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Topic: Doe analog magnetic recording ultimately break down into discrete samples? (Read 938 times) previous topic - next topic
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Doe analog magnetic recording ultimately break down into discrete samples?

I was excited to learn recently that bucket-brigade-devices(analog delay pedals, choruses, flangers, vibrato, are all based on discrete samples, are bound by nyquist, and alias/present the typical digital flaws.

My question is, does this not extend, technically, to analog tape, which is basically millions of particles carrying a charge? Would it not be simply an extremely high "sample rate" that could theoretically alias, etc

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #1
My question is, does this not extend, technically, to analog tape, which is basically millions of particles carrying a charge? Would it not be simply an extremely high "sample rate" that could theoretically alias, etc

Discrete time sampling requires that you have a sampling clock that is generating the discrete time intervals.  If you have a media that is composed of individual quantized particles, but they're not arranged into regular intervals, then you won't get aliasing.  Instead you get shot noise as the number of particles in any interval randomly varies.

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #2
My question is, does this not extend, technically, to analog tape, which is basically millions of particles carrying a charge? Would it not be simply an extremely high "sample rate" that could theoretically alias, etc

Discrete time sampling requires that you have a sampling clock that is generating the discrete time intervals.  If you have a media that is composed of individual quantized particles, but they're not arranged into regular intervals, then you won't get aliasing.  Instead you get shot noise as the number of particles in any interval randomly varies.

That generally makes sense, thank you!

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #3
Glad you got it. 

I think in retrospect a more clear way to have answered that question would be to say that aliasing is a discrete time process (time must be quantized for it to happen), whereas the media being made of discrete but random grains/particles/etc means that amplitude is quantized but time is still continuous, hence no aliasing. 

Re: Does analog magnetic recording ultimately break down into discrete samples?

Reply #4
Hmm, but isn't the time discrete (non-continuous) as well?. Ultimately there is a physical gap between one particle and the next, even if extremely small.

My understanding of your original post was that there is quantization of both, but because there's no periodicity in the tape, the distortion effects manifest themselves in analog tape as noise. Did I misunderstand?

(Also, I believe the number of particles per inch of audio tape is so high that there wouldn't be any harmonic energy at a frequency high enough that it could alias, even theoretically.

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #5
You can't read/play "one particle".      Digital and analog are different concepts.   A dozen eggs are digital.  A gallon of milk is analog.  ;)

Those bucket brigade devices are quantized in time but analog in amplitude.   Regular digital audio is quantized in both dimensions.


Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #6
Hmm, but isn't the time discrete (non-continuous) as well?. Ultimately there is a physical gap between one particle and the next, even if extremely small.

The gaps are continuously distributed because the spacing between particles can be anything.  E.g. two particles could touch, be 1 nm, 10 nm, or PI nm apart.  In a discrete time system, the units of time are fixed, equal, and not continuously distributed.  Therefore, the fact that you have discrete particles fixes amplitude but not time.   

(Also, I believe the number of particles per inch of audio tape is so high that there wouldn't be any harmonic energy at a frequency high enough that it could alias, even theoretically.

The power spectrum of shot noise is white and infinite, so it will always fill the bandwidth of any system it is connected to.

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #7
(Also, I believe the number of particles per inch of audio tape is so high that there wouldn't be any harmonic energy at a frequency high enough that it could alias, even theoretically.
To alias, the magnetic particles would have to be aligned in packets with common gaps like this:
Code: [Select]
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But they are spread irregularly over the length of the tape so that there is common gap over the complete width of the magnetic head gap. Even on a stereo compact cassette the width of one track is 0.6 mm which is plenty enough for lots of particles side by side, but with randomly distributed offset.

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #8
You can't read/play "one particle".      Digital and analog are different concepts.   A dozen eggs are digital.  A gallon of milk is analog.  ;)

Those bucket brigade devices are quantized in time but analog in amplitude.   Regular digital audio is quantized in both dimensions.


Technically each bucket contains an integer number of charges, so not analog.

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #9
You can't read/play "one particle".      Digital and analog are different concepts.   A dozen eggs are digital.  A gallon of milk is analog.  ;)

Those bucket brigade devices are quantized in time but analog in amplitude.   Regular digital audio is quantized in both dimensions.


Technically each bucket contains an integer number of charges, so not analog.

Well, it holds one electrical charge. It's not an integer like a mathematical integer.

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #10
Electrical charge is quantized. Each unit of charge is 1.6 x 10^-19 coulombs. There is no such thing as a fraction of an electrical charge.

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #11
Everything is "digital" at the atomic level but that's for philosophers.    In the practical world "Analog" has a has a real meaning to engineers, scientists, and to everybody who understands audio (and video and everything else).     We have to agree on the terminology if we are going to communicate.

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #12
The fact that charge is quantized leads to one of the main source of noise in analog circuits (especially amplifiers):  shot noise in silicon junctions.  Generally though since these systems are still continuous time, they are analog.  To be digital requires both quantized amplitude and time, whereas a system with quantized amplitude but continuous time (like an opamp or resistor) is still analog.

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #13
Without diving into quantum field theory, are these particles magnetically charged in only a binary way?
Is 24-bit/192kHz good enough for your lo-fi vinyl, or do you need 32/384?

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #14
I think each atom in a particle has only two states, but that atom can be aligned an infinite number of ways relative to the reading head.

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #15
I think each atom in a particle has only two states, but that atom can be aligned an infinite number of ways relative to the reading head.
That slams the door shut on this conversation AFAICT.
Is 24-bit/192kHz good enough for your lo-fi vinyl, or do you need 32/384?

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #16
When I posted my original question, I think I misunderstood. For some reason, my thought was that the playhead was ultimately reading one particle at a time.

But that's incorrect, right? All of the particles in a section of tape, as it moves past the playhead, sum together to create a magnetic field, which is truly continuous.

Is that correct?

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #17
The width of the tape being used is larger than any given particle of rust on it, that’s correct.

The discussion of quantum mechanics is only hand waving. In a practical sense analog tape is analog, both in amplitude and time.
Is 24-bit/192kHz good enough for your lo-fi vinyl, or do you need 32/384?

 

Re: Doe analog magnetic recording ultimately break down into discrete samples?

Reply #18
Thanks!

 
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