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Is Digital Audio Transmission Analog? [video]

DonR

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Is that something he does with the homeless?
0PfMfYb.gif
 

RayDunzl

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You might not use 1 million sine waves, but the frequency content must be there to look "square'ish".

I could only find about 1,100 discrete frequencies in the 10Hz square I measured, of course I was bandlimited...

index.php
 

fpitas

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I could only find about 1,100 discrete frequencies in the 10Hz square I measured, of course I was bandlimited...

index.php
Sure but digital data rates are up to 100Hz now!
 

Cbdb2

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Yeah, digital audio is transferred by voltage swings if you use a coaxial connection. USB probably works differently (but in the end its still based voltage changes). Optical has no voltage swing of course.

I'm pretty sure Darko understands this, but he is just peddling nonsense because that can make him more money.
Theres a dozen ways to modulate a digital signal for transmission, voltage swings is one.


The most common, Ethernet, uses PAM. https://www.edn.com/pam-ethernet-a-perfect-match/

Which gets me thinking, why don't we use Ethernet for home audio? Its huge in the pro world.

Cables connectors and hubs are cheap and reliable and devices can be 300' apart.
 

pma

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You might not use 1 million sine waves, but the frequency content must be there to look "square'ish"
Again, I would respectfully disagree. I do not need the “squareish” look only, I need rise time and fall time of the square wave shorter than 10ns. 10ns rise time is 35MHz corner frequency, 1ns means 350MHz. Why? Because square is to investigate stability. And you may get into troubles even at frequencies between 10 MHz (power amp) to 300MHz (preamp with diamond buffer). Again, I speak based on real circuits, real experience, not just to debate. And for the same reason I am not much interested in a school type lecturing debate.
 

pma

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I could only find about 1,100 discrete frequencies in the 10Hz square I measured, of course I was bandlimited...

index.php
Yes but I want rise time 10ns and shorter. 35MHz BW at least. Squares generated by any audio DAC are good for fun only. They are useless for stability investigation. This is the key, you guys only think in low frequency perspective, thus talking about synthesis of a square from sines and created by audio DAC. You need fast impulse generator, not the DAC.
 

DonDish

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I am not sure what this means. A "digital" signal is a sequence of bits (bitstream) that could in general be any pattern, e.g. 10101... or 100011011111000111... or whatever. Most high-speed serial interfaces recover the clock from the data stream, obviating the need for a separate clock line and attendant need to synchronize clock and data lines. Many standards (SAS, SATA, PCIe, etc.) encode the bitstream to prevent long runs of 1's or 0's that can cause the clock recovery circuit to lose lock (get out of synch with the signal) -- a PLL needs frequent transitions (edges) to phase-lock to the signal. There is not a carrier in the sense of an RF modulated signal that mixes LO (carrier) and IF/baseband signals to produce an RF output (or vice versa in the receiver).


How to make a square wave: https://www.audiosciencereview.com/.../composition-of-a-square-wave-important.1921/


AES or S/PDIF, as well as the aforementioned protocols, send a bitstream using a reference clock for Tx and the receiver recovers the clock from the signal. I2C and I2S are example of protocols that have an explicit, separate clock line.

FWIWFM - Don
I guess I got my kick in the nuts afterall. What I was trying to explain was PCM but its hard when I started out with a stupid asumption which fucked it all up. I will shut my mouth and go back to school about this. :D
 

DonH56

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Again, I would respectfully disagree. I do not need the “squareish” look only, I need rise time and fall time of the square wave shorter than 10ns. 10ns rise time is 35MHz corner frequency, 1ns means 350MHz. Why? Because square is to investigate stability. And you may get into troubles even at frequencies between 10 MHz (power amp) to 300MHz (preamp with diamond buffer). Again, I speak based on real circuits, real experience, not just to debate. And for the same reason I am not much interested in a school type lecturing debate.
That is not in disagreement with the composition of a square wave, e.g. the frequency bandwidth (content) needed to provide the desired risetime. And my data (measured, not just theoretical) showed signal content commensurate with the risetime as one might expect. Limiting the bandwidth leads to things like the Gibbs Effect, which is a real-world, measurable, observable phenomenon. I do in fact have real-world experience with real circuits, including the square-wave generator I built and mentioned that had ps edges, but this is going nowhere and is off-topic so I'll drop it.
 
