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  #676  
Old 06-09-15, 02:35 PM
JohnW JohnW is offline
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I've also got a "Jitter Bug" for test - but as far as I can tell (looking at the USB Eye pattern) it offers very little filtering on the USB datalines themselves - I suspect its more about filtering the USB power.

Can someone point me to the Paul Miller review as I seem to recall he measured risetimes around 15nS to 20nS which is very slow (must be USB 1.1) - maybe I'm recalling incorrectly...
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  #677  
Old 06-09-15, 02:38 PM
JohnW JohnW is offline
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Quote:
Originally Posted by jamjar784 View Post
John, that seems encouraging. If you listen to any of your favourite test tracks do you hear any benefit to SQ with the Regen and MDAC 1 or whatever you have available?
I'll have to setup a decent system with my ESL's when I'm ready for the listening tests

It well take a little time to get used to the new "System" setup in the lab
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  #678  
Old 06-09-15, 02:47 PM
jkeny jkeny is offline
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I believe there may well be a common mode filter on the D+/D- in the Jitterbug

I don't think Paul Miller's review is on-line but some graphs & data has been posted in forums http://www.whatsbestforum.com/showth...l=1#post336508

This image is a composite overlay of the with/without eye pattern plots & yet the apparent "reduction" in jitter is stated to be from 22nS to 16nS - yes this was done with a USB device running at FS - the Audioquest Dragonfly (note this is also powered from Vbus). Also there is some speculation that PM reversed the jitter figures & that the jitterbug increased the jitter value as would seem to be correct from the plot & what looks like the action of a LPF

  #679  
Old 06-09-15, 02:47 PM
jamjar784 jamjar784 is offline
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Quote:
Originally Posted by JohnW View Post
I've also got a "Jitter Bug" for test - but as far as I can tell (looking at the USB Eye pattern) it offers very little filtering on the USB datalines themselves - I suspect its more about filtering the USB power.

Can someone point me to the Paul Miller review as I seem to recall he measured risetimes around 15nS to 20nS which is very slow (must be USB 1.1) - maybe I'm recalling incorrectly...
Someone has posted some screenshots from the article here http://www.whatsbestforum.com/showth...ements/page20&
  #680  
Old 06-09-15, 03:01 PM
adamdea adamdea is offline
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Quote:
Originally Posted by jamjar784 View Post
Someone has posted some screenshots from the article here http://www.whatsbestforum.com/showth...ements/page20&
the measuremnt is supposedly 14.77ns with jitterbug and 21.96 without
As you can see from those plots, which I referred to last week, the changes look more like a degradation (as you would expect from a low pass filter). The overlay which JK linked to shows it best. The supposedly improved risetime makes no sense other than as a technical measurement anomaly (at best). Pretty much what I expect from Paul Miller since he started printing rubbish about flac files being congested compared with WAV

Last edited by adamdea; 06-09-15 at 03:35 PM.
  #681  
Old 06-09-15, 03:22 PM
misterdog misterdog is offline
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Quote:
Originally Posted by radamel View Post
Who said anything about focusing purely on CPU speed?
My wrong, all digital is based on 0/1 so all must be equal, and perfect.
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  #682  
Old 06-09-15, 04:16 PM
rtrt rtrt is offline
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Hi John do you plan to continue with the MDAC mix of both XLR and RCA output connectivity? Ive found it useful, though I do appreciate that converter cables are available
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  #683  
Old 06-09-15, 05:01 PM
BE718 BE718 is offline
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Quote:
Originally Posted by radamel View Post
Yes. It was perhaps underpowered but not anymore.

OTOH I also tried an overpowered i7 with pretty dismal results.
Then with respect you are doing something wrong or have some problem with your setup.
  #684  
Old 06-09-15, 05:06 PM
BE718 BE718 is offline
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Quote:
Originally Posted by radamel View Post
I think Keith misses a lot in most things he talks about not only the fine details unfortunately.

I do think you are the one missing the fine details.

I never said it was because of faster or slower CPUs.

Simply that a PC with a fast CPU can have pretty dismal results and one with a slow CPU can work very well if its OS is properly tweaked.
So why do , probably literally millions of people use untweaked PCs without issue? I dont think its the computer with the problem.....
  #685  
Old 06-09-15, 05:12 PM
BE718 BE718 is offline
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Quote:
Originally Posted by JohnW View Post
OK, as I expected the USB HUB does "repackage" the data and remove huge amount of the Host PC's USB Packet jitter - I can no longer see the vast amount of Process related jitter on the scope, its all much cleaner.

