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In Reply to: RE: 'I just don't feel that wireless, USB or firewire are robust enough for streaming audio.' posted by Crimson on March 19, 2008 at 16:23:27
Really? Not IMO.
Follow Ups:
I asked for your feelings about the lack of robustness in the stated connections of wireless, USB, and FW. Care to answer?
--eNjoY YouRseLf!.....
Uh...no...you go first. My feelings are reserved for my wife and my therapist.
Why would SPDIF, which is designed to transport digital audio, be the last method of connectivity to use as far as digital connections?
USB's limited distance speaks to its frailty. Ditto with wireless. Wireless can be disturbed too easily: walls; angle of signal propagation; etc. USB and firewire require special purpose drivers utilizing complicated programming.
There is no need to rely on methods not purposely developed for digital audio to transport digital audio when purpose-built digital audio methods are commonly available.
"Why would SPDIF, which is designed to transport digital audio, be the last method of connectivity to use as far as digital connections?"
Because S/PDIF is such a poor design. It was done cheaply and simply for mass-market consumer gear. No error correction, length limitations, encoded clock, no packet-mode transfer. If S/PDIF had been designed with a separate clock, then it might be interesting, but it would still need packet-mode transfer with handshaking and re-transmission.
Steve N.
'It was done cheaply and simply for mass-market consumer gear.'
It's also used on a lot of high-end audiophile gear. And its beauty is in its simplicity.
'No error correction, length limitations, encoded clock, no packet-mode transfer.'
Length limitations compared to wireless? Or USB? Toslink can easily go 10 meters without a problem. Coax can easily go 15 meters. Again, its beauty is in its simplicity.
'If S/PDIF had been designed with a separate clock, then it might be interesting, but it would still need packet-mode transfer with handshaking and re-transmission.'
I use a re-clocker after the 10 meter cable.
Mike
"Length limitations compared to wireless? Or USB? Toslink can easily go 10 meters without a problem. Coax can easily go 15 meters. Again, its beauty is in its simplicity."
Not beautiful to me. The jitter caused by long cables like this or Toslink is very high.
What kind of reclocker are you using, a Big Ben perhaps?
Steve N.
'The jitter caused by long cables like this or Toslink is very high.'
How high? I won't speculate how high or how low the jitter is in my 10m toslink.
I use a Theta Time Linque Conditioner.
I read the test results on these de-jittering devices. Not very good results IMO. It seems to me that the test set-up must have had a fairly bad ground-loop of some kind as all of the wired results were actually worse than the original jitter. Only the Toslinks seemed better.The Theta TLC evidently has a transformer coupling the S/PDIF output, but like many manufacturers, it is wired as an auto-transformer which eliminates the galvanic isolation. It sounds a lot like the DDDAC which uses a free-running oscillator and an 8412 or 8414. The way this works is that as it "precesses", it throws away samples from the input stream to avoid sync problems. Not bit-perfect, but one way to sync the stream to an asynchronous clock.
These results are actually not so great - 0.5 nsec to 1 nsec of jitter. The risetimes of some of these are 2-3 nsec, so the jitter should not be this high. Probably a result of using inexpensive oscillators, or at least not the best choices IMO.
Steve N.
"I read the test results on these de-jittering devices. Not very good results IMO."Maybe you should have read the methodology. They intentionally started with high jitter levels. Quoting the article, 'For this test, a rig was assembled using a conventional CD player (with coaxial and optical digital outputs) and an outboard DAC whose digital interface offers little or no jitter attenuation. Data-pattern jitter was stimulated using a mixed-tone signal based on fractions of the 44.1kHz sample rate (first suggested by Julian Dunn at the 93rd AES Convention). Analysis, in the analogue domain, was completed using proprietary Vl (Virtual Instrument) software.
Both Type I (phase-modulation) and Type 2 (phase and amplitude modulation) jitter are revealed as symmetrical and asymmetric sidebands, respectively, appearing either side of the final analogue signal (4): see the reference spectra. Importantly, this test provides a direct indication of the audible distortion caused by digital jitter and the effectiveness of each 'jitter buster' as it is placed between the transport and DAC.
The total data-induced, peak-to-peak jitter generated via the CD player's coaxial digital output was computed to be 1584 picoseconds. The same test was repeated to determine the inherent jitter-level of the CD player's optical digital output, which amounted to 3241ps. The latter is about 10-times higher than ideal for a decent CD player and represents a hearty meal on which our 'jitter-busters' could dine.'
"The Theta TLC evidently has a transformer coupling the S/PDIF output, but like many manufacturers, it is wired as an auto-transformer which eliminates the galvanic isolation."
True, but quoting from the article 'Via the optical input, this ground link is broken, thereby exposing the true potential of Theta's design; in this mode, jitter falls by 82% from 3241ps to 575ps.'
"It sounds a lot like the DDDAC which uses a free-running oscillator and an 8412 or 8414. The way this works is that as it "precesses", it throws away samples from the input stream to avoid sync problems. Not bit-perfect, but one way to sync the stream to an asynchronous clock."
