Audio Artefacts in Windows 7

[General notes]

This is an attempt to summarise and clarify where I am with Windows 7 audio playback in relation to Audition and some general audio applications.

Most tests were carried out using an M-Audio Fast Track usb interface on a machine running Windows 7 64-bit, having an on-board Realtek soundcard. All Windows sounds and audio effects were turned off, but note that "Enhancements" in Windows Control panel has a tick box called "Disable all Sound effects" which does not disable sound effects, but disables the scroll bar that allows all the effects to be seen and disabled.

General notes

Windows 7 normally resamples all audio to whatever is set as the "Default Sample Rate". If the default matches the actual sampling rate of the file, resampling does not take place.

The Realtek Control panel appears to have precedence over the Windows 7 Sound Control Panel in terms of setting default sample rate.  They usually, but not always, remain in step.

The Windows Control Panel has to be closed and re-opened to be sure it is showing the sample rate in use as the default by Windows.

If the M-Audio device is enabled (although not being used) in the Windows Control Panel Recording tab (NB this relates to the WDM function of the driver), switching sample rates when using the asio driver results in an error message about unsupported sample rates. A Tascam usb device does not give the error message.

For testing, I generated  50Hz tone files modulated by 45Hz with a modulation frequency of 0.1Hz and of 30 seconds duration, one at 44.1kHz sampling rate, one at 48kHz. Sweep tones could be used, but this gives a more obvious effect.


Audition 1.5 using the M-Audio interface

Doesn't appear to set Windows default sample rate to the sample rate of the file.

If the default sample rate in Windows or the m-audio control panel and the sample rate in the file do not match, aliasing occurs.

The same effects are observed when using the Realtek audio.


Audition 3

Using asio drivers with the M-Audio appears always to set default to sample rate of file. Files play correctly and sample rate switched to match appropriate file

Using AA Windows Sound drivers doesn't set sample rate to the rate of the file. If the default sample rate is set incorrectly, there are loud crackles from about 10 seconds into the file but not obvious aliasing. With the correct sample rates, the audio is clean.


Winamp can be set to alternative audio output drivers. It aliases when set to use Wave Out, but not when set to Direct Sound.

Windows Media Player v. 12 appears to play cleanly whatever the sample rate settings are in Win 7.

YouTube videos played through Flash Player plugins to FireFox or IE show aliasing distortion if the sample rate is not set to match correctly. Files on YouTube seem to be mainly 44.1 or 22.05 kHz.

These effects may be rare unless one is working with audio with different sample rates, but it is quite possible for the Windows Sample Rate to be altered by an application without it being noticed.

I am still seeing the different problems with the AMD-based machine with usb 1.1 audio interfaces and still seeing effects when switching between tabs on the Windows Control Panel audio area.

So really you need a good audio interface with proper ASIO drivers in order to guarantee your audio quality with Win 7. So anything that doesn't have them ie. on board chips, is likely to be messed up by the OS. Which, I suppose, also means that AA 1.5 can be gravely disadvantaged by Win 7.

Does ASIO4All help at all or is it likely to be affected by Win 7 regardless?

I think the point is that you need to be certain you are using a version of Audition that uses asio drivers and that version has to be using them rather than the wdm drivers with your high quality interface.

So with AA 1.5 under Win 7 you have to take a great deal of care.

Also, if you are using something like "Stereo Mix" as a source for recording, you have to be very careful.

I have actually got asio4all on a Win 7 machine and will test it, but I believe it will act like the Audition Windows Sound driver.

One of the reasons for the delay in writing this up was that I couldn't understand why I was getting crackles (which I've described elsewhere as like a machine gun sound) rather than the aliasing when using AA3 with Windows Sound. I still don't, but it became a case of "Publish and be damned".

I've done a little more work on this without any glaring breakthroughs.

Asio4all seems to behave pretty well and hasn't produced any significant glitching or aliasing. I don't normally use asio4all, though, so this may not be a very thorough test.

I've also made a test DVD using Vegas 10. I had some awful results initially, which, I believe, were because I set up a project to record a DVD with the parameters set up by the initial Vegas installation. This sets the audio to 44.1kHz. Having imported my 48kHz files, and then checked the project properties, I changed the sample rate to 48kHz. This seems to have produced audio that had changed rate twice and sounded dreadful.
Then I started a project and set the audio to 48kHz 16-bit and burnt a DVD. The DVD plays without any noticeable aliasing whatever the sample rate in Win 7 is set to, but the audio within Vegas is affected, aliasing when Win7 is set to 44.1kHz.

Vegas doesn't appear to alter the default Win 7 sample rate (and so it can distort) and playing a DVD doesn't change any settings within Win 7. This last was the thing I wanted to check most to make sure that playing a DVD would not interfere with basic audio settings.

I think it is worth just posting this cut and paste which summarises Microsoft's current (10th August 2011) position pretty succinctly.

The statement was posted in a Microsoft forum, by a Microsoft employee in the test section of the Windows development team, in direct response to a question about aliasing occurring when using the sample rate converters in Windows 7. Sample rate conversion is very likely to take place in Windows systems without most users being aware of it.

" I confirm that this is a known bug, but I cannot give any updates at this time; in particular I cannot make any statements regarding a patch. "

I've done a wipe & reload of Windows 7 Starter Edition (using the Recovery Media), and then inspected the sample rate of the integrated Realtek HD audio interface. It is 48kHz.  This is what I suspected, because I didn't think I had changed the settings before I heard the problem in YouTube.  (I get the impression most YouTube content is encoded at 44.1kHz. Certainly, when I attempted to upload a 48kHz clip, it was converted to 44.1kHz)   
Note that I can reproduce the problem with the standalone "projector" Adobe FLASH player as well. I have not tested any non-YouTube sites that use FLASH but I assume they'll behave the same.

Microsoft's stated policy is that the default sample rate was initially set to 48kHz in Vista and this was changed in Windows 7 to be 44.1kHz.We now have your machine that fails to follow this, and I have my recently purchased Thinkpad that, on its first boot, set record and playback to different sample rates.

Yes, YouTube seems to be mostly 44.1kHz. I know the person who banged away before me and got Microsoft to admit there was a problem found examples of the same videos on different sites as well as YouTube and had examples where they played cleanly from one site but not another.

I now think the biggest issue with this, and the one that is the most difficult to work around, is the way that, as referred to in my initial posting, an application that uses asio with an audio interface that is described as "multi-client" (eg some M-Audio usb devices) behaves. Set the sample rate in asio in Audition 3, and the default MME sample rate in Windows for the same device follows and may change the default Windows sample rate without you knowing. This may only matter if you work with both types of driver, but unfortunately this is exactly how many of the people that I know do work - with a laptop, an audio interface and more than one audio application. It is very easy to end up with warning messages from various sources and/or glitching or distortion on both record and playback.

I don't know what the real answer is. I think Microsoft started out with good intentions, but didn't consider the implications of things like this, jack sensing etc. for those of us involved in professional or creative audio. 

What Windows 8 needs is an audio button that sets all the sample rates and disables any automatic switching.