The edges of the waveforms still display a "Fuzzyness" which is indicative of jitter - but atleast its not an unholy mess of the direct PC connection.

I see the Regens biggest advantage is removing a lot of the "differences is sound quality" between software players and computers (With Bit Accurate Data).

I'll now have to use a more advance test step up to analyse the jitter as now the jitter is at a more acceptable level - I was worried with my first tests (USB Direct to the PC) as it was such a mess.
Great stuff John,

So my question is what is happening in the MDAC when it receives the data.

Can you explain the process - does the decoded audio data end up in a buffer and clocked out locally? So is the USB packet jitter causing effects through modulating supplies, ground planes etc?
  #686  
Old 06-09-15, 05:19 PM
JohnW JohnW is offline
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Quote:
Originally Posted by rtrt View Post
Hi John do you plan to continue with the MDAC mix of both XLR and RCA output connectivity? Ive found it useful, though I do appreciate that converter cables are available
Yes the RCA output will still be available, but without the Current Sense feedback obviously
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  #687  
Old 06-09-15, 06:23 PM
JohnW JohnW is offline
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The Analogue scope measurements of the USB direct and ReGen USB revealed the truly "horrid" nature of the USB traffic from a PC with heavy "CPU Process" jitter modulation - and I've been trying to think how to graphically capture it so I can post it here on PFM.

So I dug up a Digital scope - rearranged the lab to make space for it... I think its the first time I've really used it - I hate them, but it proved useful to capture the data.

https://dl.dropboxusercontent.com/u/...rect%20usb.jpg

Above is a colour graded eye pattern of the Direct PC USB connection to an XMOS based DAC (streaming 1KHz, 0dB FS) High speed USB.

Note the multitude of lines, but more importantly that the background is not black (Black means no data points fell in this area) - the background its dark blue because during the acquisition low frequency "Runt" waveforms where sampled in this area - these "Runt"waveforms occurred as the PC / operating system processed other applications / Operating system house keeping tasks etc. On the Analogue scope it was a horrific mess...

https://dl.dropboxusercontent.com/u/...egen%20usb.jpg

Now with the ReGen USB Data, notice not only the much cleaner waveform but far more importantly that there is very little "Runt" data - the background is Black. The USB Hub IC in the Regen has for the most part cleanly repackaged the data.

The colour grade data sample hit size is the same for both plots (20K Hits on the Red).
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  #688  
Old 06-09-15, 06:31 PM
JohnW JohnW is offline
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Quote:
Originally Posted by BE718 View Post
Can you explain the process - does the decoded audio data end up in a buffer and clocked out locally? So is the USB packet jitter causing effects through modulating supplies, ground planes etc?
Yes, I strongly believe that the USB Packet jitter cause "second order" effects in the MDAC (PSU, Ground plane and RF modulation).

I realise that the MDAC's USB device (the TAS1020B) not only decodes the USB, but its also the house keeping processor on the MDAC mainboard - so its directly connected to the ESS DAC (via the ESS's I2C MCU configuration port) allowing multiple RF coupling paths between the external USB Host device (PC / Computer) and the ESS DAC.
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Last edited by JohnW; 07-09-15 at 03:43 AM.
  #689  
Old 06-09-15, 10:56 PM
sbgk sbgk is offline
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Quote:
Originally Posted by JohnW View Post
OK, as I expected the USB HUB does "repackage" the data and remove huge amount of the Host PC's USB Packet jitter - I can no longer see the vast amount of Process related jitter on the scope, its all much cleaner.

The edges of the waveforms still display a "Fuzzyness" which is indicative of jitter - but atleast its not an unholy mess of the direct PC connection.

I see the Regens biggest advantage is removing a lot of the "differences is sound quality" between software players and computers (With Bit Accurate Data).

I'll now have to use a more advance test step up to analyse the jitter as now the jitter is at a more acceptable level - I was worried with my first tests (USB Direct to the PC) as it was such a mess.
bit of an assumption to say that software players and computers affect sound quality, my objectivist friends say that sound engineering principles and measurements says that they all sound the same and no dbt has proven otherwise. All very confusing, especially as I do hear differences.
  #690  
Old 06-09-15, 11:06 PM
avole avole is offline
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All of which explains why wireless or optical is the way to go. Oh, and why there's no difference between USB cables, which can't act as filters.
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