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HighFidelityGuy
22-04-2009, 13:53
Hi,

I've always thought that electrical digital interfaces like SPDIF should give better sound quality than optical. This is because with optical the signal is changed from electrical to light and back the electrical again, instead of just staying electrical all the time.

What are peoples thoughts on this here? Do you think there is much of a sound quality difference between the two?

The reason I'm wondering is that I may need to swap from using SPDIF to optical soon between my PC and DAC.

Thanks.

Spectral Morn
22-04-2009, 14:31
Hi as long as both digital interfaces have been designed and implemented well and poorness in one or the other does not bias the question one way or the other; I have always found co-ax hook up to sound better than optical (though optical can be better over very long distances). To my ear and with the kit I have used optical has always sounded a bit softer and more rounded. Co-ax more open and detailed.

For not a lot of doe the Qed SR75 cable is very good...I use these in my AV set up and in lesser digital connections, opting for much more expensive elsewhere such as XLO and PAD cables.



Regards D S D L

Sand Dancin Donkey Walker
22-04-2009, 14:38
Hi Guys

On my DAC I have the option of either Co-Ax, Toslink Optical or the AT&T Optical. Never liked the Toslink, but currently use the AT&T.

Now this subject has been brought up again, I will have to re-visit the options and see what I think now. Will report back my findings.

Andy - SDDW

lovejoy
22-04-2009, 14:39
Well, this is purely my experience and I tend to trust my ears rather than try to think of the why's or the technicalities of these things because you end up going mad, but I've found that the cable is more important than the transmission method. I've heard good and bad in both optical and coax.

I always favoured coax when used between DVD players or CD players and amps, but I think there's a good argument for using optical when using a computer just to give you complete electrical isolation from all of the electrical noise that a PC generates.

When I bought my Beresford DAC, I bought one of Stan's optical cables, then later found my old IXOS optical cable I thought I'd lost. I was glad to have bought Stan's cable after comparing the two as if I'd used the IXOS from day one, I'd probably never thought much of Stan's DAC. The IXOS cable made everything bright and hard to the point of being unlistenable. I'd have never attributed such differences to optical cables.

HighFidelityGuy
22-04-2009, 15:12
Thanks for the info. Perhaps swapping to optical won't be the end of the world then. :lol:

The reason I may need to change cable types is that I'm thinking about getting a Behringer DEQ2496 to go between my PC and DAC to allow me to try out room correction. The DEQ2496 has AES/EBU and optical inputs and outputs. According to Behringer the AES/EBU connections can be set to use SPDIF signals but that still leaves me the problem of converting the connection type from XLR to phono. I'm a bit wary of this due to the different impedances etc and the expense of getting decent cables made to suit. So using optical would probably be cheaper and simpler.

Does anyone have any experience with connecting AES/EBU equipment to SPDIF equipment?

Thanks.

Spectral Morn
22-04-2009, 15:27
Cheap plastic optical cables are crap....good glass ones are better. The AT&T connection is a very good option but is only found on American gear normally such as Wadia (its a communications industry/telecoms pro option) It is very good and can be better than the other connection types.

Quality of cables does make a difference. My answer was based on the very best being used in either type plus the connections on the gear being equally the best, and my preference is for co-ax...95% of the time with the other 5% being AES or AT&T, depending on the kit. My preference so far has never been for optical connection.

In the context of PC/Mac optical or USB may be better...as I have no experience of either I am not sure.....


Regards D S D L

Ali Tait
22-04-2009, 19:14
From what I've heard,both options are pretty dire.Friends who know a lot more than me have implemented I2S connections with transformers in their DIY DAC's and to my ears it's far superior.

tizer2000uk
22-04-2009, 20:58
In my experience I have found that as long as the cheap n cheerful cables are not used the difference between them is minimal at best.

jonners
22-04-2009, 22:18
Does anyone have any experience with connecting AES/EBU equipment to SPDIF equipment?



