advertisement


MDAC First Listen (part 00100110)

Status
Not open for further replies.
Thanks John.

If Bel Canto reckon the balanced output is better isolated, it may be worth taking up Vinz's suggestion of an XLR to phono lead. Or maybe I'll just leave it as it is.
As I've posted elsewhere, the difference in sound between my analogue set-up upstairs and the main system always seems to come back to that digital 'edge', so I'll look at practically anything that claims to remove noise.

Great to hear that things are progressing well over there.
 
A bit late to the party - but I would be interested in a CD transport in an MDAC2 wide chassis.

Currently I use my 1996-vintage Meridian 508 as CD transport into the MDAC. I imagine that it would not be possible to clock-lock this to the MDAC2.

I'd be interested to hear any views on the quality of the 508 transport. I'm not really in a position to test any comparisons.



I have the Meridian 500 transport, version 2, which is probably pretty similar to the transport section of what you have. It was a replacement for my Linn Ikemi, which I sold (because I could get a decent price for it). My impression when I changed was that the Meridian is just short of, but very close to, the Linn as a transport into the MDAC.

That difference wasn't, and isn't, really significant to me because, despite some of the views expressed here recently, to my ears my modified Mac mini, even back then, left both CD transports standing. Several improvements have happened since then. I like the CD for casual listening, but for anything serious I would always use the Mini now, though I would like to know how well a moderate price modern spinner could compete.

Once some clock-locked transports are running, I would be very interested to know how much difference this makes, though I think I would be more likely to go for the Oppo option since I have to use the CD layer rips from my SACD collection. I used to run SACD from an old Oppo 980H with HDMI extraction into the MDAC, but the CD layer rips were better.
 
Thanks John.

If Bel Canto reckon the balanced output is better isolated, it may be worth taking up Vinz's suggestion of an XLR to phono lead. Or maybe I'll just leave it as it is.
As I've posted elsewhere, the difference in sound between my analogue set-up upstairs and the main system always seems to come back to that digital 'edge', so I'll look at practically anything that claims to remove noise.

Great to hear that things are progressing well over there.

You might need an XLR to RCA with an impedance transformer.

Also it's still not clear if the MDAC understands AES data. If you can ensure the Bel Canto CD1 really SPDIF through the XLR it should also work.

With all that considered, using the other outputs from your unit should be less risky.

Also using a toslink splitter or switch might solve a lack of connectors.
 
You might need an XLR to RCA with an impedance transformer.

Also it's still not clear if the MDAC understands AES data. If you can ensure the Bel Canto CD1 really SPDIF through the XLR it should also work.

With all that considered, using the other outputs from your unit should be less risky.

Also using a toslink splitter or switch might solve a lack of connectors.
I was under the impression that AES and S/PDIF were in fact pretty much the same give or take the output level and that pretty much all units will work, but come to think of it that was I think based on using a S/PDIF output into a dac with an AES input (i think this is the case with genelec speakers for example), so perhaps it doesn't work the other way round. That said I was not aware that there was any advantage in digital AES over S/PDIF
 
So perhaps it was just puff from whoever wrote the manual. Having sorted out a duff lead, I'll stick with optical for the time being. Thanks anyway.
 
Thanks John.

If Bel Canto reckon the balanced output is better isolated

David,

I'd just be guessing from there statement that the AES balanced output is transformer coupled - so yes it does offer better isolation and I can see no problem using this with the MDAC SPDIF RCA inputs, it will work, and offer greater common mode noise isolation.
 
You might need an XLR to RCA with an impedance transformer.

Vinz,

technically your correct, but a few years back I tried to make some TDR measurements of the AES 110ohms interface, but found it so far from the optimal impedance that its was a complete mess, it was hard trying to see what was going on the TDR trace.

The XLR connectors for starters are no where near 110ohms, and again the same for the output driver circuits we measured.

Basically the 75Ohms input impedance of the MDAC not going to upset things to much - its already a mess.

Also it's still not clear if the MDAC understands AES data.

From a Protocol standard, the AES is almost identical to SPDIF with just a few differences in "User Bits" which are of no practical consequence.
 
