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I don't understand converters

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Re: I don't understand converters

PostPosted: Sun Sep 22, 2019 10:09 am
by Hugh Robjohns
The Elf wrote:Generally speaking, balanced gives more signal for less noise. If you have the option to use a balanced connection, use it.

Cue a clutch of 'ah, but...' responses! ;)

The 'ah but' is only because the noise benefit depends on the exact balanced output topology being employed... but in general you're right to say that there can be a 3dB benefit in the signal-noise ratio.

The way it works is this: assuming the balanced output is the symmetrical/inverted type, where the two legs carry coherent, same amplitude, signals but in opposite polarities, then the addition of those two signals at the balanced differential receiver produces an output which is double the amplitude of either leg individually -- meaning the output is 6dB greater.

However, the noise contribution from the output driving electronics being conveyed over each leg is not coherent, so its addition at the receiver results in a 3dB rise in the noise amplitude.

Thus, the wanted signal is 6dB greater but the noise is only 3dB larger, and so there is 3dB more signal than noise overall... as per the Elf's statement above!

As I said, though, there are caveats because this benefit is not available from all forms of balanced source configurations.

And for me, this very modest improvement in S-N ratio is generally irrelevant anyway because the noise floor of decent electronics is so low that 3dB really doesn't make any audible difference in the vast majority of applications. What really does make a big difference, however, is the avoidance of ground-loops and the minimisation of external interference -- and that's why I always use balanced connections whenever they are available!

H

Re: I don't understand converters

PostPosted: Sun Sep 22, 2019 11:05 am
by The Elf
Ah, but... my version was shorter! :lol: ;)

Re: I don't understand converters

PostPosted: Sun Sep 22, 2019 11:50 am
by Hugh Robjohns
it always is! :D

Re: I don't understand converters

PostPosted: Sun Sep 22, 2019 12:14 pm
by Wonks
Indeed. Elf's version of John Cage's 4'33" is only 2'05".

Re: I don't understand converters

PostPosted: Sun Sep 22, 2019 12:14 pm
by Hugh Robjohns
:lol: :clap:

Re: I don't understand converters

PostPosted: Sun Sep 22, 2019 12:31 pm
by Sam Spoons
Wonks wrote:Indeed. Elf's version of John Cage's 4'33" is only 2'05".

If he played it to an empty theatre would is actually have happened?

Re: I don't understand converters

PostPosted: Sun Sep 22, 2019 1:30 pm
by Wonks
Sam Spoons wrote:
Wonks wrote:Indeed. Elf's version of John Cage's 4'33" is only 2'05".

If he played it to an empty theatre would is actually have happened?


I think I'll give that question the short silence it deserves. :D

Re: I don't understand converters

PostPosted: Sun Sep 22, 2019 2:08 pm
by Tim Gillett
The Elf wrote:
Because he can hear, or thinks he can hear, audible benefits
I'd reduce that to 'thinks he can hear, or is financially advantaged to say he hears...' ;)

Cynical? Moi? :beamup:

On another recording forum I once frequented, were a number of posters whose argument was "I know what my ears tell me" and that was always the end of the discussion...especially if they were not prepared to subject their claim to double blind testing, which, it was sometimes claimed, was just a conspiracy to trick them...

Re: I don't understand converters

PostPosted: Sun Sep 22, 2019 2:11 pm
by ManFromGlass
Wonks wrote:Indeed. Elf's version of John Cage's 4'33" is only 2'05".

Is Elf running at 30 ips in a 15 ips world?

Re: I don't understand converters

PostPosted: Sun Sep 22, 2019 2:33 pm
by Wonks
ManFromGlass wrote:
Wonks wrote:Indeed. Elf's version of John Cage's 4'33" is only 2'05".

Is Elf running at 30 ips in a 15 ips world?

Maybe. I've been told by others that he has ultrasonic hearing and speech and at times only converses with the genus Chiroptera. In other words, he's completely batty. :D

Re: I don't understand converters

PostPosted: Sun Sep 22, 2019 6:30 pm
by blinddrew
It occurs to me that I have probably had my set up backwards. I've had my CD and MD players running into my Dacmagic, and then the unbalanced audio running into my Focusrite Scarlett and on to my speakers.
In retrospect I should probably be taking the digital out from my focusrite into the dacmagic and the balanced audio output from that to my speakers. Just need to check that I can still control the volume via the focus rite.
Oh yes, and buy some female XLR plugs and solder them up.
Which probably means getting the dacmagic fixed so that all the inputs work as well. :(

Re: I don't understand converters

PostPosted: Mon Sep 23, 2019 12:38 pm
by CS70
songwriter wrote:I need to understand once and for all about converters.
...
So I am more confused now than before. This engineer mixes and matches converters?? Why? What's the difference in sound and why would it have an effect on program material?

This is actually easier than it looks.

A converter has a job - polling your analog signal with a given frequency to transform it into a stream of samples with the desired word length.

If it were possible to build a perfect real-world converter, it would do that job and that one would be all that you even needed.

