New Posts  All Forums:Forum Nav:

GW Labs DSP, first take - Page 2

post #16 of 21
7/12/02 at 7:52pm
In reference to the digital cable issue, the quality of cable affects not only jitter but the signal quality itself. This loss of quality can affects the clock recovery.

1. Inter symbol interference. As digital signal passes through the cable the signal is no longer 1 and 0. It looks more like an analog signal, the pulse start to spread. The signal between bit can add up and cause bit error. This can happens if your cable is very long.

2. Reflection. If the cable is not properly matched the signal can reflect and cause false reading of the 1 and 0.

3. Interference. If there is a noise hit and the cable has poor noise immunity, the noise hit depends on the polarity can cause bit error.

Some of these are unavoidable, that is why good engineering practice is have error detection. Unfortunately, SPDIF have no retransmit capability unlike TCP/IP. This makes digital transmission not very robust for digital audio.
Reply
post #17 of 21
7/12/02 at 10:10pm
As I said in my previous posts, digital cable can only have two effects: jitter or bit errors.

If jitter is eliminated by reclocking, only bit errors are possible. If there are bit errors, they will be very audible.

By the way, I know of a person at other forums that has been able to act himself succesfully as a digital cable, just wetting his fingers with salted water, and touching with them the output and input spdif connectors.
Reply
post #18 of 21
7/12/02 at 10:37pm

DAY THREE

Well, it just keeps getting better. I listened to Elvis Costello's "My Aim Is True" this evening, and WOW!!! It was almost like I was listening to him in concert!!! I heard details and subtleties in the vocals and background that I've never heard before.

I like it so much, I may consider KEEPING my AKG K-240's. It sounds that much better.

Color me satisfied....a highly recommended tweak!!!.


Reply
post #19 of 21
7/15/02 at 4:08pm
Hi Ricky;

My intention is not to dispute your opinion. However, I do think it is important to be accurate. There are many mechanism in cable that could cause bit error and I'm just pointing out some of them. (I'm in the digital transmission field for more than 10 years).

Bit error in audio don't always result in highly audible noise. There are two mechanism with digital audio. In the CD, the data are interlaced by using Reed-Soloman, and the the RS decoder can correct the bit error. That is why a CD should be clean from inside to outside. A circular scratch wipping out an entire frame can not be corrected.

The digital data is futhur "corrected" by auto-corelation. The DAC will output what it think is the right data. In this case the audio data does not result in pop or click unless the data is highly erroneous. I have CD that have high error that will play like pop and click in my vintage 80 CD player but no pop and click in my better CD player. Note that cheap SPDIF receiver (in hardware mode) will pass on the error unmodified.

So it is fair to say, a SPDIF non-compliant cable could sound worse than a compliant cable.

Jitter is a different beast. Jitter can be result of cable (again if the media is long and of poor quality, for example there is a small bubble in the plastic fiber) and from the transmitter itself. Cable cannot do anything for you if the jitter is generated by the transmitter.
Reply
post #20 of 21
7/15/02 at 7:22pm
Hi, dvw.

Quote:
Originally posted by dvw

The digital data is futhur "corrected" by auto-corelation.
I'm not sure what are you meaning here. Could you elaborate a little more on this, please?

Quote:
I have CD that have high error that will play like pop and click in my vintage 80 CD player but no pop and click in my better CD player. Note that cheap SPDIF receiver (in hardware mode) will pass on the error unmodified.
But the bad thing about spdif is that, unlike reedbook cd, is has no built-in error detection schemes (except very very basic ones - 1 parity bit for every 31 bits) or error correction schemes, so there's no way to be sure if the bits received are right or wrong, and, unlike reedbok cd, there is no redundant information to correct possible errors.

Quote:
So it is fair to say, a SPDIF non-compliant cable could sound worse than a compliant cable.
True, due to jitter or due to bit errors, if the cable is very long or very bad.

Quote:
Jitter is a different beast.
Well, very bad transmission may cause bit errors. Bad, but not so bad transmission, can just cause jitter.

Quote:
Jitter can be result of cable (again if the media is long and of poor quality, for example there is a small bubble in the plastic fiber) and from the transmitter itself. Cable cannot do anything for you if the jitter is generated by the transmitter.
Agreed. But any decent standalone DAC should be able to remove all that jitter. However, it seems that many actual DAC's don't.
Reply
post #21 of 21
7/15/02 at 10:47pm
I don't want to highjack this thread into a digital cable discussion.

Autocorrelation is a function that take the previous data to predict the current data that is lost (e.g. IPphone) or in error.

The function of jitter tolerance is a PLL function. This is a tradeoff betwenn jitter generation and jitter tolerance in design.

The SPDIF spec is not very good. Too high a limit in jitter and some cable is simply just bad. I remeber seeing one review of a high priced cable with 135 ohm impedance. A good digital cable certainly will help sound quality.
Reply
New Posts  All Forums:Forum Nav:
  Return Home