|'); } // End -->|
In Reply to: Re: How do digital cables affect sound? posted by email@example.com on January 6, 2007 at 12:47:46:
> You are correct to say digital signal is nothing but 1's and 0's, but
> the odd harmonics cause signal smearing and ground noise.
Are you saying the "odd harmonics" create new 1's and 0's that weren't there or destroying ones that should be?
I follow the jitter argument since it is important at what precise point the information in the 1's and 0's is returned to the analog state. But to create "ground noise" in a digital state means totally new info needs to be created. If digital were susceptible in this fashion, no computer program - which can't tolerate any errors - could be installed.
"Are you saying the "odd harmonics" create new 1's and 0's that weren't there or destroying ones that should be?"
No....harmonics create noise on the ground. This is why the pro industry prefers AES/EBU for all digital and analog signal connections.
You're still using an analog concept in a digital realm. Noise in the background of a digital cable doesn't mean anything as long as the receiving end of the system can differentiate whether a sent bit is a one or a zero. The analog signal to noise ratio concept does not function in the same fashion in the digital world. You can run over 300' of cheap twisted pair CAT5 cable and have bit perfect transmission at 100 Mbps to the other end in a computer system. (That's about 70 times faster than a CD bit stream needs. Plenty of head room for error correction as needed.)
If noise does become a problem, that means you are either "creating" new ones and zeros that are being read at the receiving end or you are completely dropping existing ones.
Interesting that we can send 40 million lines of code in an XP network install without a problem but if the data contains music it all of a sudden becomes susceptible to all manner of old analog problems.
wonderful aspects of digital communication are unnecessary overhead put in place by nervous nilly engineers? You're pretty funny!
Sure it works fine with computer networks, if there is a problem with the data, it is just requested again and again until it is correct. digital audio doesn't work that way.
> if there is a problem with the data, it is just requested again and
> again until it is correct. digital audio doesn't work that way.
Actually audio does work that way. If there is an appropriate buffer at the receiver end (jeez, even car CD players include a buffer) then there is plenty of time to get a good signal to the buffer. That buffer can then parcel out the data to the DAC are just the pace required. For example, I can unplug the CAT5 cable on my inexpensive Squeezebox 3 and it'll continue playing perfectly fine for 8 to 10 seconds. At 1.4 Mbit/sec CD speed that's enough time to transmit 125 gigabytes of data on a 100 Mbps network.
As I noted previously, jitter is a very legit issue, but there are very good ways for the equipment to work around that and the issue has been discussed at length here and a lot of other places. I have to question how well designed a piece of equipment is if it is sensitive to cable-induced jitter.
Toslink and SPDIF are not network connections and do not buffer data. I agree that it would be easy to do. Many new home cd players are starting to spin the disc faster than 1x and buffer the data. I have not heard of any external DAC's that buffer incoming data.
John Watkinson (author of the book "The Art of Digital Audio") said in the July/August 2002 edition of Resolution (UK audio magazine) "...On the other hand, if the DAC has not been properly engineered, changing the cable could affect the amount of jitter reaching the converter. Thus we finally have a practical use for exotic cables as DAC testers. If the use of an exotic cable makes a DAC sound better, then the DAC is not performing adequately and should be repaired or redesigned."
have you ever experimented with different digital cabling between a transport and a DAC? There is definitely something "odd" going on here, and in many cases, that "oddness" is quite audible. My guess is that VSWR based signal reflections cause timing based problems, resulting in shifts in clocking. A lack of focus and an increase in smearing is the end result.
With the above in mind, my best results have been with digital cables that are resistively terminated at the load end. This technique of impedance matching is old school, but still quite cheap, easy and effective. While Stereophile ran a small article about this a few years back, and promised to have a follow up article and never produced, i'm not aware of any manufacturers currently using this technique in a production based cable. That's too bad, as i've definitely seen the benefits of such an approach. I was using a similar method to what the Stereophile article mentioned several years before the article was ever published.
For that matter, i'm not aware of any transport or DAC manufacturer that offers some type of user adjustable input or output impedance compensation networks. While such an approach would be inexpensive to impliment and could solve a lot of problems, it seems as if they are more interested in spending big money on cosmetic upgrades than actually improving performance. I guess that they are simply catering to the market, as there is certainly a large portion of audiophilia that assumes that better looks equate to better audible ( not necessarily better electrical ) performance.
Outside of transmission line and / or input/output impedance compensation, a DAC that re-clocks the incoming signal can also help quite a bit. While more expensive and complex than the very moderately priced impedance based compensation networks previously mentioned, such an approach can take further steps towards preserving signal integrity and improving aural performance of the system. Implimenting all of these aspects of component design and integration into one's system simultaneously can make for a VERY enjoyable aural digital presentation while satisfying even the pickiest of electronic tinkerers. Sean
This post is made possible by the generous support of people like you and our sponsors: