Tír Na HiFi

rickmcinnis wrote:What is PFM?

Swenson has all kinds of things to say like that but the reality is we are stuck with what we have and have to find out how to do the best with it we can.

I know Dave Daqvenport (RALEIGH AUDIO/K&K Audio) knows his grounding stuff and says he has incorporated some sophisticated techniques into his DAC board. Poured grounds; he has a paper on grounding , in general, at his site. http://www.raleighaudio.com/Audio%20Com ... ection.pdf - worth a read.

I have somewhere another of his papers - hope I have not lost it, that goes into his experiments with poured grounds which was from a conversation he had with Bud Purvine, who came upon this idea (the link is to someone who makes the things - http://tweakaudio.com/EVS-2/EVS_Ground_Enhancers.html) which is somehow an implementation of an instant poured ground. Seems to be something like an electron sink or source - an active ground? I am way over my head here!

Anyone looked into this? I have tried the product linked at my loudspeakers and it does add a bit of refinement to the sound.

Like sima was talking about: weird things that make the sound better.

sbgk wrote:in case people hadn't seen this

http://www.audioasylum.com/forums/pcaud ... 26159.html

HI JE,
I'll try and give some real life examples here of how things other than "the bits" could have an affect on the analog output.

I've been working on a new USB DAC design recently, so I have a setup that I'm continuously looking at with scopes and logic analyzers etc. In this situation the logic analyzer said everything was fine, the bits were perfect. A logic analyzer runs the analog voltage on the wire through a "threshold" to distinguish if it is high or low, what you see on the screen is just high or low, ie "bits". But when I looked with the scope which shows the actual voltage levels of the signal I saw some extra signal riding on top of the highs and lows of the "bits". This turned out to be noise on the ground plane caused by the processor that was generating the bits. (it was much worse than it should have been due to a poor board layout of the processor reference board) That noise was enough to cause significant change to the audio out even though the "bits" were correct.

One interesting aspect of this was that you could easily see changes in this ground plane noise depending on what the processor was doing. While this was a fairly gross example of the effect, it clealy shows that things going on in the processing and transmission of the bits can have an affect on the sound at the output, even though the correct bits get to the DAC chip.

Next you might ask "well isn't that a broken system, if it was "good" shouldn't it not be an issue?" Note that this was the official reference board for the processor made by the manufacturer, who should know how to make things that work well with their processor. This just goes to show that things that can cause audible differences in digital audio are frequently not part of "it works as a digital system", the board did what it was supposed to, it delivered the bits.

A better board design could have cut this ground noise down significantly, but it would still be there.

What we DAC designers have to do is figure out ways to design products that produce analog out that is immune to this sort of thing. Unfortunately this is extremely difficult to do. There are many people on this board that expect that this is easy to do, just put in the right 50cent part and presto the design is completely immune to everything. It doesn't work that way. High frequency ground noise is extremly pernicious stuff, it will find a way to get around just about any obsticle you throw in its path.

Different designers take different approaches to try and achieve this with varying degrees of success. The different approaches will usually be affective at decreasing susceptibility to different types of noise so one DAC model may not care about a certain aspect (say cable differences) while another may be pretty immune to cable aspects but be susceptible to timing variations in packets. This may be a part of why some people say they can hear certain aspects and others say they cannot.

These techniques for noise suppression are pretty esoteric knowledge, there really are only a few people that really understand all this, there are very few places in the real world were the combined knowlege to make this really work right are required, thus very few people have a good grasp on all of this. The result is that many actual designs on the market are fairly lacking in this department, or are only targeting one aspect of it.

This is slowly changing and companies are starting to get an inkling of what it takes to do well with this and are hiring people with some knowledge in this field, but there aren't nearly enough to go around, so it's going to be some time before all digital audio systems you can buy do a good job in this regard.

Sorry, I'll get off my soapbox now.

John S.

sbgk wrote:uploaded mqnplay, mqnloader and mqncontrol exes

if you put them into c:\musicplayer directory and put a wav file called test.wav in that directory as well you should be
able to double click on mqncontrol to play it.

the mqnplay file will need the device changed

Hopefully have it all working with devices and normal file load next week, but if anyone is keen enough I think it's worth a try to hear what it sounds like.

should also work in AO core as have removed the wasapi bits.

for haswell only at the moment

sbgk wrote: should also work in AO core as have removed the wasapi bits.