I've used the DEQ2496 and had no problems matching it to SPDIF dacs. I made up the cable myself though.

But if you're using a PC as a source, surely there would be some software available that would do the room correction? That way you would avoid having another box, more cables etc. This is not an area I know much about, but I bet someone on A of S could advise.

ReachtheSky
23-04-2009, 02:49
I sometimes use the DEQ2496's partner, the SRC2496, and have had no problems matching it to SPDIF sources. In fact, one of the strengths of these DEQ2496/SRC2496 products is their versatility and connectivity.

ReachtheSky
23-04-2009, 02:51
John, how did you go with your DEQ2496?

I’ve been considering trying the DEQ2496 for room correction also. I’ve read a few reports where users have suggested “room correction” has made a more significant improvement than any other “tweak” and at good value for money.

Comments such as “......using the DEQ to optimise the speaker performance, the sound in my listening room is beautifully balanced. And if you don't have your speakers' performance optimised for your room, you're, IMHO, wasting a LOT of money. And the DEQ does this beautifully, regardless of price.”

Cheers Granville

maxrob200
23-04-2009, 04:50
In my system I find there is a huge difference between co-ax and toslink. For co-ax I use 1.5metre of Belden 1694A 75-ohm cable. Toslink is one that was purchased from an electronics part shop.
The co-ax is smoother, richer and more open and revealing.Toslink sounded squashed and thin by comparison. I read somewhere that the optical transmitters and receivers have very low bandwidth and compared to AT&T is poor in perofmance

jonners
23-04-2009, 07:50
John, how did you go with your DEQ2496?



Hi Granville,

The benefit of the DEQ2496 is of course very room- and speaker-dependent. After a lot of fiddling I stopped using the 'Auto Correction' and just used it to cut the bass frequencies where the room was booming. I liked it and found it pretty transparent. For what it offers it's a very good deal.

Since changing to open baffle speakers I haven't felt the need for it so much, as OB's tend to interact with the room rather less.

gary_j
23-04-2009, 09:42
Hi, was going to start my own thread but here seems a good place to ask :)
Im trying to decide whether to use Optical or Coaxial for my system.
It will be connecting my PC to a beresford 7250.
It needs to be fairly long, around 8-10 metres.
Anyone know what the maximum lengths are for each cable?
I always seem to here that Coaxial sounds "better" but Optical will obviously be better shielded from interference from my PC etc.
What cable do you think would be best?

Cheers, Gareth

HighFidelityGuy
23-04-2009, 09:42
Thanks for all the input guy's. :)

John, would you be able to tell me how you wired the XLR end of your custom cables please?

I did wonder about getting some RTA software for my PC but the problem with this is that I'd also need a proper balanced Mic input on the PC too with phantom power etc so that will complicate things in other ways. I can also see this method working out more expensive.

jonners
23-04-2009, 13:59
Thanks for all the input guy's. :)

John, would you be able to tell me how you wired the XLR end of your custom cables please?



Earth: Join pins 1 and 3. Signal: Pin 2.

HighFidelityGuy
23-04-2009, 14:08
Earth: Join pins 1 and 3. Signal: Pin 2.

Excellent, thanks.

What XLR connectors did you use?

jonners
23-04-2009, 14:53
What XLR connectors did you use?

I used Neutrik digital, but I don't think it makes much odds what you use.

HighFidelityGuy
23-04-2009, 15:24
I used Neutrik digital, but I don't think it makes much odds what you use.

Thanks. I guess they'll be the XCC series. They took a bit of finding on the Neutrik site. The price seems quite reasonable so I think I might give the SPDIF route a try. I've emailed Mark Grant a couple of times asking if he can make up some cables for me but I've not had a reply. I might just order the right length SPDIF cables from him and fit the XLR's my self for the quickest.

