Question about how analog audio recording works
Hello!
My wife and I are high and having a discussion about how sound is recorded on records. I have an, I think, more than average understand of how sound and recording/playback works so I was trying to explain how grooves on the record represent sound waves.
What we don't understand is how polyphony is physically represented. So I can see how a single sine can easily be represented on a record. But when you're talking several sounds at once, some on the same pitch some now, dozens of timbres happening all at once, how do we differentiate those sounds on a physical medium like vinyl, or how do we represent it digitally? Is it literally nothing more than 1s and 0s? That'd be sick
Anyway, I hope this makes sense. Thanks!
It's the Fourier Theorem. The same math that makes the 1s and 0s work in digital also explains the squiggly grooves in an LP. |
In air, there's no such thing as polyphony. Air pressure is either rising or lowering. The sound of a violin, or drum, or any complex sounding instrument at any instant in time is creating pressure at a microphone which is either going up or going down or still when silent. That up and down is what a vinyl record tracks, and what a speaker driver represents as it moves towards you or away from you. |
@dweller Full range drivers are not an example. They fall all over themselves all the time due to breakups and something called the Doppler Effect. Finally, 'full range' drivers don't exist. All of them will need a subwoofer and a tweeter (to fix beamy-ness); in essence 'wide range midrange driver' is a far more accurate description.
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Compact discs do not have 1's and 0's embedded in the polycarbonate. CDs have a series of pits on an aluminum layer arrayed in a spiral pattern. A red laser follows the spiral groove from the center outward. The reflected laser light is read by a photo detector which converts the light into varying voltages according to intensity. The data on the CD is encoded by the different distances between the pits. These distances are called "lands". A transition between a pit and a land can be either a 0 or a 1. It is the transition between pits and lands that is the basis of optical data encoding. |
@atmasphere : The Lincoln Walsh speaker is the closest to being a full-range driver of all the dynamic (moving voice coil in a magnetic gap) speakers. It does have a problem with frequencies above 8khz being down in level compared to the midrange. John Strohbeen at Ohm in Brooklyn added an upward-firing dome tweeter atop the Walsh cone crossed over at 8khz to compensate for this. I think this is a successful approach! I have a pair of the older Sound Cylinders and they do sound spectacular! |
Science rules !! Just conceptualize the various process involved from capturing the music to making the disc (cd and vinyl) to playback thru a system. Here is the very first recording ever made from France"Au clair de la lune" 1861.www.firstsounds.org/sounds/Scott-Feaster-No-36.mp3 The march of science. |
I’ll bite. In any analog medium, waves are superimposed on each other. For example, in water you could have small high frequency waves and large low frequency waves and what you would see would be big waves with multiple little waves on top of them. For sound waves it is basically the same. Imagine a line with a bunch of small wiggles in it. Now imagine the whole line being bent (with those small wiggles still intact) into a much more gradual, large wave. Now you have the visual equivalent of two tones — a low tone represented by the broader up and down and a high tone represented by the smaller wiggles superimposed on the broad up and down. If you looked closely at the groove of a record you would see this same thing. A mono record is easier to see it since it is a one dimensional wiggle. You would see a broad gradual wave in the groove, with a smaller, more closely spaced wiggle in it. The cartridge translates this to an electrical signal, which gets boosted in stages before it gets translated into driver motion, passes through the air as compression waves, and then translated back into motion at our ear drum. We then perceive this as two separate tones because we have hairs in our ears that are tuned to different frequencies, and those nerves send differentiated signals to our brain, which does some amazing magic to process those signals into the perception of hearing a two tone sound. |
For all purpose in life and for the average "us" the above post is enough... But to goes further the links i put are very illuminating about the complexities of this problem...
By the way in an audio system well put and under control, we "see" the sound in the room, our brain translate chords into imaginary perceived but very real dynamical VOLUME... It is like a rainbow perception a "real" illusion not a misperception, or an error or a meaningless accident but a phenomena at the frontier where the mind encounter the world and translate it from inside ... My K340 headphone did this as well as my speakers in their acoustically controlled room did it , then sound is not only an abstraction created by the brain and the wacves, not only a felt vibrating string on a plane , nor a mere vibrating and oscillating surface, but a volume too and more...Acoustic and psycho-acoustic are so deep that even today there exist many unanswered problems about hearing ... For example this articleabout decoding perception by the brain: https://phys.org/news/2013-02-human-fourier-uncertainty-principle.html Readers of the Bible know that the first sound play the first role in the creation in "Genesis and in ST-John where Logos is not an abstraction only but a "sound" and a "voice" ...As in Indian vedas the sound "OM" contains the universe... This is not only mere superstition but deep spiritual intuition about sound...And Sound contain information and memory as Babies listening the world decipher it way before seeing it... Etc.. Sound qualities are heard and convey many information about the fruit if we tap it to know if the fruit is ripe or not...We can deduce hearing his sound if the tapped object is made of steel or wood and if he contains aperture, one or many, and if the object is empty completely or dense etc... Sounds is information not a mere wave abstraction...Sound is quality not only quantity... But anyway numbers are qualities too as in Pythagoreanism and Platonism for example through their connection to shape and then qualitative symbolism by a primal Cenesthesia...
