Digital to coaxial

[Dwaindibly]

Hi can anyone explain what does the job of converting a digital signal in order for it to be sent via a coaxial cable or and optical cable? I know one is electrical and one uses light but what hardware actually does the job is it something like a dac chip ?

 

[voodooless]

It’s a chip called SPDIF transmitter. It usually inputs i2S and outputs an SPDIF signal that can then be transferred via coaxial, or can be converted to light via an optical transmitter (basically a LED). In some cases the transmitter chip is integrated into a larger SOC (system on a chip).

The transmitter muxes clock and data lines into the SPDIF encoded signal, see:

S/PDIF - Wikipedia

en.m.wikipedia.org

 

[Berwhale]

Hi can anyone explain what does the job of converting a digital signal in order for it to be sent via a coaxial cable or and optical cable? I know one is electrical and one uses light but what hardware actually does the job is it something like a dac chip ?

An SPDIF transceiver will be used to convert the I2S signal from the source into an AES3 signal which then be transmitted over co-axial cable or converted to light to send over an optical link.

Nice pictures from TI...

DIX9211 data sheet, product information and support | TI.com

TI’s DIX9211 is a 216kHz Digital Audio Interface Transceiver (DIX). Find parameters, ordering and quality information

www.ti.com

 

[Dwaindibly]

So the SPDIF signal goes straight to the coaxial output were optical is converted to light then output ? and can the quality etc of these components affect sound quality ?

 

[Berwhale]

So the SPDIF signal goes straight to the coaxial output were optical is converted to light then output ? and can the quality etc of these components affect sound quality ?

I think there will probably be some sort of amplification of the electrical AES3 signal before it goes over the co-ax, but that is probably part of the chip. The optical signal needs a transducer to convert the electronic signal into light (photonic signal). If all this is done without altering any of the bits in the digital signal (which it will be, unless it's broken), then there is no impact on the digital signal and there can be no impact on the 'sound quality'.

Have a read of this: https://en.wikipedia.org/wiki/Shannon–Weaver_model

 

[RayDunzl]

Is the one on the right dead?

 

[Dumdum]

Is the one on the right dead?

Just drunk… but not legless!

 

[wwenze]

SPDIF digital data to SPDIF PHY is very straightforward... in many cases e.g. old computers, cheap audio equipment the coaxial doesn't even follow SPDIF spec...

This will give an idea of how simple it is

 

[Dwaindibly]

That's great thank you for explaining it I'm just trying to understand why some prefer coaxial over optical and how one could be better than the other and vice versa when it's all noughts and ones

 

[MAB]

That's great thank you for explaining it I'm just trying to understand why some prefer coaxial over optical and how one could be better than the other and vice versa when it's all noughts and ones

If you listen without knowing the connection type and without peeking, you will never be able to tell the difference.

Unless you have a ground loop that the optical solves. Or compare the two between different DACs not level matched, or different filters, or one of the DACs is junk.

Some people believe they hear differences between optical and coax with everything else matched. They actually can’t and fail to identify the differences in a proper test where they are not allowed to see which connection is being used.

It is after all data. And audio is on the extremely easy side of data I/O.

 

[Berwhale]

That's great thank you for explaining it I'm just trying to understand why some prefer coaxial over optical and how one could be better than the other and vice versa when it's all noughts and ones

I think the only reason I would choose optical over a co-axial connection would be to electrically isolate the components to prevent a ground loop. Otherwise they are equivalent to each other.

 

[somebodyelse]

Is the one on the right dead?

It's certainly the right way up for 'dead bug prototyping'

 

[AnalogSteph]

I think the only reason I would choose optical over a co-axial connection would be to electrically isolate the components to prevent a ground loop. Otherwise they are equivalent to each other.

Toslink receivers can have marginal / insufficient bandwidth for 192 kHz, so that's something to keep in mind.

 

[Dwaindibly]

Looking at specs for different optical cable manufacturers only say they support up to 198khz so are most cables running at maximum capacity? and can spdif output higher rates ?
And I haven't found a manufacturer that gives specs for max bitrate for coaxial

 

[voodooless]

Looking at specs for different optical cable manufacturers only say they support up to 198khz so are most cables running at maximum capacity? and can spdif output higher rates ?

SPDIF supports a max sample rate of 24-bit 192 kHz stereo sampling. Over coax or AES, this is trivial. As mentioned already, many optical transmitters stop at 96 kHz, but some also support up to 192 kHz. This is mainly due to the simple construction of those transmitter blocks and the use of super cheap LEDs. They simply do not have a fast enough rise time to keep up. So a more expensive model can reach those speeds. Next, as a medium, simple plastic tubing is used to transport the light. This is very far removed from a fiber optic network connection that uses glass fibers to transport multi-10-gbps.

And I haven't found a manufacturer that gives specs for max bitrate for coaxial

It is usually in the specs of the devices.

 

[Randyman...]

ADAT Optical does over 12Mbit/s, but not the same format and baud rates as consumer SPDIF.

 

[antcollinet]

That's great thank you for explaining it I'm just trying to understand why some prefer coaxial over optical and how one could be better than the other and vice versa when it's all noughts and ones

I've no idea why some prefer coaxial, probably, in most cases, some factually incorrect audiophile folklore they've read in the past that convinces them it is "better".

I have a preference for optical, because it also has inherent galvanic isolation which can break ground loops.

 

[voodooless]

ADAT Optical does over 12Mbit/s, but not the same format and baud rates as consumer SPDIF.

That's similar to 24-bit, 192 kHz stereo, so ADAT gives you 8 channels of 24-bit, 48 kHz. Similar number of bits

 

[somebodyelse]

I've no idea why some prefer coaxial, probably, in most cases, some factually incorrect audiophile folklore they've read in the past that convinces them it is "better".

I have a preference for optical, because it also has inherent galvanic isolation which can break ground loops.

Folklore had it that jitter was worse on toslink. The sample rate limitation may have come into it too.

Coaxial may have galvanic isolation too. Transformer isolation of the transmitter is required in the AES/EBU spec, so pro gear will have it. Domestic gear might, but you will probably have to test it to find out. If they can put one in a <€20 Fun Generation USB interface the cost really shouldn't be an excuse.

 

[voodooless]

Transformer isolation of the transmitter is required in the AES/EBU spec, so pro gear will have it.

There is no such requirement as far as I know. You can also get by with special line drivers that offer transformer-live floating outputs, like, for instance, from THAT (1606), but also the classic TI DRV134 or SSM2142.