Audiokarma.org
Audiokarma Featured Sponsor

Go Back   AudioKarma.org Home Audio Stereo Discussion Forums > Digital Formats & Music Server Forums


We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 09-01-2012, 08:14 PM
tppc's Avatar
tppc tppc is offline
Dogs know best
 
Join Date: Jul 2011
Location: SE Mich
Posts: 568
Bit-perfect playback using iTunes and Windows 7 - almost

If your favorite audio player is iTunes you probably already know that it can only interface to the Windows 7 audio stack using Shared mode which passes audio samples through the Windows Audio Engine (mixer). Itunes does not yet offer a setting to enable Exclusive mode which passes audio samples unaltered (bit-perfect) directly to the audio device bypassing the Windows Audio Engine and any digital signal processing (DSP) that the engine may perform.

You can however achieve "near" bit-perfect playback using Shared mode by making a few simple changes to Windows 7 sound settings, and being mindfull of where volume control occurs and of any DSP that may occur in the audio device.

The Windows settings are accessed through tabs on the Control Panel Sound applet for the given default audio device.

1. Set level to 100%
2. Disable sound effects
3. Set output sample rate = source sample rate
4. Set output bit depth > source bit depth

With these settings the Windows Audio Engine will only perform int->float(32)->dither->int processing on the audio samples. There will be no Windows volume or effects processing, no sample rate conversion, and since the output bit depth is greater than the source bit depth, mathematical precision is maintained and truncation distortion is avoided when the float(32) samples are dithered then converted to the output integer bit depth.

The only DSP that occurs in the audio engine is dithering. It's actually re-dithering since the samples would have already been dithered at some point during audio post production. This gets as close to bit-perfect through the audio engine as is possible using Shared mode

But what about volume control?

Since Windows volume level for the audio device is set to 100% that leaves volume control in the hands of either the audio player or an external device such as a Preamp or DAC. Since the goal is to maintain near bit-perfect playback (i.e., the only DSP is dither) then the volume control must not perform any DSP on the audio samples.

The only case where no volume DSP will occur is where the audio player volume is set to 100% and an external analog volume control is used. If however the audio player controls volume or the external device uses a digital volume control then DSP occurs on the audio samples.

Finally, the device driver and firmware for the audio device (external DAC, motherboard audio chip, sound card, etc) must not perform any DSP on the samples before converting them to analog.

Chat w/whiteboard on the Windows audio stack from two of the designers: Larry Osterman and Elliot Omiya.
http://channel9.msdn.com/Shows/Going...-Stack-and-API

BACKGROUND: WASAPI Audio Rendering Modes

Note: all existing Windows audio API's were re-plumbed to go through WASAPI.

Shared mode: audio is processed by the Windows Audio Engine before being sent to the hardware audio device. The audio engine performs DSP including mixing, enhancement (EQ, bass boost, etc.), sample rate conversion, dithering, and so on. Multiple audio applications can send audio simultaneously through the engine and share the hardware audio device, hense the term "Shared mode".

Exclusive mode: audio bypasses the audio engine and is sent directly to the hardware audio device. When an audio application enables Exclusive mode, no other application can use the audio device. Exclusive mode is geared for pro-audio applications that perform their own DSP, however it can also be used to achieve bit-perfect playback if (1) the audio player does not perform any DSP and (2) the hardware audio device supports the source sample rate and bit depth exactly and does not perform any DSP before converting the samples to analog.
__________________
DSP done right makes the music sound better
MacBook Air | RPi (Airplay) + ODAC | Yamaha HS Series
Reply With Quote
  #2  
Old 09-03-2012, 03:11 PM
satkinsn's Avatar
satkinsn satkinsn is offline
low end audio
 
Join Date: Apr 2010
Location: Watertown NY
Posts: 1,818
Do you know if the audio stack has changed in Win 8?

s.
__________________
"I liked the murmur of the announcers, the sounds of those voices speaking calmly from thousands of miles away." - Teju Cole
Reply With Quote
  #3  
Old 09-03-2012, 05:05 PM
tppc's Avatar
tppc tppc is offline
Dogs know best
 
Join Date: Jul 2011
Location: SE Mich
Posts: 568
Quote:
Originally Posted by satkinsn View Post
Do you know if the audio stack has changed in Win 8?

s.
I have not done much digging yet but I would guess that most of the changes in the 8 audio stack are probably along the lines of bug fixes and algorithm improvements. The 7 stack is pretty nice as-is from my experience and I can't envision any major redesign happening. Hopefully though there will be some new audio features in 8 that will benefit Hi-Fi.
__________________
DSP done right makes the music sound better
MacBook Air | RPi (Airplay) + ODAC | Yamaha HS Series
Reply With Quote
  #4  
Old 09-06-2012, 02:31 PM
tppc's Avatar
tppc tppc is offline
Dogs know best
 
Join Date: Jul 2011
Location: SE Mich
Posts: 568
This article provides a pretty good overview of the media subsystem in Windows 8.

http://blogs.msdn.com/b/b8/archive/2...-platform.aspx
__________________
DSP done right makes the music sound better
MacBook Air | RPi (Airplay) + ODAC | Yamaha HS Series
Reply With Quote
  #5  
Old 09-06-2012, 06:18 PM
satkinsn's Avatar
satkinsn satkinsn is offline
low end audio
 
Join Date: Apr 2010
Location: Watertown NY
Posts: 1,818
Thanks.

s.
__________________
"I liked the murmur of the announcers, the sounds of those voices speaking calmly from thousands of miles away." - Teju Cole
Reply With Quote
Audiokarma
Reply


Thread Tools
Display Modes

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

Forum Jump


All times are GMT -5. The time now is 02:20 AM.



Friends of Audiokarma
We appreciate your help in keeping this site going.
Black Swamp Audio
Organ Donor Parts
Sonneteer
 
Sound Stage Direct
Parts Connexion
AudioClassics
Atlantic Systems
AV Solutions
Take Five Audio
Tone Arm Audio
Audio Salon
Musical Paradise
Audience AV
Classic Sound Repair
Simply Speakers
McIntosh Cabinets
BD Enterprise
Cabledyne
Howard Products
BOI Audio Works
FM DX Antenna
Amplifiedparts
Siliconray
RSL Speakers
Vinyl Magic Record Cleaner
Salk Sound
Grant Fidelity
Urban Antigue Radio
Yesterday's Audio
Many Moons Audio
DeWick Repairs
The Tube Store
Vintage Electronics Repair
Audio Doctor
Politicalchat.org
MCM Electronics
Antique Radio Classifieds
Herbies Audio Lab
Videokarma.org
   
Powered by vBulletin® Version 3.8.6
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
ęCopyright 2002-2014 AudioKarma.org, All rights reserved.