Back to basics. Definition: Analogue audio

[Ken Tajalli]

Recent replies on "Is Digital Audio Transmission Analog?" has shone a light on the (mis)definition of Analog audio.
Many have sort of asserted that since there are conductors and an electrical current flowing through it, then it is analog!
See these examples:
- “Digital” is a mathematical representation. Signal transfer is through voltage and voltage is an analog quantity. Digital signal representation is transferred by means of analog quantity - voltage.
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- Digital is nothing more than a useful technique, or like *** said, a mathematical representation. Even the data storage on our computers is just different levels of stored electrons on memory cells. Theoretically everything in life is analog. Isn't it beautiful?
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- No. The first thing you learn in Digital Design 101 (actually 2-something) is that digital is just a special case of analog.
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Without a solid, unified definition, we can not go forward in a scientific discussion.
I think it is time to have a bullet-proof definition for Analogue signal in general and Analogue audio in particular.
Ofcourse we could do a little Google and come up with some, but what do you think?
Afterwards, we could have a bullet-proof definition of Digital signal and digital audio in particular.
But for now, let us talk about Analogue Audio only.
It may sound mundane, but it seems we need to define certain phrases before we use them.

Any takers?

 

[fpitas]

A signal is "digital" because it has been " sliced" at a pre-determined voltage level. For example, the peak-peak may be 3.3V, going from 0 up to 3.3V; but at 2V (for example) you decide it is indeed a 1. Below 2V it's a 0. Yes, there's more to it than that, but that's the concept.

 

[Ken Tajalli]

A signal is "digital" because it has been " sliced" at a pre-determined voltage level. For example, the peak-peak may be 3.3V, going from 0 up to 3.3V; but at 2V (for example) you decide it is indeed a 1. Below 2V it's a 0. Yes, there's more to it than that, but that's the concept.

Thank you for replying.
But the question for now is Analog signal, once we covered this, we can move forward to Digital and then to comparison.

 

[JSmith]

I think it is time to have a bullet-proof definition for Analogue signal in general and Analogue audio in particular.

Huh?

In a nutshell, PWM is a way of digitally encoding analog signal levels. Through the use of high-resolution counters, the duty cycle of a square wave is modulated to encode a specific analog signal level. The PWM signal is still digital because, at any given instant of time, the full DC supply is either fully on or fully off. The voltage or current source is supplied to the analog load by means of a repeating series of on and off pulses. The on-time is the time during which the DC supply is applied to the load, and the off-time is the period during which that supply is switched off. Given a sufficient bandwidth, any analog value can be encoded with PWM.

Introduction to Pulse Width Modulation - Embedded.com

A look at a powerful technique for controlling analog circuits with a microprocessor's digital outputs. Pulse width modulation (PWM) is a powerful

www.embedded.com

JSmith

 

[Ken Tajalli]

Huh?

Introduction to Pulse Width Modulation - Embedded.com

A look at a powerful technique for controlling analog circuits with a microprocessor's digital outputs. Pulse width modulation (PWM) is a powerful

www.embedded.com

JSmith

Thank you too, but not knowing what Analogue Audio is, in the first place, a certain type of digital encoding technique is beyond the scope of this thread.

 

[fpitas]

At the risk of being obvious, analog audio is what's left when no digitization techniques are used.

 

[RayDunzl]

Analog:

It's waves, all the way down..

Sound? Waves

Storage? Waves

Transmission? Waves

Reproduction? Waves

 

[FrantzM]

I'll take a stab at it. I will not try to pedantic but this may be more complex (pun intended) than one would think.
An electrical signal has usually a modulus (voltage, amperage) and a frequency... It is what is called in mathematics a complex number.
Complex numbers are of the form:

The "i" is defined as:

In a complex number (a signal can be represented by complex numbers). "a" and "b" are real numbers.. that is any number between - infinity and + infinity... Take any number 1,9874566666 or Pi (π) =3.1415926535 8979323846 2643383279 5028841971 6939937510 5820974944 5923078164 0628620899 8628034825 3421170679 ... that its value to 20 decimal places... or anything in between or outside ...


