DAC and digital volume level mystery - diyAudio
Go Back   Home > Forums > Source & Line > Digital Line Level

Digital Line Level DACs, Digital Crossovers, Equalizers, 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 30th July 2013, 02:15 PM   #1
diyAudio Member
 
hollowman's Avatar
 
Join Date: Jan 2007
Blog Entries: 3
Default DAC and digital volume level mystery

On some DAPs (iPods, etc.) that have both Line Out (LO) and Headphone Out (HO) I've noticed that using variable-level LO (volume), the sound is best about 66% instead of the usually (??) recommended/suggested 100%. The improvement in SQ is significant.
Not sure why sound is best below "0 dB" gain. I've posed this query on a number of forums and have gotten no agreeable response. Is it because lower line-level out forces one to use the receiver/integrated amp's volume pot on higher (more "linear") level? Or is it a combo of factors?
Some have suggested the issue is related to the 2vrms output of CS4398 (or wm8740) used in some of the better DAPs. Here's a direct quote from one responder: "[High performance in] OpAmp LPF [low-pass filter -- this is just the output OPA and its caps] in [a portable, battery-powered DAP] simply cannot be achieved without distortion [at] 2Vrms with limited supply voltage."

The CS4398 has built-in volume. So if you were going to put it in a portable device, what would be its "ideal" Line Out level?

Thanks!!
__________________
"I got banned from a Hi-Fi forum. And I liked it."
- Luv, Katy "Hollowman" Perry
  Reply With Quote
Old 31st July 2013, 04:08 AM   #2
diyAudio Member
 
hollowman's Avatar
 
Join Date: Jan 2007
Blog Entries: 3
Any takers on this query?
A "kit/modder" on another forum literally noted in a PM: " I found a solution and not just going to discuss it with you (especially considering that the answer is more than simple)."
It's curious .... that indiv. is willing to discuss every other part of the project in detail. I'd actually caught the indiv. in a lie ... and you know how that goes ... to save face the string of cover ups progressively gets more and more absurd until your end up with remarks like the above quote.
Hey ... I'll stand corrected ... so that's why I'm posing the query here ...
"Thank you .... thankyouverymuch"
__________________
"I got banned from a Hi-Fi forum. And I liked it."
- Luv, Katy "Hollowman" Perry
  Reply With Quote
Old 31st July 2013, 11:17 AM   #3
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
I don't understand what you are asking. Is sound better or worse at lower digital volumes? You seem to say one then the other.

If worse at lower digital volumes then this could simply be due to losing bit depth at lower volumes. Turn 16-bit audio down by 12dB (a quite small reduction in apparent volume) and you now have 14-bit audio.
  Reply With Quote
Old 31st July 2013, 12:57 PM   #4
diyAudio Member
 
hollowman's Avatar
 
Join Date: Jan 2007
Blog Entries: 3
Default Better at LOWER volume

Quote:
Originally Posted by DF96 View Post
I don't understand what you are asking. Is sound better or worse at lower digital volumes?
Sorry you are confused. Better sound quality at lower volume.
__________________
"I got banned from a Hi-Fi forum. And I liked it."
- Luv, Katy "Hollowman" Perry
  Reply With Quote
Old 31st July 2013, 01:03 PM   #5
Mooly is online now Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Variable level line out might use the class D headphone stage and so be dependant on loading. The headphones often form part of the filter.

Why not try plugging phones in while using LO and seeing if it has any effect.

(Just a guess at a possibility)
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 31st July 2013, 04:00 PM   #6
diyAudio Member
 
hollowman's Avatar
 
Join Date: Jan 2007
Blog Entries: 3
Default Lower DAC digital volume sounds better

Quote:
Originally Posted by Mooly View Post
Variable level line out might use the class D headphone stage and so be dependant on loading. The headphones often form part of the filter.

