Go Back   Home > Forums > Source & Line > Digital Source

Digital Source Digital Players and Recorders: CD , SACD , Tape, Memory Card, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 4th July 2004, 04:54 AM   #21
lucpes is offline lucpes  Europe
diyAudio Member
 
Join Date: Dec 2003
Location: Iasi
Send a message via Yahoo to lucpes
Quote:
Originally posted by Bernhard
...the dynamics picture, does it show a low level (-67dB) 1 kHz sine ?
Yep, I used lower value gain resistors in the I/V stage than specified by the designer - what I had around - so the voltage out is a tad bit low (7dB lower than the sound card input level - I guess around 1V) but I won't change them now as both measurements and sound (on either CDP transport or soundcard) are spectacular.

I wouldn't pay that much attention to the freq graph, those values do not correlate with the sound quality;

I also guess that the soundcard also uses 24 bit internal for recording no matter what the output bitrate in order to improve the accuracy.

Regarding the DAC itself, I have to close the box, put a lock on it and throw away the key in case I get the tinkering itch - it's a finished item from this POV
__________________
Deep down inside.
  Reply With Quote
Old 4th July 2004, 05:17 AM   #22
lucpes is offline lucpes  Europe
diyAudio Member
 
Join Date: Dec 2003
Location: Iasi
Send a message via Yahoo to lucpes
Quote:
Originally posted by Terry Demol


The AD1892 will impose a digital brickwall filter even when
resampling at 1:1, such is the nature of how ASRC's work.

The idea of 0 x OS is to get rid of brickwall filter.

Cheers,

Terry
Well, I hope I get it right, as far I as I understand it:

The AD1892 is the SPDIF receiver chip, the 1:1 resampling (recklocking) here would be needed to insure that the DAC is not keen at all on source jitter and uses it's own low jitter master clock - I tested this by accident - at first my SPDIF cable had the ground connection broken and the thingie stilll sounded pretty good. I had some reserves too on this, but the AD1892 specs + the very low jitter clock are good enough to ensure that the 1:1 resampling does not degrade the sound at all - see the measurements.

So the AD1892 spits out plain 1x44.1kHz I2S (which should be in 90% of the cases better than directly derived from the incoming jittery SPDIF/TTL signal) to the AD1865 dac; AD1865 I out and the I/V stage have no filtering of their own, just a miller comp cap in the I/V stage to decrease its bandwith to 1-2MHz and prevent self oscillation as the components used here will happily go to around 40Mhz and pick up any RF present in the area.

Hope I did not make any mistakes, I have only a MT degree (Master Tinkerer)
__________________
Deep down inside.
  Reply With Quote
Old 4th July 2004, 06:10 AM   #23
lucpes is offline lucpes  Europe
diyAudio Member
 
Join Date: Dec 2003
Location: Iasi
Send a message via Yahoo to lucpes
Looks like the brickwall filtering appearance on the freq graph is due to the soundcard's ADC conversion, here's the both the soundcard/DAC freq test using RMAA:
Attached Images
File Type: png fr.png (6.3 KB, 357 views)
__________________
Deep down inside.
  Reply With Quote
Old 4th July 2004, 08:44 AM   #24
diyAudio Member
 
Bernhard's Avatar
 
Join Date: Apr 2002
Location: Munich
Quote:
Originally posted by lucpes


Yep, I used lower value gain resistors in the I/V stage than specified by the designer - what I had around - so the voltage out is a tad bit low (7dB lower than the sound card input level - I guess around 1V) but I won't change them now as both measurements and sound (on either CDP transport or soundcard) are spectacular.

The thd graph shows -10 dB input level and the dynamics graph -67 dB input level,

so is it a low level DIGITAL signal in the dynamics graph ?

Or what does the dynamics graph show ?
  Reply With Quote
Old 4th July 2004, 10:13 AM   #25
lucpes is offline lucpes  Europe
diyAudio Member
 
Join Date: Dec 2003
Location: Iasi
Send a message via Yahoo to lucpes
Yep, in the dynamics graph there's a low level digital signal.

THD: 1kHz -3dB 'digital'

dynamics: 1kHz -60dB digital

IMD: -4dB 60Hz and -17dB 7000hz

The DAC's analog out at 0dB digital in is 7dB lower than the 0dB volume of the soundcard's line in, and all the graphs show the soundcard SPDIF->DAC->DAC's (analog) out->soundcard line in chain.
__________________
Deep down inside.
  Reply With Quote
Old 4th July 2004, 10:21 AM   #26
diyAudio Member
 
Bernhard's Avatar
 
Join Date: Apr 2002
Location: Munich
Ok, because Harmonics then start at -50dB which is not so very good.

Is it a "good" dithered signal like the one from Pedja's homepage ?
  Reply With Quote
Old 4th July 2004, 10:49 AM   #27
lucpes is offline lucpes  Europe
diyAudio Member
 
Join Date: Dec 2003
Location: Iasi
Send a message via Yahoo to lucpes
I really don't think that for a -60dB signal a -110dB harmonic is that bad. We're getting into thermal or resistor noise issues in this range, not to mention that I used a $100 soundcard to test with its inherent deficiencies

Here's a PDF regarding some basic concept of measurements for an older version the program used (RMAA 5.3 - http://audio.rightmark.org/). The basic concepts stayed the same, but the frequencies/amplitudes are a bit changed in new version.

Don't know about what you want to say by 'good dithered' signal... I'm not that technical, and I'm not the one who designed the DAC, just a happy customer...
Attached Files
File Type: pdf tests.pdf (63.0 KB, 57 views)
__________________
Deep down inside.
  Reply With Quote
Old 4th July 2004, 06:16 PM   #28
diyAudio Member
 
Bernhard's Avatar
 
Join Date: Apr 2002
Location: Munich
Quote:
Originally posted by lucpes
I really don't think that for a -60dB signal a -110dB harmonic is that bad.

Don't know about what you want to say by 'good dithered' signal... I'm not that technical, and I'm not the one who designed the DAC, just a happy customer...
The -110dB is absolute scale, the signal is -60dB also absolte scale, so harmonics are -50dB.

Just shift the signal to 0 d<B and the harmonics by the same. They will be at -50 dB absolute scale.
  Reply With Quote
Old 4th July 2004, 06:26 PM   #29
lucpes is offline lucpes  Europe
diyAudio Member
 
Join Date: Dec 2003
Location: Iasi
Send a message via Yahoo to lucpes
That's really not true, as you can see in the THD graph (-3dB FS digital sine and resulting noise/harmonics);

There are lots of co-acting factors that result different harmonic spectrae when using 0dB FS or -60dB FS signals on every audio equipment one may wish to test which I won't bother to cover in this particular thread.

Based on your reasoning one would test a piece of equipment with a -90dB FS sine and conclude that a device has only 15dB of dynamic range if the most proeminent harmonic is -105dB FS
__________________
Deep down inside.
  Reply With Quote
Old 4th July 2004, 06:30 PM   #30
diyAudio Member
 
Bernhard's Avatar
 
Join Date: Apr 2002
Location: Munich
We are talking about different things.
DAC distortion gets worse with smaller signals.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Non oversampling cd-94 MK1 D.A.R.R.Y.L. Digital Source 5 1st December 2004 10:33 PM
Non-Oversampling TDA's supra Digital Source 45 24th September 2004 06:56 AM
TDA5141 oversampling or non-oversampling ? Bernhard Digital Source 4 1st September 2004 10:27 AM


New To Site? Need Help?

All times are GMT. The time now is 05:22 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2