In an analogue signal, a and b can take any value in the real number space ... even if you limit the values of a and b to be between -2 and +2 ... i-e in maths terms -2=<a<=2 and ... "a" and/or " b can take ANY, value in between... 1.094765974 or 1.985546548468484884 or -1.93584848484894848452487... etc...

In a digital signal. You limit the value that can be taken by "a" and "b". They only take what is called "discrete" steps. usually 2 to the power of something... that is 2 x 2 x 2 ..etc thus for 4 bits, "a" or "b" can only take strict values in 16 steps..., equally spaced steps.... of 0.25... thus you would have: The only value that can be taken by "a" and "b" would be:

-2, -1.75, -1.50, -1.25, -1.00, -.75, -.50, -.25, 0, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50, 1.75, 2... "a" and "b" shall only take one of those values.. Nothing in between ...
Digital signal aka discrete signal....

Peace.

 

[digitalfrost]

I think with regards to audio it is rather simple: If there's quantization, it's digital.

 

[Ken Tajalli]

In an analogue signal, a and b can take any value in the real number space ... even if you limit the values of a and b to be between -2 and +2 ... i-e in maths terms -2=<a<=2 and ... "a" and/or " b can take ANY, value in between... 1.094765974 or 1.985546548468484884 or -1.93584848484894848452487... etc...

I can agree and see some truth in that, though it is not a definition, but it hints at the underlying notion of analogue signal as having ANY value between a set range, so is not limited to any predefined level-steps.

In a digital signal. You limit the value that can be taken by "a" and "b". They only take what is called "discrete" steps. usually 2 to the power of something... that is 2 x 2 x 2 ..etc thus for 8 bits, "a" or "b" can only take strict values in 16 steps..., equally spaced steps.... of 0.25... thus you would have: The only value that can be taken by "a" and "b" would be:

This again is a comparison of Digital to Analogue, which I hope would come after. Basically what you re saying is that digital audio are snap-shots of the value against a stepped value table at certain times, much akin to Cinema! where stationary pictures are taken at certain time intervals.

Peace.

Peace? you're gonna start a war.
Do you agree with my deductions?

 

[FrantzM]

I believe you understood ... That is what it was all about..

I can agree and see some truth in that, though it is not a definition, but it hints at the underlying notion of analogue signal as having ANY value between a set range, so is not limited to any predefined level-steps.

This again is a comparison of Digital to Analogue, which I hope would come after. Basically what you re saying is that digital audio are snap-shots of the value against a stepped value table at certain times, much akin to Cinema! where stationary pictures are taken at certain time intervals.

Peace? you're gonna start a war.
Do you agree with my deductions?

As for the "Peace" sign-off... We need peace. Our tendency toward aggression is not serving us all...


Peace

 

[DonH56]

For N bits the number of values is 2^N, so for 8 bits you actually have 256 values. The number of steps is one less, e.g. 255 for 8 bits, since you do not include the "ground floor" (the range of values for an unsigned 8-bit converter is 0 to 255).

The definitions that I and others have used for decades:

• Analog = continuous in time and amplitude
• Sampled-analog = discrete time or amplitude, other parameter continuous
• Digital = discrete in time and amplitude

Loosely, analog is a continuously-varying signal without discrete time or amplitude (voltage, current, power, displacement, whatever) values. Digital is numerical with values quantized in amplitude and time (thus chosen from a fixed, discrete set of values). Sampled-analog applies to things like a sample-and-hold (or track-and-hold) that quantizes in time but not in amplitude. Bucket-brigade delay lines and CCD imagers are sampled in time but not in amplitude. The delay line's output is usually applied to an analog amplifier, essentially staying sampled-analog in nature, whilst an imager's cells usually feed an ADC and so are quantized (digital) after conversion. A basic comparator without a latch (i.e. no clock) will quantize in amplitude but not in time -- it flips whenever the signal crosses a threshold.

These are pretty fundamental definitions used by standards bodies like the IEEE, at least when I was involved with such things.

FWIWFM - Don

 

[Salida]

The simplest definition I can think of:
Analog audio is continuous over time and amplitude.