To answer this question mathemathically is very hard....Most of the question and some answers can be found in Marc Kac article," Hearing the shape of a drum" and there is an interesting and very deep confrence by Alain Connes, a true genius, founder of non commutative geometry...Keep his French name in your mind if you are a young student in physics or maths... here the wiki stating the maths problem in two paragraphs: "the shape of a drum" https://en.wikipedia.org/wiki/Hearing_the_shape_of_a_drum
Marc Kac article put the problem in front of your eyes: https://www.math.ucdavis.edu/~hunter/m207b/kac.pdf Now deeper and life changing but very hard to figure out if you are not a physicist or a mathematician, Alain Connes go under the belly of this question and think about TIME and Information among other matter in this conference title "Seiing shapes" ... It is translated in English from the french original...Very deep...I must listen to it anew because it is very hard and i forgot it after few years...( i am a philosopher not a mathematician but maths is one of the key to philosophy for me) |
Yours is a question that you can see the answer or you can’t. Some people’s brains are geared differently and they can see things. Take Albert Einstein, he figured out the theory of relativity in his head! And with all the computers we have now, we still can disprove it. How did they figure out the speed of light so he could figure out his equations? How does AM radio work? Is it the same as FM radio? (No). Stay curious! |
My wife and I are high and having a discussion about how sound is recorded on records. I have an, I think, more than average understand of how sound and recording/playback works so I was trying to explain how grooves on the record represent sound waves https://showbox.bio/ . What we don't understand is how polyphony is physically represented. So I can see how a single sine can easily be represented on a record. But when you're talking several sounds at once, some on the same pitch some now, dozens of timbres happening all at once, how do we differentiate those sounds on a physical medium like vinyl, or how do we represent it digitally? Is it literally nothing more than 1s and 0s? That'd be sick
i got this... |
@mahgister , WELCOME BACK! I won't ask where you have been, curiosity can be fatal. This is not a problem of math. Math is a way of describing the problem. I believe it is a problem of conception not a problem in and of itself. It is reality and the proper use of electrons, physics and acoustics by people who can conceive of these issues. The beautiful thing about humans is we all have different talents. My understanding of math is very limited, but I can design in my head what people think is beautiful furnisher. Enjoy the Music and forget about the questions. Curiosity is fatal. |
Thanks for your kindness mijostyn , I was sometimes rude when we discussed in the past... I am too much passionnate and not so wise ...i am happy to be welcome by you... And i am happy to discuss with you even if we will differ of opinion in the future...but very opposite perspective are helpful to us and to all .. I was sad and very busy selling my house then loosing my acoustic room depressed ... This impacted my health...I sell the house by force not by my own free will... My new house is smaller... No acoustic dedicated room... 😥 Then i decided to go back to headphone not so happily because my room was spectacular...and none of my headphones ( 9 ) ever pleased me except the last one i never optimized because of my room spectacular acoustic.. but i stumbled on this headphone not easy to figure out and i take 6 months of daily listenings experiments to modify and optimize it ( 6 modifications) ...Surprizingly , it goes under 30 hertz and then the soundfield i reach rival my speakers which stayed at 45 hertz or 50 at most...The AKG K340 is the top headphone of 1978 and is always top today ( modulo optimization) It is not an headphone i will advise to everybody bec ause you must be ready to open it and to created a DEDICATED system only fot it ... I lost my "mechanized equalizer" 😁 but i used an electronic equalizer as you do yourself to optimize once for all the k340 my hybrid headphone...This k340 is the most difficult headphone and the most picky ever to drive and i even read the Dr. Gorike patent to figure it out how to optimize it ... Then my house sold, my health coming back , my new audio system ready, i missed all people here and decided to go back... I wish you with my heart the best possible for you and your family...