Why not try plugging phones in while using LO and seeing if it has any effect.
(Just a guess at a possibility)
Thx for your reply.
BOTH the LO (LPF) and HO stages use AD8397 opamps.
The internal config is:
Headphone: CS4398-->LO(LPF)-->HO-->jack
Line level: CS4398-->LO(LPF)-->jack
Where LO is line out stage (with low-pass filter) and HO is headphone amp out.
I have software control over the CS4398's slow/fast DF and vol. control. I also have EQ, but that is done in the main DSP.
Phones + LO simultaneously makes no diff. I have always held the belief that digital vol. decreases bit depth, unless done very carefully (Wadia?). I'm going to assume that lowering the DAP's volume still degrades sound, but MAYBE lower output from the DAC more than makes up for bit-depth loss because other components downstream act more linearly (e.g., output OPA) when the DAC isn't "shouting" at it. And/or my integrated amp's behaves better with lower input signal (e.g., its vol. being operated over entire range -- does an analog pot sound better at the higher end where there is less resistance?)

Oh ... in case anyone cares ... this is one of the DAPs ...
Click the image to open in full size.
Click the image to open in full size.
__________________
"I got banned from a Hi-Fi forum. And I liked it."
- Luv, Katy "Hollowman" Perry
  Reply With Quote
Old 31st July 2013, 07:28 PM   #7
Mooly is online now Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
It was worth a try I guess. No other ideas at the moment I'm afraid.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 31st July 2013, 08:11 PM   #8
diyAudio Member
 
hollowman's Avatar
 
Join Date: Jan 2007
Blog Entries: 3
Quote:
Originally Posted by Mooly View Post
It was worth a try I guess. No other ideas at the moment I'm afraid.
A good guess! ... and stating you don't know ... that's one of the most-respected remarks of all time ... by Socrates:
https://en.wikipedia.org/wiki/I_know...I_know_nothing
__________________
"I got banned from a Hi-Fi forum. And I liked it."
- Luv, Katy "Hollowman" Perry
  Reply With Quote
Old 31st July 2013, 08:27 PM   #9
dmills is offline dmills  United Kingdom
diyAudio Member
 
Join Date: Aug 2008
Location: High Wycombe
Ok, first I need to clear up a somewhat prevalent misunderstanding about digital audio, in a correctly designed system the word length sets how far down the noise floor is, and THAT IS ALL. Critically the system is LINEAR all the way down to (and even below) the noise floor!
This assumes of course that everything is dithered correctly and that the math is done with sufficient precision (Not a given in the portable market).

With a 16 bit system noise floor is 93dB below full scale output for example, and this is independent of the number of bits in use, so turning down by 20dB in the digital domain leaves your noise floor 73 dB below the level corresponding to the input full scale, but of course you can hear right down into it, and the noise remains uncorrelated with the signal.
In a 24 bit system the noise floor is set by the Boltzmann constant (Analogue stage noise always stomps the required dither noise level).

Again, bit depth sets the available dynamic range only, it does not set the 'resolution' (Whatever that means when applied to audio, I have never seen a cognent explanation), and you can hear well down below the LSB in a correctly designed digital system.

Assuming your player is runnig from a single lithium cell (Reasonable guess), the supply rail will be somewhere around 3.5 - 4V or so, so it is quite possible that the issue is running out of headroom in the analogue stages, (for all that that would be poor design), dropping the output 6dB would extablish this easily, as would recording a .wav file containing a clean two tone test pair and doing an FFT of the signal from the lineout while fiddling with the volume.

It is also quite possible that you will find that the digital gain control implementation leaves a lot to be desired, this math is easy to stuff up if you are hard of thinking.

Regards, Dan.
  Reply With Quote
Old 31st July 2013, 08:38 PM   #10
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
What you say is true provided that the digital volume control adds the appropriate amount of dither as the signal level is reduced. The original dither with the signal will be too small in amplitude to deal with quantisation when the volume is turned down.
  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
DAC left channel dropping out. A mystery. Pano Digital Line Level 14 21st August 2011 12:03 PM
set volume level lbstyling Class D 1 28th August 2009 11:12 PM
Very Low Volume Level on DAC impulz2002 Digital Source 8 3rd April 2008 05:41 PM
lesser of two evils, high level -> line level, digital volume control mazurek Solid State 3 19th November 2006 01:25 AM


New To Site? Need Help?

All times are GMT. The time now is 05:37 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