# Why are cassette tapes considered analogue? [closed]

As far as I can tell, the cassette ribbon can only have the magnetic particles arranged in 2 directions, making it digital. So why are they called analogue? Is this a sort of gray area?

• can it? have you told magnitism that – JonRB Jun 17 '17 at 18:39
• individual film grains can be clear or opaque, and light at some level is quantum, yet we still refer to film photography as analog because it's not discrete. Thus, even if tapes were only N+S at full Gauss, unless we counted each "magnet" we cannot 100% reproduce the signal since the audio would be an averaging of the indeterminate poles. – dandavis Jun 17 '17 at 20:33

Magnetism is traditionally referred to as having North and South polarisation (two directions). Magnetism however is a vector which has direction and magnitude.

One area could be perfectly aligned with "N" and say 1mT, another could be perfectly aligned with 0.5mT.

Likewise the field could be aligned +45deg from N

By varying the field intensity when the magnetic tape is recorded, the magnitude of the analogue data can be superimposed

http://hyperphysics.phy-astr.gsu.edu/hbase/Audio/bias.html#c4

• No need to be crusty, there are plenty of digital magnetic devices, and I thought this was one of them. Here's a good visualization of the non- digital nature of cassettes. reel2reeltexas.com/vinAd49MakingMagRecVisable.jpg – noobboob Jun 17 '17 at 19:19
• I wasn't being crusty oO I just stated magnetism is a vector and thus analogue information can be stored – JonRB Jun 17 '17 at 19:20
• No, this graphic post was good, but your other comment was dumb. Thanks for the answer btw. – noobboob Jun 17 '17 at 19:29
• @noobboob Why so rude? – pericynthion Jun 17 '17 at 22:25

The fact that magnetic particles have only two possible orientations (which is essentially false in the first place) make magnetism as much digital as electrons, which have only two possible spins (if my memory serves me right).

Joke aside, what makes magnetism analogue is that the stored information is a linear — as opposed to digitized — response, in the mathematical sense of the term, to the input signal. A digital signal is quantized first using an analogue-to-digital conversion, which causes its digital representation to fit a finite amount of states (e.g. $2^{16}$ or $2^{24}$), as opposed to a (theoretically maybe) infinite number of states for analogue systems. As a result, digitized signals are non linear representations of the initial signal. For example, current, also, may have only two (symbolic) polarities (plus or minus) but it can vary linearly in amplitude between two given values, whereas if it were digital it could only vary in steps.

Think of analogue as a linear representation and digital as non-linear. This is my non-scientific definition of the differences between analogue and digital.

• There are plenty of digital magnetic storage devices, I assumed audio cassettes were one of them. – noobboob Jun 17 '17 at 20:13
• Well, usage is one thing. The fact that tapes can be used to store digital information doesn't mean they digitize the information they store. – user59864 Jun 17 '17 at 20:28
• Wouldn't that make everything stored as analogue? A CD would be analogue because the pits aren't exactly the same size, but it meets the logical threshold and becomes digital. – noobboob Jun 17 '17 at 21:14
• I think you are mixing up some different ideas: An analog signal is represented by some physical variable (current, voltage, frequency,...). A sampled signal has a value that only changes at regular, discrete instants in time. A quantized signal has only a finite number of possible values. A signal can be sampled and quantized and still be analog; OR, it can be encoded as a sequence of numbers, and thereby become a digital signal. I won't say what linear means 'cause I'm not a mathematician, and I'm not sure I would get it right. – Solomon Slow Jun 17 '17 at 21:22
• @noobboob There can be many layers of meaning in a signal. All recordings are analog at the lowest level---the output from the photo diode in a CD player is a continuously varying voltage; but there are many layers of meaning. At a higher level the CD signal is interpreted as a sequence of rising and falling edges, and at a higher level still, as a sequence of bits, from which a higher level extracts frames of bytes and words. At some highest level (I don't know how many layers there really are) it is interpreted as samples in a digitized, stereo, audio stream. – Solomon Slow Jun 17 '17 at 21:37

as you said its more like in grey area. if you record an audio it will fall in to analogue because you not doing any encoding or decoding but if you use this as a digital data storage like in the late 1970s audio cassettes are used as digital data storage1.

wikipedia ref.

how audio recording is done

• Thanks, I know magnetic storage CAN be used for digital data, but I was mistaken to think the audio cassettes used that method. – noobboob Jun 17 '17 at 19:26