ReachtheSky
23-04-2009, 21:19
Hi HighFidelityGuy,

I’m really interested to see how you go with the DEQ2496 for room correction and any other tweaks you use it for (apparently it has Swiss Army knife type multifunctional). It’s also exceptional value compared to TacT or other such product!

Regarding connectivity with these Behringer products, I have used the SRC2496 as a DAC but more importantly as a means to eliminate jitter and reclock digital signals from inexpensive transport sources, and have had no connection problems.

I use cheap XLR to RCA adaptors where required and they work very well. I’m able to mix between XLR, RCA and optical without issues and the SRC2496 automatically recognises the input. Some use it for this purpose only.

The only problem can be the high (pro) output to analogue for professional equipment. On the SRC it is about double gain. The DEQ has a (internal) switch to adjust this output gain for either pro output or something similar to normal HiFi gain output.

Regards Granville

ReachtheSky
23-04-2009, 22:13
Gareth, I’ll be interested to hear how you manage to connect your PC to 7520 over 8-10m with Optical or Coaxial.
I suspect you may have to go USB or streaming (i.e. Squeezebox) for that distance.

For 10m USB you would need a 5m plus 5m repeater (amp) USB cable. But I don’t know the audio quality of such an arrangement. Can anyone comment on the audio quality on different USB cables and lengths. I presume better shielding would give a cleaner less jitter signal? I’d appreciate any comments here!

When all else fails….SB3 or SBDuet to the rescue!
Granville

NRG
24-04-2009, 06:41
The AES3 format was designed to be used up to 100M distance, however, SPDIF using good coaxial cable runs to 10-15M max. Toslink is really limited to under 10M, so I'd go coaxial and use double shielded 75R cable.

Quietschbox
24-04-2009, 07:37
Did anyone mention cable length yet? I read something about signal echoes in short cables (for electrical spdif connections). Something like 1,5 metres minimum length needed to avoid echoes.

And regarding optical - it's impossible for most users to actually measure jitter, but the conversions on the optical links needed are said to create serious timing/jittter problems. More than the electrical version, and in effect the verdict is that the optical transfer usually is inferior to the electrical link.
So, maybe, although the thread starter opted for, you shouldn't discuss sound impression first, but second, and technology&jitter first?

Or rather lookup "s/pdif" "jitter" "optical" .

Did that, found
"Even modern DACs have typically a small buffer and reclocking circuitry, so the jitter is not so big problem nowadays that it used to be."

So it totally depends on your devices and cables used.

HighFidelityGuy
24-04-2009, 08:15
Thanks everyone, there's some really interesting info here. :)

USB cables are limited to about 4-5M length without using an active extension or a USB over CAT5 adapter kit, but I doubt that will be good for audio. So it sounds like good quality SPDIF coax is the best option for runs over about 4-5M. I currently have a 4M Mark Grant SPDIF cable between my PC and DAC and it works really well.

I too have read that SPDIF cables shorter than about 1.5M are bad due to internal reflections. Also the cable, the terminations, the output socket and the input socket all need to be the correct impedance. I read that many cheap devices aren't designed correctly and don't have the correct impedance. Also many SPDIF cables apparently just use standard analogue phono plugs instead of proper 75Ohm ones.

I'm definitely going to try the coax route with the DEQ2496 first, now that I know it can work well. It'll probably be a couple of months until I get a DEQ though as I want to upgrade some other parts of my system first.

I'm also going to experiment with DIY room treatment before I try the room correction as I think will be the best order to do things in. I want to try and get to a point where I only have to use the DEQ for subtle EQ tweaking as I believe EQ should be used as sparingly as possible.

maxrob200
24-04-2009, 10:59
A number of posts on the net recommended 1.5 m of co-ax cable to minimise reflections. The exact explanation is uncertain to me. Perhaps someone on the forum can explain this further. The suggested cable is Belden 1694A solid core 75-ohm cable, which I believe is used by several companies for digital cables

HighFidelityGuy
24-04-2009, 12:02
The Mark Grant SPDIF cables are made with Belden 1694A.