Vinz,

technically your correct, but a few years back I tried to make some TDR measurements of the AES 110ohms interface, but found it so far from the optimal impedance that its was a complete mess, it was hard trying to see what was going on the TDR trace.

The XLR connectors for starters are no where near 110ohms, and again the same for the output driver circuits we measured.

Basically the 75Ohms input impedance of the MDAC not going to upset things to much - its already a mess.



From a Protocol standard, the AES is almost identical to SPDIF with just a few differences in "User Bits" which are of no practical consequence.

Thanks for the explanation.
 
David,

I'd just be guessing from there statement that the AES balanced output is transformer coupled - so yes it does offer better isolation and I can see no problem using this with the MDAC SPDIF RCA inputs, it will work, and offer greater common mode noise isolation.
Not as good isolation as optical mind you. I can never see what's supposed to be wrong with optical. Perhaps a bit of jitter creeps through the ASRC,on the Mdac; but with the memory buffer on the M-dac2 surely it should be fine.
 
Not as good isolation as optical mind you. I can never see what's supposed to be wrong with optical. Perhaps a bit of jitter creeps through the ASRC,on the Mdac; but with the memory buffer on the M-dac2 surely it should be fine.

Yes, indeed optical is the best option for electrical isolation.

I worry that the input of the buffer will be processed at the incoming jitter rate, thus there will be a far chuck of processing going on with the "Input Jitter Spectrum", this can result in second order effects (RF products and Ground plane noise etc.) that finds its way into the analogue domain despite my best efforts.

The Human ear is just so sensitive!
 
The Human Ear and PsychoAcoustics causes the majority of us many headaches, in my experience. We often hear things that just aren't really there, when we listen again with a friend as a Witness :) hehe
 
ti33er,

I've worked long enough in HiFi that I have developed a sound reasoning and methodology for listening. I don't just work by myself, more recently with Dominik and Renata. On more then a few occasions Dominik has tried to catch me out by swapping the names of filters etc - and I've always spotted the "Blind test".

When you work with Audio everyday you subconsciously hone your listening skills. There would be times when both Dominik and I have not been listening for a "change" (say we where working on a different project, just with music playing though the system) when we pass comment that the system sounds different, and then discover some unexpected issue.

There are times when it gets too much (such as when we where designing the filters) but after about two weeks of intense listing during the evenings everything became much clearer, I learnt to recognise the differences between filters - where I could almost automatically say which filter was selected.

Even today, long after such intense listening trials I can now tell within a few moments if the correct filter is not selected (I use the Fast filter for measurement, and sometimes forget to set back to the optimal transient filter for listening tests).

I don't consider myself to have acute hearing, its just that designing HiFi is my profession as well as my passion - after a lifetime of work as with any profession you become expertly "trained" in the skill.
 
Certain mantras will be repeated endlessly no matter what reasoned counter-argument you put forward, John.

Some people actually want to believe that differences are imagined.
 
Hi John

I believe you and in your work, which is why am on the MDAC2 project...crying that I couldn't get a VFET too, so Ricardo has 'had to get one' in my place :-D

It wasn't really Filters I meant, am sure you know what to listen out for there ...more on cables (Digital Coax especially after wasting much money on much bunk) and other snake oil where I've thought I've heard a difference until tested with a friend/s and then we can't

No offence intended your direction, but do believe in an element of PsychoAcoustics when it comes to some things too


Paul :)
 
Hi John

I believe you and in your work, which is why am on the MDAC2 project...crying that I couldn't get a VFET too, so Ricardo has 'had to get one' in my place :-D

It wasn't really Filters I meant, am sure you know what to listen out for there ...more on cables (Digital Coax especially after wasting much money on much bunk) and other snake oil where I've thought I've heard a difference until tested with a friend/s and then we can't

No offence intended your direction, but do believe in an element of PsychoAcoustics when it comes to some things too


Paul :)

When you learn what to listen for (beyond a simple better/worse/same) and can identify it you only hear real differences.
 
Yes, I believe you really need to listen to music and recordings that you are very familiar with in order to detect differences. I don't buy the "fresh ear" argument in which some people argue that you should listen to unfamiliar recordings.

- Richard.
 
Yes, indeed optical is the best option for electrical isolation.