Well Steve, there is no need to guess if you read the test results. Quoting from the article again, 'The TLC uses a free running PLL within the CS8412 interface for clock recovery and jitter suppression without a second crystal-based lock (as used by Audio Alchemy, for example). The digital output is re-clocked via a D-type flip-flop with extra 'signal conditioning provided by a high-speed hex inverter—hence the TLC's high output level, clean waveshape and fast risetime.'
Steve, are you making a claim here that the Theta Timebase Linque Conditioner throws away samples to achieve its purpose?
"These results are actually not so great - 0.5 nsec to 1 nsec of jitter."
The EMU 1212M specs claim 'Ultra-low jitter, clock subsystem: < 1 ns in PLL mode (44.1kHz, Opt. S/PDIF Sync)'. And the test results from the other commonly discussed products on this board are where?
"Steve, are you making a claim here that the Theta Timebase Linque Conditioner throws away samples to achieve its purpose?"
It has to if the design is as described. Read the description of the DDDAC. Identical implementation I believe:
http://www.dddac.de/ma_dac21.htm
Ultra-low jitter in my book is 10's of picoseconds, not 1nsec.
Steve N.
...per the linked circuit diagram, the DDDAC is not implemented like the Theta TLC. The DDDAC has the digital receiver (CS8412), an XO Clock (additional crystal oscillator), a 12-stage binary ripple counter (74HC4040, used for the D-type flip-flop?), and no high speed hex inverters. Compare and contrast that to the description offered of the Theta TLC:
"The TLC uses a free running PLL within the CS8412 interface for clock recovery and jitter suppression without a second crystal-based lock (as used by Audio Alchemy, for example). The digital output is re-clocked via a D-type flip-flop with extra 'signal conditioning provided by a high-speed hex inverter—hence the TLC's high output level, clean waveshape and fast risetime."
You are correct, if there is no oscillator in the device then it is not the same design. Too bad. The DDDAC although dropping a few samples actually has a much better chance to achieve really low jitter.
Steve N.
And the test results for the products to which you are alluding, the ones with ultra-low jitter of 10's of picoseconds, are where?
'Read the description of the DDDAC. Identical implementation I believe:
http://www.dddac.de/ma_dac21.htm'
Sorry Steve, aside from using the same receiver, I see nothing identical in the implementation. Maybe you would like to point out the exact text that points to an identical implementation.
So, you are a manufacturer. And you say that the Theta TLC has to throw away samples. Putting aside the Theta for the moment, where does it state in the link you provided that the DDDAC (which apparently has many versions) throws away samples? Is it your understanding that it's the only possible way that it can stay sync'd?
Yes, it is the only possible way that it stays synced. It must throw away samples. This is a feature of this particular receiver, and the DDDAC takes advantage of this. If the local clock is tuned fairly close to the stream source, then the drops are infrequent and probably not audible. If the stream and the local clock are different in frequency by say 1000PPM, then it may become audible IMO. This would be a missing sample about every second.
Steve, I realize that raw jitter numbers expressed in ps or ns mean nothing out of context. But, in your opinion, can you state what you believe to be the threshold level, above which, jitter can become audible? I don't mind if you want to put it into context, or whether it is stated in ps, ns or ppm. And I realize there have been studies on the matter. And that the studies are not consistent. But what is your opinion? I don't feel like I can hear jitter in my current setup, as I've heard it described many times.
I have devices now with extremely low jitter. Cannot be measured on a scope at 3nsec per division. I have to believe that below 200-300psec it is pretty much inaudible in the very best systems on the planet. You have to understand that a system capable of discerning this is a world-class system with extremely low noise and sibilance. I believe only about .1% of systems in existence are in this league. Every component in the system, and the cables must be the very best, and modded not stock. No combination of stock components is capable of this level of performance IMO. When I do an A/B test of jitter, virtually every listener hears the difference. The effect is not subtle in an ultra-quiet system.
If you are not hearing differences in jitter, you are not alone. Most systems have enough other noise and sibilance to drown it out.
Steve N.
> > Uh...no...you go first. My feelings are reserved for my wife and my therapist.
You stated 'I just don't feel that wireless, USB ...........'. Thus my query of your 'feelings'.
> > Why would SPDIF, which is designed to transport digital audio, be the last method of connectivity to use as far as digital connections?
Please reread my post: 'SPDIF from a computer ........'. The reasons are obvious.
> > USB's limited distance speaks to its frailty. Ditto with wireless. Wireless can be disturbed too easily: walls; angle of signal propagation; etc. USB and firewire require special purpose drivers utilizing complicated programming.
Distance limitations? I guess SPDIF doesn't have any. Walls and angles of propogation? We're not talking microwave line-of-sight frequencies here. Special drivers? Only if it's a non-compliant appliance (dacs do not fall in the non-standard category).
--eNjoY YouRseLf!.....
Oh yes we are!
2.4 GHz is "microwave" and it is certainly "line of site" since it doesn't have any reliable propagation modes terrestrially beyond the horizon. Since it does partially propagate through dry, non-conductive materials it can be used on the other side if the S/N is sufficient. Typically the worst problems are multi-path cancellations (oh dear, there's that angle of propagation) which is why the fancier access points and clients have diversity antennae.
But it should work perfectly for audio if it does for data, it certainly seems to.
Radio Rick
In other words, you have no reason why SPDIF, which is designed to transport digital audio, should be the last method of connectivity to use as far as digital connections.
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