Attenuators & Jitter Reduction

[jkeny]

The SPDIF stream as you may know is a single bit stream that contains the data and the clock frequency 'encoded' within it. At the receiver end, this clock needs to be extracted from the stream. ALL digital bitstreams will contain jitter. It cannot be avoided, even if reflections are present or not. Again, how much of it there is, is down to implementation and the designer. The extracted clock will in effect be derived from this incoming stream. Therefore it will inherit any jitter already on the SPDIF stream. Using multi-stage PLL's can reduce this jitter but it can be tricky. So if this 'jittery' clock is now used to clock a DAC it will drive the DAC with subtle timing variations which is not ideal.

Yes jitter is unavoidable but it is also cumulative so there is no need to add reflection generated jitter if it can be avoided. Multi-stage PLLs are great in theory, implementation is another thing

Some DAC's can be clocked separately using a dedicated high precision crystal, therefore not inheriting any jitter from the SPDIF stream. But you will then have transfer the normal data from the SPDIF clock domain to the DAC's own separate clock domain. This presents its own problems and there are various ways to deal with such as a type of 'flow control'(which I posted about before on the old forum: dCS would use such a scheme over firewire I'm sure) or use Asynchronous Sample Rate Conversion or use low jitter locking PLL's. It can all get a bit theoretical from this point on. Normally this stuff is designed into the DAC chip itself so its not something than can be tinkered with at board level.

Just a few thoughts. I've written that off the top of my head so Im sure I've left out some of the finer details.

I agree that in theory it should be possible to make something that is almost completely immune from jitter but I would cite the ESS Sabre DAC as one of the most sophisticated re-clocking DACs around & yet the effects of a lower jitter source are easily heard. This is true of ASRCs also. It may not be just the clock that is carrying jitter but possibly the data streams also, I don't know - I'm just speculating on why, to date, there has never been a jitter immune DAC created!

[DaveF]

I agree that in theory it should be possible to make something that is almost completely immune from jitter but I would cite the ESS Sabre DAC as one of the most sophisticated re-clocking DACs around & yet the effects of a lower jitter source are easily heard. This is true of ASRCs also. It may not be just the clock that is carrying jitter but possibly the data streams also, I don't know - I'm just speculating on why, to date, there has never been a jitter immune DAC created!

I reckon that with ASRCs it is data jitter, not clock jitter that is the problem. No matter how much you interpolate(the basic principle behind ASRC) between the data points you're always going to be a tiny tiny bit out. It's the old question that comes up time and time again for digital audio designers: Which yields the better sound?

The right data at the slightly wrong time or the slightly wrong data at the right time? :-)))))

[jkeny]

So we do agree then that reducing the reflections on the cable is going to go some way towards a better, lower jitter, sound, no matter what the digital receiver involved?

[DaveF]

So we do agree then that reducing the reflections on the cable is going to go some way towards a better, lower jitter, sound, no matter what the digital receiver involved?

Of course. Any jitter reduction technique is good as it reduces the chances of any 'contaminants' modulating out onto the final analog signal. Cable reflections, source clock&data and the receiver will all contribute to the jitter spectra to some degree. Whether the sum of all this is audible or not is all down to implementation of course.

[Ken Moreland]

Interesting discussion on jitter and attenuation. From John's description of a digital cable it is almost impossible to predict the effects of a digital cable unless it is manufactured to very high standards,contains no anomalies and presents an impedance of 75 Ohms. Even then the length has capability to affect the sound to some extent due to reflections.
When I installed the JK Hiface I used my digital cable from the CD player to connect to the DAC and The Benchmark DAC1 has only one of each RCA , Toslink and Balanced inputs. To use my CD player meant plugging/unplugging the digital cable so I used a plastic Toslink one which was similar or slightly inferior to the digital cable (LAT International DI-20). I replaced the plastic Toslink cable today with a glass Toslink from Wireworld and the sound is greatly improved over the digital cable. Looks like the digital cable is not as good as it could be and I'm hoping the attenuator when it gets here will improve it.

[jkeny]

Interesting discussion on jitter and attenuation. From John's description of a digital cable it is almost impossible to predict the effects of a digital cable unless it is manufactured to very high standards,contains no anomalies and presents an impedance of 75 Ohms. Even then the length has capability to affect the sound to some extent due to reflections.