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DonH56

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I guess I got my kick in the nuts afterall. What I was trying to explain was PCM but its hard when I started out with a stupid asumption which fucked it all up. I will shut my mouth and go back to school about this. :D
Ah, I suspected as much after rereading your post. Carry on. I've already been accused of being a schoolboy lecturer without real-world experience so I think I'd best stay out of this thread. I'm busy testing some 32 Gb/s devices and trying to explain to a customer why adding a couple feet of cable thoroughly mucks up a 22.5 Gb/s signal that is supposed to be measured at the pins of the device. Sometimes I wish I was back in school. :)
 

DonDish

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Ah, I suspected as much after rereading your post. Carry on. I've already been accused of being a schoolboy lecturer without real-world experience so I think I'd best stay out of this thread. I'm busy testing some 32 Gb/s devices and trying to explain to a customer why adding a couple feet of cable thoroughly mucks up a 22.5 Gb/s signal that is supposed to be measured at the pins of the device. Sometimes I wish I was back in school. :)
Lol. Good luck with that! IT pays good I bet, you have to comfort yourself with that when they make you do stuff. Dream about the hifi stuff u could buy
 

DonH56

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Lol. Good luck with that! IT pays good I bet, you have to comfort yourself with that when they make you do stuff. Dream about the hifi stuff u could buy
Not in IT, analog circuit design and test, don't get me started on our IT department's imaginative means of blocking productivity ("takes a computer")...

At this point I have more than enough hifi stuff, but of course that does not stop the dreaming. :)
 

VonGoethe

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HI,

I've been dealing with the topic "Ethernet sound" for a long time now and have also made various measurements of switches and cables:
This link is with Google translate - may contain wrong translations.

The only way that Ethernet becomes sonic is through common mode noise, which is either produced by the switches and network interfaces, or is converted from differential to common mode on the signal path through mode conversion. This noise is also proven to be passed from the streamer to the DAC via USB.
There is also a thesis that jitter establishes itself as interference in the ground system in the lower frequency range and can thus have an effect on the sound, but so far without measurable evidence.
 
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Ken Tajalli

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The link was specifically about the "Composition of a Square Wave". If you have a better explanation of square wave composition than the sum of odd harmonics, I'm all ears ;)
Of course, I am not as knowledgeable, but isn't Fourier analysis just a mathematical dissection of a square wave into virtual sine waves of odd harmonics?
A square wave is a square wave, as he correctly states:

1669979556033.png

A square wave is not composed of anything but DC that switches on or off, of course one can create a facsimile of a square wave using sine waves, but just because a piece of glass can be shattered into millions of smaller triangular or otherwise pieces, the reverse is not true!
i.e. , claiming the glass was originally compromised of those smaller pieces.
The act of shattering the glass creates the smaller pieces, just a filtering a square wave, creates the sine waves!
I state that @pma is spot-on about square waves, if one wants to imagine a square wave as an infinite number of sine waves, as a means or aid of calculations, they may do so, but a square wave is composed of nothing but DC getting switched off and on FAST!
 
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pma

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if one wants to imagine a square wave as an infinite number of sine waves, as a means or aid of calculations, they may do so, but a square wave is composed of nothing but DC getting switched off and on FAST!
Exactly! For the testing purposes that needed shortest impulse edges, we used avalanche transistors to switch (short) DC via a resistor and got a sub-nanosecond edge. For testing high current shunts, mercury wet realy was used to do a similar job.
 

Plcamp

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I ran an engineering and compliance certification team at a major telecom company, which included EMI, RFI and Signal Integrity engineering for very high speed core and peripheral equipment.

In that role, there’s no such thing as a digital signal…it’s high speed analogue.

In fact, one of the most significant and frequently analyzed changes we would make to emerging designs was to add limiting resistors onto data lines with excessively fast risetime, so that the unnecessary highest order harmonics of the “digital” signal don’t bounce back and forth such that a zero or one cannot be reliably detected.

So in my space, it is just analogue.
 

pkane

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Of course, I am not as knowledgeable, but isn't Fourier analysis just a mathematical dissection of a square wave into virtual sine waves of odd harmonics?
A square wave is a square wave, as he correctly states:

View attachment 247279
A square wave is not composed of anything but DC that switches on or off, of course one can create a facsimile of a square wave using sine waves, but just because a piece of glass can be shattered into millions of smaller triangular or otherwise pieces, the reverse is not true!
i.e. , claiming the glass was originally compromised of those smaller pieces.
The act of shattering the glass creates the smaller pieces, just a filtering a square wave, creates the sine waves!
I state that @pma is spot-on about square waves, if one wants to imagine a square wave as an infinite number of sine waves, as a means or aid of calculations, they may do so, but a square wave is composed of nothing but DC getting switched off and on FAST!