But it isn't. Real-world converters are less than perfect.

So different converters (based on different classes of tech or different designs in the same class) produce slight different errors. The sample streams they produce are (often very, very slightly) different.

That results into slightly different analog signal when the samples are used to reconstruct the (supposedly) original waveform. Aka "different sound".

Errors can come from timing (frequency must be ultra precise), how the gain-to-digital level is interpreted (ideally should be a straight line, but physical components may not behave so) and so on. Also boundary conditions like operating temperature (often linked to the voltage) can affect the signal detection and different designs will attempt to compensate for these physical effects in different ways (usually the better they are, the more costly, with the inevitable law of diminishing returns creeping in).

Keep in mind these effects are really minimal - for example, the time scale with which music is understandable to us (say milliseconds for a note) is way bigger than the time scale with which a converter operates (even a humble 44.1Hz is 44100 times per second, an order of magnitude greater).

Nevertheless: these errors all result is slightly different (but musically equivalent) sample streams and reconstructed-analog-wave.

Some people claim to be able to hear the differences. How much that claim is true or self delusion, it's hard to say - nobody's ever organized a proper blind test insofar I know.

One funny thing to think about, is that the same micro-errors are sure to occur (for the same physical-vs-theoretical reasons) in D/A conversion.

So, are these fellows hearing the A/D conversion errors, or the D/A conversion errors? A mix? :-) Who knows. My $.10 is that we people are great at fooling ourselves, especially when we've used a hefty dosh of cash on something. But your opinion may differ.

Beyond that, exactly like you can't evaluate a microphone unless your room is pretty good (a fantastic mic will capture fantastically a horrible comb-filtered signal, if the room is very reflective, resulting in a horrible recording), evaluating a converter without having a really great chain before is nonsensical.

Maybe, maybe, if you have a great room, a really good fidelity microphone, a great (low distortion, low noise, as-linear-as-possible) preamp... you can hear what the converters errors do. Maybe. Dunno. I don't.

I also understood that the converter acts as the audio interface, like the fireface UFX. Is that right? Or can you have a different converters like the ones above integrated into your normal recording setup (in my case with the UFX) to change at will?

No - "interface" stands for "computer interface": that is, an interface is what takes the samples from the converter to the PC (via USB, thunderbolt etc). A stand alone converter usually doesn't "talk" these computer protocols, so usually need to take the (already digital) sample stream and send it into an interface. which then converts them to USB etc.

That's due (my guess!) to historical reasons, with protocols to transmit audio signals (like AES/EBU or S/PDIF) having evolved in parallel with device-to-computer communication protocols (like USB), and from slightly different viewpoints.

Bit like Nikon and Canon being both cameras, but needing adapters to use each other's lenses. Or Apple and PCs being both computers but.. you get the gist.

On the other side, all interfaces that expose analog inputs (line or mic) contain A/D converters. There are interfaces which are digital to digital (to translate between the various digital audio protocols, say AES to MADI etc) and then get the signal into a computer. These won't contain converters, but are far fewer and normally oriented to the pro market rather than the consumer.

Due to the theory-vs-real-world-effect above, at a given price point a design that deals only with conversion (i.e. an A/D box) vs. one that has to deal with preamp + conversion + translation to computer protocol (i.e. an interface) will likely do a slightly worse job at A/D. But in reality really good A/D conversion chips, supporting reasonably good analog front-ends, have become commonplace so it's not really something you should concerns yourself unless you can (as opposite to want) squeeze the last 0.0001% of performance from your chain.

Like it's not a big deal - for the purpose of driving fast - to worry about the micro-meter smoothness of a cars paint coat if you don't have a great pilot, engine, suspensions, injection, reliability etc..

Shameless plug: if you like, you can always have a look at my blog http://theaudioblog.org where I write about these things.

Hope it helps!

Re: I don't understand converters

PostPosted: Mon Sep 23, 2019 1:08 pm
by Mixedup
Hugh Robjohns wrote:What really does make a big difference, however, is the avoidance of ground-loops...

And since we're on the subject of converters... this is one reason I like optical digital connections such as ADAT and optical MADI.

Re: I don't understand converters

PostPosted: Mon Sep 23, 2019 2:42 pm
by Hugh Robjohns
Mixedup wrote:And since we're on the subject of converters... this is one reason I like optical digital connections such as ADAT and optical MADI.

But only if you use those high-quality fibres with the gold-plated connectors, yes? :lol: :lolno:

Re: I don't understand converters

PostPosted: Tue Sep 24, 2019 6:07 pm
by blinddrew
Hugh Robjohns wrote:
blinddrew wrote:Is there any technical advantage to using the balanced outputs on the dacmagic over the unbalanced ones?

It should also provide at least a 3dB improvement in the signal-to-noise ratio compared to the unbalanced outputs. I've not run a suite of measurements on my original DACMagic converter box (but I will now I'e reminded myself that I should)... but reviews I've seen suggest the balanced outputs have something like 2dB lower distortion products than the unbalanced outputs.

H
Just wondering if you had time to run those measurements?