NRG
24-04-2009, 12:21
I can't right now think of a reason why a USB to ethernet converter would be bad for sound quality. If such a setup works for file data then it sure will work for audio.

The use of RCA with SPDIF means the connector are not impedance matched, the recommendation for 1.5m cables seems to work but it does not stop signal reflections just alters the reflection timing. The best idea is to use BNC but its not easy to retro fit them if you are no good at DIY.

There are RCA to BNC converters available but I can't vouch for their effectvness.

maxrob200
24-04-2009, 22:15
Yes, I do believe that BNC are best. The problem is that most Transports (SB3 etc) and DACs are not fitted with BNC. I wonder how much compromise in sound quality there will be in using RCA compared to BNC. Has anyone done a comparison of the same cable terminated with either RCA or BNC and come to some form of conclusion?

foxysounds
25-04-2009, 18:50
Well, last night I did a head to head comparison of optical vs coax digital and I can't tell the difference.

I had both optical and coax connections from my CD6000OSE into my new Beresford TC-7520 and when changing the selected input on the DAC I could hear no difference at all.

The optical cable I used is made by QED but I'm afraid I have no idea what the model number is. I don't even remember buying it :scratch:

The coax cable is a Belden 1694A cable courtesy of Mark Grant Cables.

Simon.

Tony Moore
26-04-2009, 13:26
I remember doing a similar comparison with my SB3 -> TC7510 into WAD HD83 and Beyer DT990 headphones. I could certainly tell a difference between them. It wasn't huge but it was there. I preferred the sound via the electrical interface, however that doesn't mean it was better, just that it was different and I preferred it. That also could be down to my optical i/c quality vs the electrica i/c quality.

Headphones are _very_ revealing, I doubt I'd be able to hear the same differences through speakers.

Cheers,
Tony

Quietschbox
26-04-2009, 15:02
Headphones are _very_ revealing, I doubt I'd be able to hear the same differences through speakers.


Place both speakers left n right to your ears and you will hear way more detail.:eyebrows:
Don't forget to keep the kids away from the amp.

Quietschbox
26-04-2009, 15:10
Empirical Audio Pace-Car Reclocker
http://forums.slimdevices.com/showthread.php?t=37557

Quotes, in order of pages:

"The point of this reclocker [pace car] is the same as everything else sold by Empirical Audio:
to part credulous audiophiles from their money (in large chunks preferably)."

"One man posted in a tread in another forum. He worked in a studio. Dont remember where or when. His statement of claim was that jitter dos not exsist.
It is something the pro audio hardware industry has invented to earn more money on hardware sales."

"Once you have heard the SB3 with the Pace-Car at 16/44.1, you wont care about 48kHz. Its that good.
Steve N.
Empirical Audio"

"I've been modding DAC's for many years, and I've probably modded 15 different ones.
I found that none of them are immune to jitter, even though most have some claims of such.
Steve N.
Empirical Audio"

Internet threads about usefulness or uselessness of expensive equipment can be entertaining.

Chippy_boy
22-08-2009, 15:07
Or rather lookup "s/pdif" "jitter" "optical" .

Did that, found
"Even modern DACs have typically a small buffer and reclocking circuitry, so the jitter is not so big problem nowadays that it used to be."

So it totally depends on your devices and cables used.

How true. A decent modern dac is much more tolerant of a jittery signal than earlier ones. That being the case, optical should be able to sound just as good as coax. There's only bits and jitter in the signal - nothing else. Get the bits right and remove the jitter and there's nothing else left to make them sound any different... apart from the snake oil.

Tom472
25-08-2009, 12:09
Some manufacturers are now offering the at&t standard optical interface (much better than TOSLINK, designed to take the kind of banwidth required by digital audio).

This has received some good write up on the DIYaudio forum as a DIY option too. This would presumably be the best option for a long cable run between source and DAC.

