 3 track analog electron tube driven magnetic tape, Making Records - Phil Ramone.


Electron tubes have a bandwidth without feedback of MHz.


Input or output transformers limit this but do they do the same large to smaller place frequency or amplitude no information loss compression due to their non linearity at large signals. In fact it may be called information enhancing as the waveform is made more listenable at even difficult places such such when car driving listening to the radio.


Fortunately humanity has realized that analog systems are linear when they are needed to be (small levels) and non linear when they have to be (progressively higher levels). Like our nature.


Digital system no linearity tends to infinity as the signal tends to zero. And abruptly to infinity again after a certain high level when there are no more 1 binary digits or bits.


Nature works the other way. It uses progressive no linearity to extract as much amplitude and frequency information.


What about cats?


Experiments can be found described on the Journsl of the Acoustical Society of Aneruca where 2 tones were presented to a cat. Electrodes where then connected from the inner ear to an amplifier, loudspeaker. To the surprise of the scientists dozens of frequencies could be heard. (All the difference, addition, linear combination of those 2 frequencies is being sent to the cat's brain).


Is this why they cannot escape turning when we call them psss, psss, pssss?





General reference:


Tubes vs transistors is there an audible difference - Russel O. Hamm - JAES