Note I’m not talking about literal voice transmissions as those are apparently by a speaker capturing the sound and basically transmitting the instructions of how to move the speakers to replicate it.
But I’m talking about data and telemetry transmissions. There’s videos of some of the early satellites “sounds” which are their telemetry transmissions somehow being converted into pure sound?
You can represent most data transmissions in audio. With digital transmissions you can just, well beep really fast, with 'beep' =1 and 'no beep' =0
Sputnik 1 would transmit on 40 and 20 megahertz, and you could hear it's transmission beeps with a radio, even without the device you'd want to decode the telemetry data.
It’s exactly the same principle as transmitting voice/sound: you encode the signal you care about by varying some properties of the carrier wave, such as the amplitude or frequency. Then on the other end you undo that to get back the signal. If the signal is in the frequency range that’s audible to humans, you can simply feed that into a speaker and you’ll “hear” it
Morse code is probably the simplest example of how data can be represented by sound.
Hum a steady tone, say an A at 440Hz, that's your so called "carrier frequency" or "carrier signal". If you want to transmit a "1", you hum 100Hz higher for a second, then hum at the carrier frequency for at least half a second. If you want to transmit a "0", you hum 100Hz lower for a second, and then at least .5 seconds of the carrier frequency again. If you want to transmit two of the same symbols on a row (e.g. "00") that's where the .5 second interval of carrier frequency comes in, to separate both 0s from each other. You just did Frequency Modulation.
If you tune into a radio station at say 92.4MHz, that's the carrier frequency you're tuning into. The actual sound is called the "baseband signal". If you want to transmit, say, a 1Hz sine wave as a baseband signal over the carrier frequency, you would raise and lower the carrier frequency above and below once a second. How far you raise and lower it is called the bandwidth, the more bandwidth, the more data you can fit in the signal.
At the receiver, it's easy to filter out the carrier frequency and obtain the change of frequency from the signal, which is our 1Hz sine wave baseband signal.
This is just one of the methods how a baseband signal can be modulated onto a carrier frequency. Instead of the carrier signal frequency, you can for example manipulate it's amplitude. That is, for example, a "loud" burst of carrier frequency is a "1", and a quiet one is a "0". You can also manipulate the phase of the carrier signal. If you look at a sine wave and always take a measurement at its frequency (e.g. every second of a 1Hz sine wave), you'll find that its always at the same point in its period. Phase shifting, well, shifts this point depending on the symbols you want to send.
In reality, modulation techniques are much more complicated, often it's not just 1s and 0s but tons of different symbols that can be sent, sometimes with a combination of modulations. For example, if you combine AM and FM you could say a quiet, lower frequency is 00, a quiet higher frequency is 01, a loud lower frequency is 10 and a loud higher frequency is 11. There's infinite ways for this, what matters is that sender and receiver speak the same modulation.
Sending data over sound is the very same principle, your carrier signal is an audible tone at some frequency and everything else is modulated onto it with some technique.
Sound is just changing amplitude of pressure in the air. If there are repeating peaks and valleys in that amplitude of pressure within the human audibility range (Roughly 20Hz to 20,000 Hz) the human brain perceives those repeating peaks as valleys as sound.
If you take any electronic signal that has peaks and valleys in that range and apply it to some kind of speaker (like even just a paper cone being driven by an electromagnet directly connected to that electronic signal), you’re converting those electronic peaks and valleys into peaks and valleys of air pressure, which a listener would hear as sound.
If you're old enough, you may remember the modem screech from the 90s or the cellphone interference noise from the 00s. That's digital transmission being converted into sound, in the latter case inadvertently.