Is Your Media Player Broken?
Director of engineering John Siau wrote, "We have discovered a very serious flaw in iTunes 7.5...[specifically] in the area of 16-bit truncation and/or operating system based sample-rate conversion…. Fortunately the truncation and sample rate conversion problems can be avoided in both Apple and Windows systems. Unfortunately, the iTunes 7.5 bug makes iTunes unsuitable for playback of 44.1kHz CD material. We hope that this bug will be fixed in the near future (details are listed below). There are several players that work flawlessly. Unfortunately, iTunes is no longer one of them! We will be reporting the media player bugs and workarounds on our computer audio wiki pages (www.benchmarkmedia.com/wiki)."
So I called Siau and asked him what Stereophile readers need to know. "The latest version of iTunes for Windows works perfectly for 24-bit word lengths, so Apple has fixed iTunes for Windows and broken iTunes for OSX. Our test computer automatically upgraded itself to version 7.5, so when we looked at test results, we were very surprised by what we were getting. It took us a while to realize that we'd updated and that things weren't like they used to be.
"In terms of music operating systems, we're very much in a state of flux right now. The media player manufacturers are tweaking and changing their designs—and it's a good thing they're making changes. Eventually we'll get to the point where these things are working properly, but there are bound to be some hiccoughs along the way.
"One of the interesting things they've done in iTunes is fix the volume control for the XP version. It's now a 24-bit volume control when the source is 24-bit. What we'd like to see, however, is software that would operate at the sample rate of the audio file, automatically changing sample rates whenever a file with a different one was played. Currently, iTunes only plays at the sample rate specified in the 'QuickTime Preferences' control panel. If you play a file with a different sample rate from the one set in QuickTime, the audio file will be sample-rate converted. The sample-rate conversion in iTunes 7.5 is surprisingly good, but it is an unnecessary DSP process which is best avoided.
"Windows needs to address this, because when the source is 16-bit, the volume control is only 16-bit. We think the length of the volume control should be dictated by the output device and not the input word length. Unfortunately, when you have a 24-bit output device playing a 16-bit Red Book CD, when you adjust the volume control, the word length should increase, but what the Windows volume control does is truncate it back to 16-bits without dither, so the quality immediately goes down unless you use a player with a 24-bit volume control.
"Windows Media Player still does not support playback of 24-bit files without the installation of third party codec plug-ins. We recommend the 'Combined Community Codec Pack.' Once this codec is installed, WMP plays 24-bit files properly. We anticipate that Microsoft will add a 24-bit codec soon.
"At the moment, only Foobar and iTunes for Windows really have 24-bit volume controls. In iTunes for OSX, you've always had to manually set the sample rate, so you can't mix Red Book and high-rez files. The player itself won't adjust from one sample rate to another automatically.
"iTunes 7.5 for OSX still lacks the ability to follow sample-rate changes. We consider this a nuisance for most users and a complete no-go for users that want to play a mixed list of 44.1kHz and 96kHz material. An OSX sample-rate mismatch will invoke the very poor quality sample-rate conversion that is built into OSX. The iTunes 7.5 bug seems to be locking this sample-rate conversion on at all sample-rates other than 96kHz. Until this is fixed, OSX is not the operating system of choice for audio playback.
"The situation is in a state of flux and we're testing and tracking it in our newsletter and on our wiki pages, where our tech support engineer Elias Gwinn will be posting results as we discover them. To get the information in the most timely manner, we recommend Stereophile readers subscribe to our free online newsletter.
"I think we'll see high-quality sample-rate conversion built into the players themselves in the future. We'd rather see no sample-rate conversion, but at least on the Windows side, they've implemented very good sample-rate conversion. On the Mac side, whenever you play a 44.1kHz file [with iTunes 7.5], you end up with a very poor quality sample-rate conversion inserted between the player and the operating system—or else it invokes the operating system's output conversion. We're not actually able to tell which.
"For the moment we're recommending VLC unless you can get an older version of iTunes. Our version of 6.0 tested well, but 7.5 did not. We're not sure where the change occurred—it's not all that simple to dig up older versions of iTunes."
Thanks to John Siau and Benchmark for the heads-up. It's not what we wanted to hear, but it's good to know.