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Oct

29

An Overview of Windows Sound and Music “Glitching” Issues

Category: Vista News | Leave a Comment

The following post comes from my colleague Steve Ball, Senior Program Manager for Sound in Windows Vista, and continues his team’s on-going series on how Windows Vista treats various forms of audio.


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Part I: Why does my Windows sound sometimes “glitch?”


Windows is a rich and complex OS designed for multi-tasking users whose tasks must share access to scarce system hardware and resources.  Unfortunately, despite multiple decades of incredible advances in PC and CPU architectures, there are non-trivial, complex interactions between applications, processes, and devices in even the most advanced personal computers that make a supposedly “easy” task — like playing back music without occasional glitches — much more difficult than it may seem at first glance.


Another way of thinking about this:  it seems odd that a modern >$2000 PC may sometimes have trouble seamlessly playing back music when $20 CD players can effortlessly playback music without glitches. 


So why do many $2000 PCs occasionally glitch while playing back music?  The quick answer is this:  Windows is not a single-function device like a CD player.


A slightly longer answer goes like this:  even an average Windows machine today is commonly used simultaneously as a media player, word processor, presentation projector, spreadsheet number cruncher, authoring tool, photo editor, media server, video recorder, music composition tool, communications device, search engine, virus detector, data compressor and decompressor, and backup manager.  And these are only a few of the possible tasks and processes that are run at the same time on the hundreds of millions of Windows machines that are in use today.  Each of these tasks or processes, in isolation, would hardly tax the resources of modern PC hardware.  But in our multi-tasking world, unavoidable resource conflicts do sometimes occur between the huge and diverse ecosystem of Windows hardware that enables these tasks.  Even on the most expensive, brand-new machine, occasional glitches can occur if and when the system attempts to divide its finite resources among these multiple, diverse, independent, power-hungry activities.


What is a glitch?


A glitch is a perceivable error, gap or pop in the sound caused by discontinuities in the audio signal during playback or recording which result from processing or timing problems.  Glitches during music playback can sound like a loud “pop” or like a brief slice of silence randomly inserted where your music should have been.  Some customers have also described what “glitching” in their own words as:



For the purpose of this discussion, let’s lump all of these descriptions together under one general class of problems and call these “glitching.”  While a glitch that happens during music playback can be annoying and unsettling, a glitch that occurs while you are recording or communicating with someone can result in frustrating and unacceptable data loss.


What causes my Windows sound and music to glitch?


Digital media processing is time-sensitive.  Playback requires specific work to be performed by a given deadline — otherwise presentation or data loss can occur.  A “glitch” occurs when a deadline for time-sensitive processing is missed or when time-sensitive data is lost.


For example, in Windows Vista, playing back music involves “work” that must be done at least every 10 milliseconds so that there can be a continuous stream of music out to your speakers.  The “simple” task of playing back music consists of the following steps, all of which must be completed before a strict deadline:



  1. a small chunk of data from a music file needs to be read from a disc (CD or hard drive)

  2. this data needs to be “decompressed” or “decoded” (usually in system memory) so it can be streamed out to your speakers in a format that your sound hardware understands

  3. the decompressed sound data needs to be copied from system memory to your sound hardware memory

  4. the data in your sound hardware needs to be sent to your speakers at the appropriate time

  5. repeat steps 1-4 flawlessly every 10 milliseconds (ms)

In this example, if any of these steps aren’t completed on time, then the user could hear a glitch in the music playback.


Elliot Omiya, Architect on the Sound dev team, puts this 10ms cycle into perspective:  “it’s just slightly longer than the time it takes a nerve impulse to travel from the end of your finger to your brain (~8ms), known as NCV (nerve conduction velocity).  Because synapses are like network switches, there is switching time involved before the nerve impulse gets to the brain, i.e., switching time adds to latency.”


There is some good news in this story:  Windows developers have made significant progress over the years in reducing glitching across key multimedia scenarios.  For example, music playback on an otherwise “lightly loaded” system can be generally as smooth as that $20 CD player.


But because of the multi-tasking nature of Windows and the vast array of new and legacy hardware in the ~1B PCs that are used to playback music today, this allegedly simple process is made more complex by the resource sharing that occurs between applications and hardware.  For example, it is not uncommon for certain older devices driver to occasionally “lock out” the CPU for 10-50ms, thereby causing obvious audio glitches.  This is just one example of the kinds of complex hardware, driver, and OS interactions that can cause glitches.