Digital audio is both sampled and quantized, so no longer continuous with respect to time and amplitude.

Test one: Is a sampled signal analog? No, it is not continuous over time.
Test two: Is a quantized signal analog? No, it is not continuous over a range of amplitudes.

Test three: What happens at the limit? As sampling frequency increases and the number of quantization steps increases then a sampled and quantized (digital) signal approaches, but never reaches, becoming analog again. Of course this is a theoretical construct and the practical matter is different in that if your quantization step size is smaller that the Brownian motion of the atoms comprising the noise floor of your system, it probably doesn’t matter. /)

 

[maverickronin]

Somehow this hasn't been brought up either here or in the other thread, but it's analog which just the approximation.

The universe is quantized all the way down - matter, energy, time, and space.

It's just that usually the individual quanta are so small compared to the scale one is working at that it's easier to treat values as continuous.

 

[fpitas]

Somehow this hasn't been brought up either here or in the other thread, but it's analog which just the approximation.

The universe is quantized all the way down - matter, energy, time, and space.

It's just that usually the individual quanta are so small compared to the scale one is working at that it's easier to treat values as continuous.

Right? But maybe true audiophiles can hear the quantitization noise of the universe. That would explain why we don't understand them

 

[danadam]

The universe is quantized all the way down - matter, energy, time, and space.

The next question is, what's the bitdepth of the universe

 

[DonH56]

I figured someone would bring quantum mechanics into it. I almost did myself but why... Consider my definitions "macro" if you please.

Aleph-null, aleph-one, hmmm...

If you filter quantum noise with a flux capacitor, is it analog?

 

[fpitas]

The only thing you can do for quantum noise is use a quantum purifier. Good thing we have those now. What an age we live in!

 

[Ken Tajalli]

The definitions that I and others have used for decades:

• Analog = continuous in time and amplitude

So would you call DC an analogue signal, it is a continuous voltage and in time does not change.I have to ask to get a clearer answer.
After all, I am after bullet-proof Def. Think of it as not coming up with a good description, but something like a legal contract! That leaves no room for misinterpretations or abuse!

Loosely, analog is a continuously-varying signal without discrete time or amplitude (voltage, current, power, displacement, whatever) values.

So Analogue is not restricted in time or amplitude, unless one sets a range.? do you agree

Digital is numerical with values quantized in amplitude and time (thus chosen from a fixed, discrete set of values). Sampled-analog applies to things like a sample-and-hold (or track-and-hold) that quantizes in time but not in amplitude. Bucket-brigade delay lines and CCD imagers are sampled in time but not in amplitude. The delay line's output is usually applied to an analog amplifier, essentially staying sampled-analog in nature, whilst an imager's cells usually feed an ADC and so are quantized (digital) after conversion. A basic comparator without a latch (i.e. no clock) will quantize in amplitude but not in time -- it flips whenever the signal crosses a threshold.

I intend to cover Analogue first - though it is proving difficult!
It is like saying, what is white, and the answer comes coloured is this and that, so what is not coloured is white!

These are pretty fundamental definitions used by standards bodies like the IEEE, at least when I was involved with such things.

Thank you, I am aware that there are set-in-stone definitions at IEE or IEEE, but there are some members here who are not engineers and they have loosely collected understanding on analogue signal.

 

[JSmith]

The universe is quantized all the way down - matter, energy, time, and space.

It's certainly a possibility and quite an interesting topic in itself. Something I have been looking into in more depth recently too.

What is the Planck time?

The almost impossibly brief Planck time has been known since the 19th century. Originally dismissed as a mere curiosity, it may hold the key to understanding the universe.

www.space.com

One possibility is that spacetime itself is quantized at the level of a Planck length and Planck time. If this is true, then the fabric of spacetime, when looked at on that scale, would appear “chunky” rather than smoothly continuous.

Is space-time smooth or chunky?

A new study tried to find out.

www.space.com

One of these videos was about it, but I can't recall the title/subject heading;

https://www.youtube.com/c/pbsspacetime/videos

JSmith