Topic: co2>jb3

[SparkE!]

Not sure if it helps -  but here's one inside shot...

What's the part number on that chip just to the right of R4?  Would you be willing to take a shot at the backside of the board?

(I'm headed out the door right now. I'll check back in a couple hours or so.)

[SparkE!]

Here's internal shots of the ODL-276.  By the way, I'm not terribly impressed with the workmanship on this thing.  The solder job is awful and they didn't clean the flux off when finished.  Also, there are traces that are not well adhered to the board.  I'm going to take preemptive action and solder wires in place of some of the traces before I reassemble the thing, especially the ones going to the TOSLINK ports.  Those were really loose and it would be just a matter of time before they broke from normal use.




As you can see, this is one of the designs that just uses inverters (74HC04-style) for drivers.  That type of design is usually quite reliable as long as they are assembled well.

I don't know what that chip is in the CO2 design, but that's a pulse transformer at the upper right of corkscrew's picture.  They use those transformers for compatibility with the AES-BEU signals.  It just converts the differential input signal on the RCA jack to a single ended signal.  That particular pulse transformer was designed for use specifically for use in circuits from Crystal Semiconductor that are involved with the transmission/reception of S/PDIF signals (ie. the CS8401 and CS8402, both of which have more than 8 pins - I'm not sure what that 8 pin IC is...).

[SparkE!]

Here's a shematic for the ODL-276 that I drew up today:
(Does anyone have a schematic for the CO2?)

[hexyjones]

Thanks  - I'll chime back in shortly...had a gig last night...figured it was best to disassemble gear after show...

[Brian Skalinder]

I've noticed a tendency among tapers to accept anecdotal evidence regarding equipment failures as proof of cause and effect.  Not all accidents in life involve clear cut cause and effect relationships.

True enough.  But the volume of issues with CO2 users indicates to me that trouble exists within a wide variety of gear combinations, regardless of whether or not the CO2 is the culprit.  And what amazes me is people still don't test their gear.

I've also noticed that there is a tendancy among tapers not to attempt to truly isolate the cause and effect relationships that DO exist.

And agreed again.  I just don't get why anyone would want to use a DFC and *not* test it, personally, for bit-transparency with their combination of gear.  Not necessarily to rule out the DFC as the problem, but simply to identify whether a problem exists, and if it does, then drill in to identify the source of the problem.

So, is that situation the fault of a weak optical transmitter on the CO2 or is it the result of a poorly designed optical receiver on the JB3 or is it the fault of a badly fitting optical cable or is it the fault of something else altogether?

Who knows, excellent point.  The point I'm trying to make is that it doesn't matter which device is at fault, necessarily - the problem exists with that particular combination of gear, for one reason or another.  Doesn't demonstrate cause > effect, but does suggest to me, anyway, that anyone running one (or any other DFC, for that matter) should make certain through rigorous testing that they aren't experiencing similar problems.  In the face of significant anecodotal evidence indicating bit-transparency problems with various combinations of gear - including the CO2 - I'm amazed people don't actually test their setups.  Shoot, I'd test my setup all over again if I switched from the OLD-312 to the -276!  And I did test all over again when I got my V3 optical mod, b/c even though I trust the Grace folks to do fine work, I wanted to know for myself whether the optical output mod was bit-transparent.  (It is, with my combination of gear.)

But that does not necessarily mean that someone cannot get bit perfect results with the CO2.

Yeah, fair enough, I should amend my previous statement to:

[1]  The CO2 is not bit-transparent with certain gear combinations, and the CO2 may or may not be the culprit.
or
[2]  No one has proven the CO2 bit-transparent with any combination of gear, so take your chances.

So, is anyone out there willing to work with me to investigate what are the real differences between the ODL-276 and the CO2?

Betcha $5 no one does this, much less get to the bottom of whether or not the CO2 is, in fact, the culprit. 

figured it was best to disassemble gear after show...

A wise choice!

[hexyjones]

What is bit transparency...?

What is your standard for something to declared "Bit Transparent"

Also Im a bit unclear as to what qualifies as a test...

[Brian Skalinder]

What is bit transparency...?

Bit-transparency = the device (or devices in the chain) do not modify any of the samples within the bitstream, i.e. passing a WAV through the device chain over and over again always yields exactly the same output WAV as input WAV.

What is your standard for something to declared "Bit Transparent"

I'm not sure who you're asking, but my personal standard:  if I test it and it proves bit-transparent with my combination of gear.  Or if someone else performs sufficient testing with appropriate documentation and rigor.

