How does sound recording and playback work?

Question

An ipod plays music, but is there a little band in there?

Answer 1

No it is a digital recording, a compressed one at that with only the sounds that you can hear.

Sounds can be expressed on a graph as a sine wave; a wave the goes up and down, up and down. The distance between the up and down points and the height and depth of the waves determine the sound. When we record that sound we are making a copy of those peaks and valleys, on an axis of time; which then lets us reproduce those sounds. What you end up with is a series of positive and negative numbers that are played at a specific speed. Now computers love to process numbers and do a very good job of it. All that is needed is a set of good speaker or ear buds to reproduce those sounds.

The technology is a little more complex in real life because you have to try and get the tone of each instrument and voice which calls for some extra data to be included (or encoded) and some extra processing on the part of the machine. Otherwise it would sound plinky; like computer music used to sound.

Next the file is compressed to save space, all the highs and lows you can't hear are removed and the time scale is shrunk to make a smaller file. The iPod or MP3 players knows exactly how the file is changed because of the way that it is encoded and what the last three letters on the file name are; those letters tell the computer what type of coding is used.

When you download the songs into your iPod or MP3 player you are sending the compressed file to RAM; random access memory. A magnetic field in a computer chip is flipped to on or off in a combination of this is called binary, language which is what all computers use. You can store the normal numbers we know of in binary; they are just longer and require a conversion routine. This is all real simple for a computer to do.

So inside of your iPod or MP3 player is a tiny computer that only handles music, a series of memory chips that hold the songs, the processing equipment to turn the numerical signals into sounds and the power source. This is why we can get it so small. Cell phones are similar is some respects and we can get them much smaller.

In the next generation of players like the video iPod or the Zune there is a TV screen made out of LCDs which is included. This too is a digital signal and recorded and processed the same way the signal is for sound only it is much more complex. Since the processor is very specialized and dedicated we can make it smaller. The Apple iPhone is just a cell phone + an iPod + a video player. All of it is specialized and uses similar processing techniques. The information is stored on a magnetic chip so keep your iPod away from magnets and you old cathode ray TV tube has a big one inside of it.

That is the basics of an iPod. It includes a sound synthesizer to produce the sound. Back when Steven Hawking first needed a computerized voice the sound synthesizers were pretty primitive. When we got the software and computer hardware designed properly that opened the door to creating iPods and MP3 players. The only way to improve the technology is to shrink it even more and to add more memory so you can store more songs, and to add other functions like receiving wireless signals.

With your iPod player Apple encodes a special computer signal inside of the song; signals that you can’t hear, these signals store your user name and the fact that you paid for the song so the iPod can play it. MP3 files can store this data, but most people don’t add it, this is why they can be traded freely. Your iPod songs include antipiracy software to prevent them from being used by other people illegally. The Microsoft Zune uses something similar. Because you have to buy the music the music industry likes players like iPod and Zune, but not the standard MP3 player.

An older method of music encoding (MP2) is used to play your CDs, and that came from an improvement over the old analog method of recording it on magnetic tapes or in a wax disk that was played on a phonograph record.