Would this improve the quality of signal to a CNC machine?

Bit of a sting there James however it's read.

Emgee

Any time varying current is analog. I suppose you would agree that a sine wave is an analog signal. Well a pulse train is a series of sine waves of different frequencies. Do the Fourier transform. For USB the data is encoded and decoded as digital on the analog carrier as I said which is what makes it a digital communications channel but the connection is analog. It is splitting hairs but that's the way it is.

regards Martin

A digital signal is an analogue signal with only two or three levels. That is why it is called a digital signal. (Yes, if zero is a level, and it is, then digital signals can have three levels, but they are still digital signals.)

I must have skipped that class. You're not the first new member to wade in guns blazing and telling people that they're idiots and I don't suppose you'll be the last. Generally it reflects badly on the new poster and while some quieten down many disappear without trace.

As a doctor I'd advise you to visit your GP, as breathing cutting oil fumes seems to have affected some cognitive abilities.

Andrew

Precisely, which is why I asked about FSK, as in it's simplest form it consists of bursts of two sine waves, but is considered as being a digital signal.

The definitions of digital signals above are fine as far as they go, but are limited. The question of noise is an interesting one, first analysed by Shannon and Hartley. But consider a GPS signal which can be at least an order of magnitude below the background noise level, but can still be decoded. Speaking of decoding, a comparator deciding whether a signal is high or low is an example of hard decision decoding. Newer algorithms, such as Viterbi decoders, use soft decision decoding based on the reliability of each code. Logic levels at the gate level are normally described as above a given level is 1 and below another given level is 0. Zero is normally included in the lower range rather than as a discrete logic value. The precise voltage is unimportant provided it is above, or below, the specified levels. There is normally a voltage range between the levels where the signal is neither 1 nor 0. Of course more than two levels can be used, although the only common example is a third state of high impedance aka tri-state logic.

Andrew

A well designed cable and made with reasonable quality materials does not cost very much. It is unlikely to be the cheapest you can find but it will be very affordable. Many data systems can correct errors or retry so poor performance can be compensated for, only when performance drops to a very low level will failure be signaled. Design is the first hurdle because poor design cannot be compensated for by using high quality materials but a good design can be ruined with poor materials or workmanship.

Mike

Or RS-232.

Martin Kyte wrote:

" Any time varying current is analog. I suppose you would agree that a sine wave is an analog signal. Well a pulse train is a series of sine waves of different frequencies. Do the Fourier transform. For USB the data is encoded and decoded as digital on the analog carrier as I said which is what makes it a digital communications channel but the connection is analog. It is splitting hairs but that's the way it is."

That's more sensible and describes the mechanism - but actually supports the necessary differentiation between the digital and analogue. It really is not splitting hairs as an appreciation of the difference between signal, channel, carrier and their 'layering' is essential to any understanding of digital (or any other form of) communications.

I apologise if I may have overreacted to seeing incorrect statements regarding digital signals but teaching digcomms to half a generation of undergraduates (most of whom have achieved good degrees and gone on to successful careers in R&D and industry) has made me particularly sensitive to any misconceptions of this sort.

No, they are intended for digital use, Ian really has linked to a three and a half grand USB cable.

Take a look at some of the utterly mind bending drivel in the second of his links, my favourite bit was this " This innovative layout allows the two signal wires to run parallel, compared to the standard twisted-pair configuration, shortening the signal path and drastically increasing transfer speeds"

The thing I really don't understand about audiophiles is why none of them have twigged onto the most obvious way of improving the sound experience, that being reception fidelity interoception. The simple and straightforward application of a pair of underpants to the head supplemented with correct tuned length wood and graphite frequency modifiers in the nasal cavity can take the listening experience from the sublime to the ridiculous in one fell swoop.

I will put my hands up and admit that I am a hi-fi fan. My investment in Hi-Fi way exceeds the value of my workshop.

That said the digital part of the system uses standard Ethernet patch leads costing a few pounds. The argument used for the esoteric USB and network cables is reducing the noise transmission from the digital to analogue domain rather than the quality of the signal itself. I don't buy it and I agree that there is a lot of snake oil in the industry. None of purchases have been made without auditioning first.

The comments about made about no difference between bell wire and a quality speaker cable clearly come from those who have never heard the latter. I will happily admit to spending £40/m on cables and it was the best investment I made, with a dramatic improvement.

I have had friends round (before lockdown) who like music but don't have a quality playback system and they have been blown away by the sound quality.

Maybe the poster was being just a little flippant but using thicker low-loss cables than thin bell wire can improve the listening experience. Paying £40/m is your choice and if you like the result, that's fine you can spend your cash on what you like without comment from me. Similarly, I can have an opinion for me, and for me, I think it is very poor value for money - and yes, I have tested it all out.

I think some might interpret this as willy-waving.

Difficult - I think Mr. Edmund Blackadder has the patent.

Just going back to the original (tongue in cheek) question, I think it's rare for CNC machines to use USB to carry any signals - there are USB connected motion controllers but it seems to be generally reckoned that Ethernet is better. Lathe does have a USB connection from the PC to the breakout board but it is entirely to supply +5V and carries no data. There are high-speed pulse signals from the controller to the steppers but they are at 40 volt 2.5 amp levels.

Now then, let's not have pistols at dawn over the difference between Analogue and Digital Signals! This is a jokey thread about highly dubious USB cables, not an advanced class in telecommunications theory.

I know what James meant, and I know what Andrew meant and feel the difference is semantic. A slight twist in what's understood by 'analogue' has led to unecessary trouble at t-mill.

For what it's worth (not much!), I suggest a digital signal is a digitally modulated analogue carrier. The carrier, another word we could start a row about, could be light, radio waves, or on/off keying of a DC voltage. In my book good old Audio Shift Frequency Keyed radioteletype once ubiquitous on short-wave radio is a digital signal, but it's sent by alternating two audio tones and applying them to modulate an RF carrier, also analogue. The receiver is analogue up to the point the two tones are converted into binary HIGH/LOW, at which point the signal is pure digital.

I'd be amazed if anyone disagreed that the charactistic of analogue modulation is information represented by continually varying values, whereas digital is information represented by a stream of HIGH/LOW transitions, however HIGH and LOW are defined.

Dave

That's interesting. At which university did you teach?

Andrew

Prepare to be amazed! What about Gaussian pulse shaping? Analogue filter theory used to shape a digital pulse stream.

Another topic to mull over is QAM - quadrature amplitude modulation. It's amplitude modulation but mostly used for digital information, eg, digital terrestial TV in the UK. Each symbol can have many levels, so more than 1 bit can be transmitted in one symbol, 64 and 256 are common values, as the constellation is normally square. Where's the dividing line between continuous modulation and modulation of many discrete steps?

Andrew

Andrew: Cambridge.

SillyOldDuffer:

" I think some might interpret this as willy-waving."

Well, I've had more graceful responses to an apology

The Interweb is packed with nonsense, advice and 'howtos' posted by idiots who have no idea of which they speak so in my experience it's always a very good idea to check provenance before accepting anything too readily. I merely pointed out that I do actually know what I'm talking about - why should you apparently have some sort of problem with that?

When were you there? I was at CUED from 1980 to 1986, but don't recall your name.

Andrew

I'd be more amazed if anybody on this forum ever agreed with anybody else!

But I am constantly amazed at the breadth and depth of knowledge on this forum.