Exactly right, Ken. Cables are a minefield & so are a rich mother-load for snakeoil salesmen charging up from €100

When I installed the JK Hiface I used my digital cable from the CD player to connect to the DAC and The Benchmark DAC1 has only one of each RCA , Toslink and Balanced inputs. To use my CD player meant plugging/unplugging the digital cable so I used a plastic Toslink one which was similar or slightly inferior to the digital cable (LAT International DI-20). I replaced the plastic Toslink cable today with a glass Toslink from Wireworld and the sound is greatly improved over the digital cable. Looks like the digital cable is not as good as it could be and I'm hoping the attenuator when it gets here will improve it.

One thing that is often talked about with cables is synergy. What I always interpret this to mean is that the cable is adding it's own sound & being used to compensate for some sonic shortcoming of the device it is connected to. Let me give you an example - the almost universally agreed synergistic SPDIF cable to use with the stock Hiface is the Oyaide DB 510 silver cable. It seems to tame down some mid/HF brightness that the stock Hiface has. Somebody who changed to the JKHiface reported that the attack & transients of the JKHiface wasn't as good as the USB input on his MisterX y2 DAC. It turned out that the Oyaide cable was now killing the transients/attack of the JKHIface.

My lesson from this is don't use cables to tune your system as they will probably be a lost investment when/if you change your system.

Ken, it would be interesting to compare your LAT DI-20 against a cheap no-name SPDIF cable + attenuator.

I just looked up the LAT cables & I have to quote something from their site " If you order with RCA connectors, you will receive the 75 ohm version" - there is no such thing as a 75ohm RCA connector, I'm sorry to say!

BTW, Ken, Toslink is said to be worse than SPDIF for jitter!

[Ken Moreland]

Hi John, I was aware that there were question marks over Toslink's performance and the reputation for jitter, I went ahead with the glass one to give it the best chance of at least keeping up with the LAT cable and was pleasantly surprised with the result.
I'd agree with your views on cables in general , I don't think there's a cable made that doesn't have it's admirers and detractors and it's impossible to pick one without trying it beforehand.
KM

[Derek]

I put an attenuator (borrowed from Fran on the night of his gathering) in between my Transport and DAC, dropped on Jennifer Warnes - “The Hunter” and the hairs on me back refuse to sit down.
It’s a hell of a difference.
More music!

Rammstein “Du Hast” from their 1997 album SEHNSUCHT, (it’s gonna be a long night), wonderful detail behind the driving guitar and keyboard, power and timing really dialled in.

The Bee Gees – “This is where I came in” opening track, stunning.
For those of you not familiar do yourself a favour and get a listen.

Alabama3 “Woke up this morning” from EXILE ON COLD HARBOUR LANE. What can I tell you everything sounds better.

The Propellerheads version of “On Her Majesty’s Secret Service” from SHAKEN & STIRRED; The David Arnold - James Bond - Project.
Tight and clean; as in, any flabbiness from the bassline is gone.

Lemon Jelly, “Nice weather for Ducks”
Gov’t Mule, “Mother Earth”
Paul Simon, “Diamonds on the soles of her shoes”, “The Cool, Cool River”

Time to stop scribbling and just get down to listening, next Johnny Dowd.

The true ability of this Transport and DAC is shining through, Fran many thanks you’re not getting the wee magic yokey back.

[Fran]

Yup, thats what I heard too....

Fran

[Ken Moreland]

Got my 10dB attenuator this morning from Estonia ,(2 weeks after ordering and for 22 euro all in), stopped whatever it was that I was doing and started to install it. The Benchmark DAC1 has a BNC input with an adaptor for RCA cables so the attenuator fitted in without additional connectors, switched on the Hiface and the dac locked on without any problem. Listened to ripped CD's in EAC .wav format, then Hi-res files in 24bit format.
There is a major improvement in sound quality across the board. The album Astral Weeks Live at the Hollywood Bowl has Van giving his usual mumbled delivery but this became clearer and more articulate. Every album has improved definition, better,clearer bass and no high level tizz. On Hi-res, Barb Jungr on Linn Studio Master of Every Grain of Sand was superb and Rickie Lee Jones on an SACD rip from Pirates was smooth and had great drum wallop. On regular CD her voice can sound so high it is headache country.
Tried the 10dB in between Teac transport and dac and again the sound was superb but the track skipped once(never before) and righted itself before I could check if the dac has lost it's lock.
The attenuator is for use with the Hiface and it is a further improvement on it's performance. It's a very low cost investment for such an improvement.