I worry that the input of the buffer will be processed at the incoming jitter rate, thus there will be a far chuck of processing going on with the "Input Jitter Spectrum", this can result in second order effects (RF products and Ground plane noise etc.) that finds its way into the analogue domain despite my best efforts.
Can you expand on this for me. I can see that for any input to a dac something is going to have to happen when each bit is received- presumably this would be equally true for S/PDIF or usb -something has to happen when a bit is read(?)

Is this problem specific to memory buffers or does it remain with any digital transmission? Is there any particular reason why the little spark of energy that occurs when the incoming bit is read into the buffer will cause more problems than when an incoming bit is received by the usb receiver, or I suppose when optical data is converted to electrical signal?

Is the problem here that if the incoming signal is more jittery there is a greater chance that the second order effect will be damaging. -I wasn't quite clear whether the transmission of this little glitch of energy might be equally problematic whether it was jittery or not. This problem intrigues me because it makes me wonder whether usb might be worse than S/PDIF: would it be transmitted evenly or in more jittery packets than S/PDIF.

Is it possible that you could alleviate the problem by somehow dithering the input of the data to de-correlate whatever second order effect there was?
 
Yes, I believe you really need to listen to music and recordings that you are very familiar with in order to detect differences. I don't buy the "fresh ear" argument in which some people argue that you should listen to unfamiliar recordings.

- Richard.

Agreed, but I'm not sure if I can face another round of the Wailin Jennys - they bring back to many bad memory's of the hard time at IAG China when we developed the 8200CD / MDAC and the Huge listening effort required during the original MDAC upgrade process.
 
Can you expand on this for me. I can see that for any input to a dac something is going to have to happen when each bit is received- presumably this would be equally true for S/PDIF or usb -something has to happen when a bit is read(?)

SPDIF is a far simpler interface with significantly simpler decoding circuits, and can be decoded at a fixed Clock rate with oversampled statistical analysis (IIRC so long as you can sample the edges at 3 - 4 times the data rate you can recover the Data "clockless".

The USB interface requires magnitudes greater circuit complexity, the more circuit devices you have operating at the USB Host data rate the more greater the level of PSU & Ground noise will can be injected into the system. This opens the door for a "Distortion" mechanism that allows the PC's operating domain to enter the Audio domain.

The Ideal solution is to remotely situate the USB input circuit external to the DAC chassis, and connect via optical links. The DAC can provide the Reference Master clock so the USB port is operated Asynchronous in the correct sense.

Is this problem specific to memory buffers or does it remain with any digital transmission? Is there any particular reason why the little spark of energy that occurs when the incoming bit is read into the buffer will cause more problems than when an incoming bit is received by the usb receiver, or I suppose when optical data is converted to electrical signal?

Only in the fact that greater circuit complexity,the greater radiated energy levels, clocking data into a deep memory buffer means many cells operating at the income data rate, USB requires Memory buffer circuits and communications at the Hosts data rate.... all circuits that are clocked at the Jittery input clock rates.

Is the problem here that if the incoming signal is more jittery there is a greater chance that the second order effect will be damaging. -I wasn't quite clear whether the transmission of this little glitch of energy might be equally problematic whether it was jittery or not. This problem intrigues me because it makes me wonder whether usb might be worse than S/PDIF: would it be transmitted evenly or in more jittery packets than S/PDIF.

Yes exactly this - the greater the input jitter, the greater the noise spectrum components produced, these components will leak into the analogue domain within such a non screen enclosure. We can only attenuate these levels, but never attenuate to zero.

Is it possible that you could alleviate the problem by somehow dithering the input of the data to de-correlate whatever second order effect there was?

Yes, very much so, and the reason the MDAC2 has the advanced clock option where we can eject a controlled amount and spectrum of "Jitter" to de-correlate such effects.

A problem with SPDIF and to a degree USB is a that the "Energy spectrum" of the Data is strongly correlated to the transmitted Audio data. If I where to design the SPDIF interface today (Silicon area is so much cheaper today then when SPDIF was first conceived) I'd scramble the Audio data during transmission to de-correlate such second order effects. This would also greatly help the Clock recovery circuits (PLL's) who have a hard time attenuating these correlated audio data patterns.
 
Status
Not open for further replies.


advertisement


Back
Top