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Sample Rates->Analogue outputs for Mbks and iMacs

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Sample Rates->Analogue outputs for Mbks and iMacs

Postby Jeraldo » Tue May 08, 2012 11:01 pm

When playing files at higher sample rates, say 88.2 and 96K, is that what is coming out of the analogue output? Or is there some internal SRC (reduction) going on for the analogue outs? Is the D/A converter up to the higher sample rates?
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Re: Sample Rates->Analogue outputs for Mbks and iMacs

Postby chris... » Tue May 08, 2012 11:35 pm

Hi,

The audio interface runs at whatever speed is set in Audio/Midi setup.

If you play a file with a different sample rate, the audio will be converted as necessary.

That applies to ANY audio interface - and in the case of the built-in analog output, it's more than sufficiently crap that you don't need to worry about such subtleties.
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Re: Sample Rates->Analogue outputs for Mbks and iMacs

Postby Jeraldo » Wed May 09, 2012 1:12 am

Thanks, Chris.
Perhaps this explains the unusual phenomena I've experienced with certain apps having their own SRC's, often also listed in the "output" section of the software (as opposed to SRC preferences) which can all sound a bit different, ostensibly while no SRC is taking place. But perhaps it is, because of what you've just described.
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Re: Sample Rates->Analogue outputs for Mbks and iMacs

Postby chris... » Wed May 09, 2012 10:48 am

Jeraldo wrote:Thanks, Chris.
Perhaps this explains the unusual phenomena I've experienced with certain apps having their own SRC's, often also listed in the "output" section of the software (as opposed to SRC preferences) which can all sound a bit different, ostensibly while no SRC is taking place. But perhaps it is, because of what you've just described.

Yep - I think you're right. Apps may perform SRC at times, independently of (or in addition to) the OS.

One example is iTunes, which I believe fixates on whatever sample rate the interface is set to *at the time iTunes is launched*. This leads to the following rather less-than-optimal situation:

You start iTunes and happily listen to some 44.1kHz material. Then you decide to listen to a track recorded at 96kHz. So you go to auto/midi setup and switch your high quality sound card to 96, and then hit "play" in iTunes. That may seem correct, but what actually happens is iTunes is still operating at 44.1, so it will convert the data to 44.1, before handing it to the OS. Then, the OS will see the soundcard is operating at 96, so will convert the data back to 96, before sending it to the hardware. So you have two conversions, when you thought you had none :frown:

Of course, this is done in the name of user-friendly operation. Anything can be played by any app at any time. Nothing can accidentally get played at the wrong speed (pitch) etc.

In the above example, a solution is to quit-and-relaunch iTunes AFTER changing the sample-rate in audio/midi setup. At least, if you remember! Sadly there's no indication whether stuff is set right or not (ie. what sample-rate iTunes is using).

There are alternate player apps which do not do any SRC, and claim to be 100% bit-transparent. I sometimes use Audirvana. But none of this is likely to be relevant if using the crappy built-in audio ;)
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