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audiomidi upsampling


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hi- quick question: i altered the audio midi setting on my mini to 24/96. when playing itunes at 16/44 loss less and upsampling, the sound is of higher quality (for me): more 'air' and generally stronger midrange - just increased clarity of vocals. will altering audio midi 'actually' produce these changes?

thanks.

 

johnnyturbo

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A couple of things. First, the default setting in Audio MIDI Setup is 24 (not 16)/44. Older versions of iTunes did operate at 16-bit, which meant that you were only getting a bit-perfect output if you kept the volume at 100%. By going to 24-bit, Apple provides enough space so that any recalculations required by a decrease in volume can be sufficiently accurate.

 

As for using 96 Hz -- think of an HDTV. When provided with the proper signal (1080p), the picture is fabulous. Provided with something less (480p, from an old DVD), and the picture is considerably less. Basically, that 480p is being converted into 1080p format -- the 480p information is just being spread over the terrain designed to accommodate the 1080p signal. It's not being improved, which is what upsampling should do. The problem here is that the 16/44 standard is that old DVD.

 

But some TVs (or DVD players) do have really good upsamplers. The DVD will look much better than its original resolution, but not as good as a true 1080p signal. That's because the upsampler is making a lot of calculations -- based on the 480p signal -- to determine what it thinks a 1080p version of that same signal would look like.

 

Pure Music has a pretty good upsampler. By the way, most (but not all) people think that any upsampling should be done on an integer basis (meaning you can double the original signal, but don't multiply by something odd like 1.22 -- this way you can retain the original information and add to it, instead of replacing the entire package).

 

Gordon Rankin has some helpful thoughts on this at http://www.usbdacs.com/Macintosh/Macintosh.html.

 

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It looks like you already have the best setup for upsampling. Audio MIDI has a relatively crude upsampler. To avoid using it, set Audio Midi to the highest sample rate that your DAC can receive from the Mac. In most cases that is 24/96.

 

When Itunes launches, and only when it launches, it checks the Audio MIDI settings and adjust itself accordingly. If iTunes sees 24/96 in Audio MIDI as it's launching, then from then on iTunes will upsample 16/44.1 or downsample 24/192 as it plays your music. 24/96 audio files would be transferred out unaltered, or bit perfect.

 

iTunes has a decent upsampler built in and that is probably what you are hearing. Also, always keep the iTunes volume at maximum.

 

More detail is described here;

 

http://www.benchmarkmedia.com/wiki/index.php/ITunes-QuickTime_for_Mac_-_Setup_Guide

 

CD

 

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