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@maynovent - Your question is a difficult one to visualize and, I think, the seed for a lot of misunderstanding and even pseudoscience in the audiophile world. I’m far from an expert, but have spent quite a bit of time trying to make sense of things. I think "visualizing" the analog process is the easiest way to understand it. Sound waves cause a microphones diaphragm to move in and out which creates an electrical signal that is a series of +/- voltages that will eventually cause the speaker drivers to replicate the in and out pattern of the original sound wave. A - negative voltage at the speaker makes it move one direction and a + voltage makes it move the opposite direction. Lower notes have longer wave forms so the speaker driver has to move farther in each direction to replicate it. Where it get’s harder to think about is when there’s more than one frequency because it’s hard to imagine a single driver replicating more than one frequency. In reality, the drivers can replicate high frequencies (think a vibration) at the same time as a deep bass note (think about when you an actually see a bass driver moving). In the end, the audio signal is really a series of positive and negative voltages that in super simple terms could be visualized as you taking one step forward and then one step back (representing a higher frequency) while standing on a moving belt that was simultaneously moving you forward 5 feet and then back 5 feet (representing a lower frequency). In the end, your absolute position (representing the driver) is what creates the combined sound wave. I’ve seen a great YouTube video that showed what multiple sounds looks like on an oscilloscope, but I can’t seem to find it today. I think a lot of audiophiles believe that cables are literally carrying a lot of music signals in parallel when it’s really just one signal. Something like a tuning fork will result in a nearly perfect sine wave while a full symphony will have a very complex wave form that is still just a more intricate series of positive and negative voltages. Without getting into the cable controversy, it’s important to recognize that music is not flowing through cables and it’s instead just a series of alternating positive and negative voltages of varying amplitudes. When it is thought about in this way, it’s easy to understand how maintaining the timing and amplitude of the pulses in the electrical signal are critical. The concept of "bandwidth" is, I believe, often mistakenly thought of as being able to pass more signals through in parallel and you’ll see a lot of the advertising capitalizing on this misunderstanding.
Think of an ideal audio system acting a rigid connection between the microphone diaphragm and the speaker driver. Every movement in the diaphragm should be perfectly translated to the speaker driver. |
@mahgister , adaptation is the key to human survival. What are you driving your headphones with? Triodes seem to be the thing now a days. |
Yes we must adapt but without cooperation ( my wife and doctor) first no adaptation will be useful very long ... I admire Darwin not the neo- Darwinians... If i can tease you... 😉 i begins to drive them with my beloved Sansui Au-7700 which was driving my speakers with an organic almost tube-like sound but it is as you know an S.S. design... The AU-7700 is one of the best Sansui but the K340 are not only hungry, but very picky and revelatory of noise more than my speakers was , and i discovered that what was acceptable from my speakers Mission Cyrus in my room was not acceptable by the AKG K340... Too high noise floor from the Sansui Au 7700... I then swithch toward the top Sansui line the alpha series... i pay 300 bucks for this Sansui alpha AU 607-i ... This one is not as a tube-like sound but it sound more S.S. ,more cold than warm, from my speakers when i connected it to them it sound the same from the K340... More cold but with my speakers i prefered the Au-7700 ...But it was i needed for the K340... There exist better amplifier no doubt even if it was the best of Sansui in 1987...But my budget is very limited... https://audio-database.com/SANSUI/amp/au-alpha607i-e.html Anyway after 6 modifications inside and around the AKG K340 which takes me 6 months of listening experiments ( because i learned how this hybrid with passive grid of 5 resonators inside creating a dual acoustic chamber in the shell must work optimally i even read the Dr. Gorike patent to do it) ... After my long process of optimization i was very satisfied by my soundfield 3-D filling the room as speakers did in many recordings... This is the only successful hybrid in history and a complex design to figure out if we want to optimize it... My dreamed amplifier is the Berning ZOTL tube amp , because of price, and because tubes in it have a 10,000 hours life span and stay always cold as temperature of the room ... And the K340 need more a cold sound as in S.S. to my ears to shine than a warm one to shine... And the tube amp of Berning sound more like S.S. with no harshness though... I never listen to it but i read all reviews.. I am completely satisfied now with the Sansui alpha... But i dream to try the ZOTL...It is not necessary... My actual system is better than my speakers/room on many acoustic factors because my Mission Cyrus so good they were for their price and they were good , lack deep bass and did not have the electro-static high frequencies i can enjoy now... And because of his inside grid of passive Helmholtz resonators able to fool the brain, i enjoy out of the head and speaker like realistic sound.. If i listen big organ , the organ is not in my head, the organ fill the roo0m and i feel it with my body and feet at 30 hertz by bone resonance... It is incredible and no headphones i own (9) would even compare... I dont use them... And now being no more sad with the lost of my room and in better health,my house sold, i came back here again... By the way the atma-spehere tube amplifier is spectacularly beautiful and the reviews are unanimous for sound quality...Congratulations! But it is double the price of the ZOTL amplifier which i cannot afford anyway and i will never be able to pick one and the other for comparison... But there is no frustation, my actual low cost system is anyway at 600 bucks the best i ever heard and i cannot fault it... i will keep my illusions and invest money in music... i did not bother myself with sound anymore and the 3-D sound effect out of the head i was liking in my room is now around me again differently but not in a bad or worst way at all with this headphone... My best to you...
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