MacOS Midi settings question

[Bob Stern]

2 serious shortcomings of iTunes handling of different sample rates:

 

#1:  Suppose you launch iTunes while Audio MIDI happens to be set to sample rate A.  Suppose you then desire to play a track whose sample rate is B.  You diligently change Audio MIDI to sample rate B to avoid unnecessary upsampling.  iTunes will resample the track from B to A, then Core Audio will resample the resulting audio from A to B.

 

#2:  Core Audio's sample rate conversion algorithm has different quality levels that can be specified by an application.  The lower quality algorithms are offered because they are faster, ie, impose less CPU load.  When iTunes does sample rate conversion, it never uses the highest quality algorithm.

 

Both behaviors were confirmed by Apple audio engineer Stephen Davis on Sept 12, 2009 on the "CoreAudio-API" discussion list hosted by Apple for developers of audio applications.  Davis said Apple engineers had known of bug #1 in at least iTunes versions 7, 8 and 9 but were not authorized to devote any effort to implement a fix.  I don't know for sure whether anything has changed in the ensuing nine years, but there is no reason to be confident that it has.

[jhwalker]

5 hours ago, Bob Stern said:

2 serious shortcomings of iTunes handling of different sample rates:

 

#1:  Suppose you launch iTunes while Audio MIDI happens to be set to sample rate A.  Suppose you then desire to play a track whose sample rate is B.  You diligently change Audio MIDI to sample rate B to avoid unnecessary upsampling.  iTunes will resample the track from B to A, then Core Audio will resample the resulting audio from A to B.

 

#2:  Core Audio's sample rate conversion algorithm has different quality levels that can be specified by an application.  The lower quality algorithms are offered because they are faster, ie, impose less CPU load.  When iTunes does sample rate conversion, it never uses the highest quality algorithm.

 

Both behaviors were confirmed by Apple audio engineer Stephen Davis on Sept 12, 2009 on the "CoreAudio-API" discussion list hosted by Apple for developers of audio applications.  Davis said Apple engineers had known of bug #1 in at least iTunes versions 7, 8 and 9 but were not authorized to devote any effort to implement a fix.  I don't know for sure whether anything has changed in the ensuing nine years, but there is no reason to be confident that it has.

 

Scenario #1 no longer exists, at least in the current version of iTunes / macOS I'm using (iTunes 12.9.x and macOS Mojave beta 6).  That is, iTunes does not "retain" the sample rate set in Audio MIDI at the time of launch, it uses whatever is CURRENTLY selected in Audio MIDI.

 

Note that you can still select the "wrong" setting in Audio MIDI and it will be output at that rate (e.g., a 96k file output at 44.1k) and there is still no support for auto rate changes.

[Bob Stern]

2 hours ago, jhwalker said:

Scenario #1 no longer exists, at least in the current version of iTunes / macOS I'm using (iTunes 12.9.x and macOS Mojave beta 6).  That is, iTunes does not "retain" the sample rate set in Audio MIDI at the time of launch, it uses whatever is CURRENTLY selected in Audio MIDI.

 

How did you determine that?

 

The 2-step conversion to a "historical" sample rate and then to the rate currently set in Audio MIDI is not indicated in the user interface.