ELIF: How are audio and video stored on CDs and tapes?
In: Technology
Audio is the most straightforward to explain: The microphone picks up sound in waves which can be “described” digitally. The computer or recording device takes in the sound wave and produces a corresponding output of 1s and 0s.
Those specifically arranged 1s and 0s are sent to the CD burner (for example) which uses a laser to either activate or not activate individual spots on the CD which correlate to whether that spot should receive a 1 or a 0.
So now you have a CD with a grid, more or less, of tiny spots, some “on” and some “off”
When you place that CD into a CD player, the player reads which bits of the CD are on or off, turns that back into 1s and 0s which it can then turn back into information that it can send to speakers to produce the same sound waves that were recorded originally.
Things get a little different for video/tape. I’ll leave that for someone else as I cannot confidently explain it in a way that would be appropriate for this sub.
The two are very different technologies.
CD which stands for compact disc. It stores the information in the form of digital infirmation that is burned onto the surface of the disc. The burning of information onto the disc is done using light which heats up the disc and rearranges the chemical composition of the disc’s surface to remember the information that we’re trying to store.
To replay the information that has been put onto a disc a light is shined onto the disc while it spins to replay what’s been stored on it.
Tape on the other hand, uses a magnetic technology to arrange the data on the reel of the tape. Unlike the CD technology, magnetic tape uses the same magnetic head to both record and replay the data.
On CDs and DVDs there are little bumps (burns) in the reflective surface in a spiral shape. When the laser from a disc reader “reads” the disk, it’s capturing either a reflection (0) or a hole (1) which is binary for the machine reading it. The computer then converts the binary to a digital signal.
On tapes, magnetic tape is passed through a series of magnets which record whatever you want onto the tape. When you put it through another magnetic reader, the change in fields on magnetic tape are converted to an analog signal.
Edit: analog
The CD/tape does not actually contain the sound/image stored on it. It contains math that tells the device you’re reading it with how to make those sounds/images.
It’s basically a recipe your device reads to make it’s own audio and video just like the ones the person who recorded the recipe made.
* CDs.
* To start with CDs are digital by nature, so they store data using a binary encoding.
* The simply means each value in the system is either in one state or the other.
* For CD’s there are little holes in the CD material that a laser can read.
* The holes are mapped to either one state of the other and the data is mapped to that.
* Tapes
* Magnetic tape uses the strength of the magnetic field stored in the tape to represent information.
* ***It can be either analog or digital.***
* In digital, just like the CD, the magnetic field is either strong or weak. The strong and weak sections are mapped to one state or the other and now we have the same kind of data stream as the CD.
* However tape can also use an analog encoding scheme where the intensity of the magnetic field maps to some varying signal.
* This works great for audio because audio can be easier captured as a varying voltage and that varying voltage can be easily converted back to physical sound waves.
* On a tape, the varying strength of the magnetic field can easily be converted into a varying voltage which as we just stated can easily be turned into a physical sound wave.
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