'Bit are bits' poll
- Thread starter ItemAudio
- Start date
I agree. In the context of the questions this means voting 3 or 4. I voted 3 because I have not heard the uber premium dacs costing tens of thousands of pounds. I think most real world dacs benefit from having less electrical noise regardless of the fact that the data stream is bit perfect.
There are some measurements (yep actual facts!) here that can be interpreted in many ways, but that certainly do seem to show how much more susceptible a DAC is to computer noise when using its unbalanced outputs compared to its balanced ones. Conclude what you will. Bits are bits for sure, but bits plus noise is fewer bits.
sonddek
Trade: SUPATRAC
That is a very interesting thread indeed. Thanks. It suggests the benefits item hears in quiet transports may accrue in a DAC's output cables!
.. or (more likely perhaps) in the output stage. But if you connect a DAC to a massive source of noise at one end (a pc) and don't do much about it, it's not surprising that some of that noise can get out the other end. But spending money on quieting the transport is arguably throwing good money after bad; why not spend money on a better designed DAC that is better isolated from the electrical noise of the pc? For example, Naims new V1 optically isolates the digital and analogue sections. Other DACs make claims about galvanic isolation. Good to see these things being measured rather than just speculated about.
item's business model is pretty decent and straightforward imo. Listen to whatever of his you are interested in for a week and make your own mind up. Buy it if you want. Pay for the postage back if you don't. If you've got a DAC that is affected by a noisy source then it's up to you whether you buy a quieter source or a less susceptible DAC or balanced cables. item can supply any of them. You can make your mind up. The measurements I linked to indicate there may be a measurable basis for some of the phenomena talked about here. Anyone can challenge those measurements with measurements of their own and/or interpret them in many different ways.
Er - but you're suggesting (and that tends to be the case anyway) that the DAC fixes the problem, ergo no need to worry about the source. I wouldn't disagree.
Don't hide away such a helpful thread in the trade section. It would be much better received if you post it (rather than me!) in the main forum, Andy!
Nothing that heaps of folks haven't already found out by good ol' trial and error listening . . .
Always better to solve the problem at source: given that DACs and systems vary so much with regard to susceptibility.
sq225917
Bit of this, bit of that
Does that really tell us anything more than noise from the source PC may manifest itself as common mode noise on the outputs of the dac under test. It doesn't tell us if this is directly audible, just that it throws the measurements off on the soundcard performing the Rightmark tests when using the single ended inputs.
It's a good start for sure.
It's a good start for sure.
darrenyeats
pfm Member
My interpretation of that thread is that the noise is picked up by the CABLES because by using balanced cables (common mode rejection) most of the noise is absent.
Darren
Darren
sonddek
Trade: SUPATRAC
From the point of view of the analogue output stage of a DAC, a digital signal is noise, on a massive scale. It's an absolute roar. Think 33k modem signal. So this idea that poncing around with jitter rates is somehow going to immunise a DAC which leaks noise is a bit silly.
My TOSLINK cable cost about 2 quid. If I had known I was implementing a state of the art "galvanic isolation solution" for leaky DACs, I would have put it in a fancy box and flogged it for three hundred quid.
A DAC which lets miniscule timing variations from the input data through into the analogue signal is a shit DAC and needs a much better buffer. The thread and measurements linked to said nothing of that sort was happening. The measurements suggested that the proximity of a computer to unbalanced output cables was transmitting noise into them. Efforts to differentiate sources (e.g. ethernet vs wifi vs properly shielded output when the DAC was driven by USB) in any significant way were a spectacular failure. The linked experiments do not back up the idea that it's worth spending money on a transport. They do support the idea that it's worth using XLR outputs from a DAC if it's near a noisy computer.
Note the first test manages to establish practically no difference between XLR output measurements when the PC is idling and when it is running full tilt. According to item's broad listening experience, this fellow's testing equipment must be broken broken. Here's the point: "In theory I would have expected that a busy machine worsens "jitter" through the USB interface with all the audiophile talk about minimizing # threads and CPU load... At least no evidence from my tests to suggest this makes any difference SO LONG AS YOU MINIMIZE ELECTRICAL NOISE from getting into the system."
Note also that even the difference between XLR and RCA output is probably near or below the inaudible threshold: "However, the RCA 'quiet i7' (white) has a number of spikes evident including a -115dB hump at the 60Hz powerline frequency (of course this is inaudible at normal volumes)."
This is his conclusion: "If you're listening with the computer, computer LOAD could make a difference but if your equipment has good noise rejection (eg. use of balanced cables), this does not seem to be an issue... If computer load correlates to USB jitter, I'm not seeing it showing up in these measurements either because the asynchronous DAC is doing a good job rejecting it or the increase in jitter is not enough to overpower the existing jitter in my measuring equipment."
How anyone can turn that into a win for foo transports I have no idea.
sonddek
Trade: SUPATRAC
What problem at source? The linked tests strongly suggest there isn't one.
adamdea
You are not a sound quality evaluation device
Me neither. It's very disappointing when you bother to read some link which supposedly proves a point and find that it does nothing of the kind.
Thing is, whereas the supply of information which backs up even a very sound proposition is limited, the supply of information which does not back up a proposition is unlimited.
So, more to come.
It doesn't look like the Squeezebox forum member was trying to prove a point: he was just exploring stuff. I commented on page 10 that it was interesting and helpful, and repeated my usual maxim about the desirability of fixing causes as well as symptoms, and the primacy of listening. Seemed like a good moment for a recap . . .
IWC Doppel
pfm Member
Not being too technical and prepared to experiment.... when it became obvious soem years ago that CA and various transports sound different, for me this Must be about what the digital chain adds rather than what might be missing. For me bits might be bits but that explains very little.