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!

maynovent

Showing 1 response by mceljo

@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.