Mathematics is like that: if you have two equivalent representations of the same signal, these representations are both valid and can be used interchangeably. Neither one is "the one correct" representation. Just because DC switching is easier to understand and use in practice, doesn't make the Fourier representation any less valid.
 

Ken Tajalli

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I ran an engineering and compliance certification team at a major telecom company, which included EMI, RFI and Signal Integrity engineering for very high speed core and peripheral equipment.
In that role, there’s no such thing as a digital signal…it’s high speed analogue.
In fact, one of the most significant and frequently analyzed changes we would make to emerging designs was to add limiting resistors onto data lines with excessively fast risetime, so that the unnecessary highest order harmonics of the “digital” signal don’t bounce back and forth such that a zero or one cannot be reliably detected.
So in my space, it is just analogue.
Isn't it a question of Horses for courses ?
Under certain applications (i.e. long cabling, Telecom, very high data rates etc. ..) it is practical to think of everything as analogue as anything that can cause a problem in an analogue domain, can and will have an impact on digital transmission too.
But narrowing it down to a short USB or SPDIF cable, or anything that maybe used in a Hifi environment, then those analogue problems become insignificant, and one can treat the transmission as Digital.
Of course, if the cable being used happens to be so bad and substandard that the problems become noticeable, it should not be an excuse to say transmission was analogue.
 

Ken Tajalli

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Mathematics is like that: if you have two equivalent representations of the same signal, these representations are both valid and can be used interchangeably. Neither one is "the one correct" representation. Just because DC switching is easier to understand and use in practice, doesn't make the Fourier representation any less valid.
Aha!
But isn't Fourier analysis an approximation? After all, sine wave components approximate a square wave, but never actually make it.
Staying with mathematics, a perfect square wave does exist, but a composition of sine waves keeps getting closer and closer to a perfect square wave, and indeed one needs an infinite number of them.
Using switches (transistor, relays or even a push button) to create a square wave, one starts with DC , where are the sine wave components?
There aren't any!
Now if you filter that, you create the sine waves, just like my glass example.
 

Plcamp

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Isn't it a question of Horses for courses ?
Under certain applications (i.e. long cabling, Telecom, very high data rates etc. ..) it is practical to think of everything as analogue as anything that can cause a problem in an analogue domain, can and will have an impact on digital transmission too.
But narrowing it down to a short USB or SPDIF cable, or anything that maybe used in a Hifi environment, then those analogue problems become insignificant, and one can treat the transmission as Digital.
Of course, if the cable being used happens to be so bad and substandard that the problems become noticeable, it should not be an excuse to say transmission was analogue.
It depends on speed, and the basic principle is that where possible you should limit the bandwidth of the signal you send so that the ability of the far end receiver to detect a valid one or zero is maximized. That essentially means you don’t want to send a mathematically perfect square wave, because that would degrade that ability of the far end to detect

So yes you are correct, in instances where the sent digital signal has a very wide detection window (slow data rate) you need not worry yourself. The effects I speak of by sending faster harmonics than you need affects the one to zero and zero to one waveshapes at the transitions…which are only a minor % of the signal when it is slow.
 

Plcamp

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Aha!
But isn't Fourier analysis an approximation? After all, sine wave components approximate a square wave, but never actually make it.
Staying with mathematics, a perfect square wave does exist, but a composition of sine waves keeps getting closer and closer to a perfect square wave, and indeed one needs an infinite number of them.
Using switches (transistor, relays or even a push button) to create a square wave, one starts with DC , where are the sine wave components?
There aren't any!
Now if you filter that, you create the sine waves, just like my glass example.
Well, here is a question that might help.

Imagine you have a high voltage capacitor and say it is charged to 1500v.

40 feet across the room you have a high speed analogue spectrum analyzer looking for signals only in the 1MHz to 10MHz range through a filtered antenna.

Now you suddenly discharge that dc charged capacitor directly to ground…bang!

Do you expect the spectrum analyzer would detect nothing? If it does detect something, the presence of sine waves can’t be denied, can it?
 
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