Also Im a bit unclear as to what qualifies as a test...

It depends on your gear.  The simplest test would be something like this:

[1]  Identify WAV₁ on your PC
[2]  Stream WAV₁ from your PC through your known bit-transparent soundcard using S/PDIF
[3]  Pass the S/PDIF WAV₁ into the CO2 S/PDIF connector and out the CO2 optical port
[4]  Record the CO2 optical output onto a JB3
[5]  Copy the new WAV on the JB3 back onto the PC as WAV₂
[6]  Trim WAV₁ and WAV₂ to the same starting/ending sample
[7]  Compare WAV₁ and WAV₂ with a WAV compare utility, like the one in EAC
[8a] If the WAV compare returns no results, i.e. no differences between WAV₁ and WAV₂, then this particular test demonstrated bit-transparency for the gear combination involved
[8b] If the WAV compare returns results, i.e. identifies differences between WAV₁ and WAV₂, then this particular test demonstrated the gear combination involved is not bit-transparent

However, a single test run is not sufficient, IMO, and we must perform this test over and over and over again.  How many times over?  I dunno, we probably all have different standards that we would consider appropriate.  And, of course, the above test does not take into account the particular gear one would use in the field.  So if we proved the above combination of gear bit-transparent, it would not necessarily follow that if we replace the PC with a field ADC we would achieve the same results.

And so, testing field gear is even more difficult, and requires that the field ADC have two outputs - one to produce a control WAV, and the other a test WAV.  In my case with the ODL-312, I ran my field gear as though I was, well, in the field, and determined that with my gear, in the field, the ODL-312 proved bit-transparent.

[hexyjones]

Can I do this with a CD player with digital out?...I dont have a PC with digi out...

[Brian Skalinder]

Can I do this with a CD player with digital out?...I dont have a PC with digi out...

Hmmmmm...maybe, but then you'd have to ensure your DAE of the WAV from the CD is perfect as well, not a super-easy task unless you already have EAC set up to do so properly.  And, at any rate, it wouldn't actually prove the CO2 is bit-transparent in the field with your particular gear, which IMO is the real question.

[hexyjones]

Can I do this with a CD player with digital out?...I dont have a PC with digi out...

Hmmmmm...maybe, but then you'd have to ensure your DAE of the WAV from the CD is perfect as well, not a super-easy task unless you already have EAC set up to do so properly.  And, at any rate, it wouldn't actually prove the CO2 is bit-transparent in the field with your particular gear, which IMO is the real question.

I wonder if you burned the wavs as data - do some DVD players read that kind of disc...as if they were mp3s?

[Brian Skalinder]

I wonder if you burned the wavs as data - do some DVD players read that kind of disc...as if they were mp3s?

Dunno.  I know mind doesn't, but it's sorta old.  But again, IMO, proving the CO2 bit-transparent in that scenario doesn't help us because our real concern is how it performs in the field with a different combination of gear.

[hexyjones]

Isn't it true there is a great deal of variation in the implementation of SPDIF spec?


And - I understand the comparison method..but...

Is there anything one can look for in an existing recording to detect any problems?

Wouldnt some software complain if there were samples missing?

[Brian Skalinder]

Isn't it true there is a great deal of variation in the implementation of SPDIF spec?

As I understand it, yes.

Is there anything one can look for in an existing recording to detect any problems?

If you drill into the wavform closely enough - and I meany *really* close - you may be able to see misplaced or dropped samples.  Some WAV editors may have a way of doing this automatically, but [1] they may not be precise, and [2] I'm not certain if they actually do.

Wouldnt some software complain if there were samples missing?

Nope.

[SparkE!]

Brian, my hope is that by understanding the design limitations of the CO2, we can more easily predict when its use with some particular type of equipment will work and when it will not.  Knowing those things will not reduce the imporance of testing for bit accuracy, but it can help us to avoid wasting time testing combinations that have no chance of working.

For what it's worth, I like my ODL-276 and it has worked well with every piece of gear to which it has been connected.  I don't see any reason that I'll ever be in the market for a CO2.  On the other hand, I don't necessarily look down my nose at recordings that were made with a CO2 in the lineage, but it does make me wary of the source.  Normally I would prefer a source whose lineage did not involve a CO2.  (Yes, I too am guilty of stereotyping the CO2, but I'm trying to be more open minded. )