The internal reflection issue with short co-ax cables stems from the whole 75 ohm issue. There shouldn't be any reflections if the cable, connectors, transmitter and receiver circuitry are all proper 75 ohm items. As some have noted, phono plugs rarely are.

I bought some BNC sockets a while ago which seem to fit perfectly into the hole left by commonly used phono sockets - its an easy DIY switch.

Regards
Tom

StanleyB
25-08-2009, 12:40
Some manufacturers are now offering the at&t standard optical interface (much better than TOSLINK, designed to take the kind of banwidth required by digital audio).
What's the bandwidth of digital audio, and what's the bandwidth of TOSLINK?

DSJR
25-08-2009, 13:35
In decades past, the Toslink connection was judged inferior due to the loose mechanics of the system I believe. the AT&T connectors were judged far superior back then.

Never having carried out measurements or any research on this, I'm just repeating "feelings" by those who were supposed to know.

Barry
25-08-2009, 15:16
Some manufacturers are now offering the at&t standard optical interface (much better than TOSLINK, designed to take the kind of banwidth required by digital audio).

This has received some good write up on the DIYaudio forum as a DIY option too. This would presumably be the best option for a long cable run between source and DAC.

The internal reflection issue with short co-ax cables stems from the whole 75 ohm issue. There shouldn't be any reflections if the cable, connectors, transmitter and receiver circuitry are all proper 75 ohm items. As some have noted, phono plugs rarely are.

I bought some BNC sockets a while ago which seem to fit perfectly into the hole left by commonly used phono sockets - its an easy DIY switch.

Regards
Tom

Given the dimensions of an RCA phono connector, it can never have a 75 ohm impedance.

BNCs are obtainable in two versions: 50 ohm and 75 ohm. Make sure yours are 75 ohm and remember that a 50 ohm BNC plug has a centre pin of larger diameter, so will physically damage a 75 ohm socket if it is mated with one.

Regards

Tom472
26-08-2009, 08:57
What's the bandwidth of digital audio, and what's the bandwidth of TOSLINK?

It's a bit difficult to say as its not a constant signal in the normal analogue sense and also varies depending on the data being sent. Most people specify standard 16 bit stereo to be around 6MHz, some would say its technically much higher than that.

As for the bandwidth of TOSLINK, well it depends on what it's made of, how good the interconnects are etc. Poor cables (the plain clear plastic ones) will do about 5MHz, better cable should get to more like 10MHz. The interface between the light source and cable is also pretty critical, and this is generally where a lot of TOSLINK interfaces cause problems. Optical connections obviously have the potential for very high bandwith, as demonstrated by high speed phone lines etc.

Having said all that though, as noted earlier, as long as the signal is effectively re-clocked at the other end, the bandwith limitations shouldn't technically contribute to "jitter".

Regards
Tom

StanleyB
26-08-2009, 10:02
Most people specify standard 16 bit stereo to be around 6MHz, some would say its technically much higher than that.

As for the bandwidth of TOSLINK, well it depends on what it's made of, how good the interconnects are etc. Poor cables (the plain clear plastic ones) will do about 5MHz, better cable should get to more like 10MHz.
For Gigabyte transmission, fiber optic cable require a far wider bandwidth. In the case of 5.1 and 7.1 audio, the bandwidth is also far higher than for 2 channel stereo.

The reason I asked the question is because there are TOTX and TORX sockets designed for high frequency applications that are in excess of the 2 channel stereo spec., as well as fiber optic cables to support high bandwidth applications.

I am not sure what type of fiber optic cabling AT&T uses, but I have been using high bandwidth optical cable in the design of my own TOSLINK cables, and high bandwidth TORX sockets on my DACs for years without any hoohaa being made about it.

The following is a pic of a standard audio TOSLINK cable, next to one of my high bandwidth fiber optic cable terminated into TOSLINK connectors.

http://www.beresford.me/images/leads/T2M.jpg