In summary, some of the common sources of glitches today include:



My colleague on the Windows Sound team, Larry Osterman, also pointed out to me recently that humans are actually “hard-wired” to be disturbed by audio glitches.  In an exchange about this topic, Larry observed that audio glitches are more obvious than video glitches because the ear’s tuned to notice high frequency transients — his visceral example of this idea is an image of a stick snapping in the woods behind you as an audio event that wakes you up before a bear wanders into your path. 


In my second post on this topic, I’ll go a bit deeper in sharing details of work we’ve done in Windows Vista to address some of the known sources of potential sound glitches, including some additional background about a recent discovery of an apparent connection between multimedia playback and network throughput.


I wish to acknowledge the contributions and suggestions from my colleagues Hakon Strande, Richard Fricks, Alex Ferreira, Lan Ye, Larry Osterman and Elliot Omiya for this series of posts.

Oct

25

Visiting the Windows Consumer Experience Space in New York City

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In New York City this week, Microsoft has invited over 200 members of the press to visit the Windows Consumer Experience Space at Peter White Studios. There, they will get hands on demos of scenarios that both Windows Vista and Windows Live together enable for consumers. The scenarios at the Windows Consumer Experience Space include demos of the Windows Live apps (such as Windows Live Mail and Windows Live Photo Gallery), gaming on Windows Vista, and Windows Media Center and its home entertainment capabilities.

Windows Senior Product Manager Craig Cincotta gives us a tour of the Windows Consumer Experience Space where folks will come through for their demos:



Video: Windows Consumer Experience Space Walk-thru


One of the scenarios being demoed is the ability to create panoramic shots in Windows Live Photo Gallery. I absolutely love this feature and decided to go down to Times Square and take a few shots to create a panoramic view of Times Square during both during the evening and during the day. It is an amazing experience standing at Times Square especially at night with all the neon signs and I wanted to share that experience through the panoramic shots.


Times Square (Night) Panoramic Stitch


Times Square (Day) Panoramic Stitch 


In creating a panoramic shot, another scenario is being able to use Windows Live Photo Gallery to upload and share that photo to either Windows Live Spaces or Flickr. I chose to upload the panoramic shot of Times Square to my Flickr account and embed it in this blog post - however the same scenario also works if I uploaded the image to Windows Live Spaces as well. For an excellent overview of uploading photos to Flickr through Windows Live Photo Gallery, check out Program Manager Michael Palermiti’s screencast and blog post.


Several of our Featured Communities were also invited to visit the Windows Consumer Experience Space such as Blair Briggs, Michael Reyes, Bob Stein, John Obeto, Patrick Husband and Jason Dunn.


In celebration of the Windows Consumer Experience Space - Microsoft has also launched Windows Vista Holiday Product Guide in which users can download to get the low-down on all the excellent new products (which are Certified for Windows Vista) hitting the market this holiday season that take advantage of Windows Vista such as the Gateway One and the Dell XPS 720.


 


There are many awesome consumer scenarios both Windows Vista and Windows Live can offer and we will continue to blog about them here on the Windows Experience Blog. Be sure to subscribe to the Windows Experience Blog’s RSS feed since not all blog posts hit the frontpage of the Windows Vista Team Blog. 

Oct

23

Partners helping fix Vista Software Compatibility Issues

Category: Vista News | Leave a Comment

When chatting with people about the deployment of Windows Vista within their organisation, one of the topics that comes up is software compatibility.  It’s a no brainer that their business applications continue to work whilst they are enjoying the benefits and features of Windows Vista.  Microsoft have worked hard to ensure  we had a large number of software vendors ready to offer their software as “Certified for Windows Vista” or “Works with Windows Vista“.  These certifications mean that either software is designed specifically to take advantage of new features in Windows Vista or is compatible with Windows Vista.


Whilst these certifications go along way to answer questions about software compatibility, there are still bespoke software solutions or legacy applications that might not have been tested by Microsoft to gain the certification.  For businesses in this situation there are a range of tools that will help test the compatibility of applications on Windows Vista.  Microsoft provide a great toolset, for instance, called the Application Compatibility Toolkit which is worth checking out for the analysis of your software portfolio.


Our partners have also taken the initiative when it comes to application compatibility testing and fixing of issues.  ChangeBase, a company based in London, England have recently launched their new software “AOK” which analyses applications and then fixes any issues that might cause problems, leaving you with the green light to get on with your deployment.  They recently published a press release highlighting the great work they have been doing with AstraZeneca who have roughly 70,000 desktops across 60 countries.  You can find out more information about ChangeBase and the application compatiblity software at their website.

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