[OZZIOZZI]

I have a mixture of audio files in iTunes on a MacMini mid-2007 Core 2 Duo 1 GB RAM, 1.83 MHz currently running OS X 10.5.8.  I use it primarily for music, ripping CDs to Apple Lossless. I also download both 256k MP3 Freegal albums, courtesy of my local public library membership, plus some 24/192 high-definition music from various websites and some WAV and AIFF files.

 I believe that iTunes does not change the sample rate it uses for playback of these various files. Is that correct? In MIDI settings  I have the digital output settings at 96kHz 24bit 2ch as this is the highest it will go.
This matches SOME of the files I have been playing. My question is WHY does the playback of 24/192 and even 24/384 files sound better than 24/96 ones and certainly much better than 256k MP3 s? Does iTunes upsample and downsample to match the 24/96 output settings?

I plan to upgrade MacMini soon to 3GB RAM and OSX 10.7 and run music from an external Firewire drive. I would also like to run BitPerfect as I have read that this does automatic file rate selection track-by-track. Would this solve my problems. PS is my Mini capable of running 10.7 in 3GB RAM older version of BP for 10.6 is no longer available from the App ;-(

[dB Cooper]

I don't feel like I have enough tech chops to address this but I notice no-one else has chimed in... you might wanna try over at Computer Audiophile.

[Bemopti123]

I think that the reason why you are hearing improvements from higher bit sampled stuff perhaps has to do with the fact that you are aware you are playing formats at a higher resolution?  Also, what I am not really clear is the upsampling that is done by DACs, of smaller files.  The smaller files have smaller bits of information that upsampling processors must be interpolating in order to make a virtual copy of this lower resolution file?  That is how I assume things are reproduced because what bits are missing originally, can only be recreated but are not really there.  It is interesting to see whether the improvement of sound that you perceive is real or more an effect of suggestion.   

[avta]

I'm no expert but as far as I know iTunes will play the files up to the setting you have put in the Audio Midi utility. I do it think it will up sample anything. MP3 files are lossy meaning that a portion of the originally recorded file is missing. Lossless files such as AIFF or Flac files, for example are lossless i.e. all the original information is present. Many people think lossless files sound better as do higher resolution files. This is still an area of debate however. Much depends on the system used for playback particularly the dac. Hope this helps.

[Mike Nomad]

You will be limited by the capabilities of the hardware. Upgrading the software will not get you over that hurdle. Example: My MacBook Pro is a late-2011 model. Running 10.11.3, I still can't do any better than 24/96 on the output.

I haven't used iTunes in quite a while, so, I can't speak authoritatively as to what goes on with hi-res file playback.

[Jonathon Janusz]

If you are running a version of itunes higher than 11.0.2 (if I remember right), there are separate sampling rate controls for playback in itunes beyond those in midi setup.  Midi setup will set the sample rate that the OS will want to use (via core audio) and the mac will try to send everything out at that rate.  If you have a version of itunes as noted above, you can also set itunes to upsample the audio from there, then pass it to the OS in midi setup, potentially having the audio resampled a second time if say you started at 16/44, had itunes spit it out 24/192, then have the OS dial it back to 24/96.  If the native output of your file matches the setting - either in itunes or in midi setup - it will pass unchanged.  Note depending on these settings, you can also get high res files to downsample (say 24/192 down to 16/44) before going out.

TL:DR match the settings in itunes and midi setup to whatever the file is you're playing to have everything pass through unchanged.  Anything else will change the output in some way (up or down depending).

The reason the highest you can go is 24/96 is probably because you are using the analog output on the mini.  If your software versions support higher rates, if you switch to the optical out or go to an external DAC that supports it, you can get 24/192 natively out of the mini.

Why changing the settings for different files (up or down sampling depending) sounds better?  Around here, you'll probably find that to be a big personal preference thing, but as long as you're getting better sound that makes you happier, go for it. 

The MP3s are a different story when discussing these things, as the other file types mentioned do not make the same kinds or extent of changes to the original music file that MP3 compression (regardless of bit rate) does, which adds another layer of complexity (compression plus sample rate vs. just changes in sample rate).  Again, if you can upsample the MP3s and get better sound, have at it. 

Unless you are trying to explicitly stay as true to the source as possible, whatever you adjust to taste is just that and as in all things with this hobby totally cool if it makes you happy. 

[OZZIOZZI]

In answer to some of your questions, I am outputting music via TOSLINK Optical and the DAC I am using has maximum rates of 24/96 with USB input and 24/192 with optical input. Since I am using optical out I tried to set digital out from the Mini to 24/192, but OS x Midi setup only allows 24/96 as the maximum available output ( this doesn't agree with the idea that the output settings reflect what is plugged into the digital out of the mini. ) I suspect confusion reigns in most Apple users because Apple makes this information difficult to find so as to support their plug-n-play philosophy. I'm not complaining, just trying to set up various interfaces so they are at their optimum settings. Until I hear a really straightforward explanation of Apple file handling, I might just leave things as they are as they seem OK. BTW I am listening some of t he time through AKG headphones and can certainly hear the difference between 256k MQP3 s and 24/192k downloaded music files. I am not imagining that difference, but original recording and mastering quality far overtakes bit and sample rate considerations in my opinion.

After reading the computer audiophile forums I believe most of their recommendations are " Upgrade your Mac Mini to the latest model, install 16GB RAM, use PUre Music+ or Amarra Pro, get a power conditioner, custom power cords and interconnects and cryo treat the entire system to make it superconducting, oh yeah, and don't forget the gold-plated connectors and silver wire in every cable." I exagerate, but not much.  Thanks for all the suggestions. Hopefully someone from Apple or an apple tech will read this thread and enlighten us all.

[Crimson]

Even though Apple states that their optical output supports up to 24/192, I have only been able to get a max of 24/96. I typically use USB anyway, which does not have this limitation.

As to up-sampling and such, Core Audio will up/down-sample all files to the settings in AudioMidi Setup regardless of the file's native format. This can be worked around by using third party audio playback software such as Audirvana, Amarra, Pure Music, etc., which also have the added benefit of automatically switching to the file's native bit and sample rate.

[Mike Nomad]

~

[Johnny2Bad]

Audio Midi Setup ("AMS") is the key application for selecting MacOS Audio output (and input).

iTunes does no resampling; in fact technically speaking iTunes does nothing except organize files and acts as a portal to Apple online services.

All iTunes audio functions are performed by QuickTime via low level functions in the OS (Core Audio).

AMS controls the operation of the Digital Audio chipset (the hardware) built into the Mini. Core Audio (all OSX Macs of a reasonable version, I believe OSX 10.4x and higher, but don't quote me on that) operates natively in 32-bit floating point, so in every case audio is converted from that sample rate to whatever the software or user demands.

Note that there need be no actual resampling in the sense the audio data is altered; the conversion from 32 bit floating to 24 or 16 bit simply involves throwing away zero's that "pad" the data. They are added to convert, say, a 24 bit file to 32 bits by adding 8 bits of zeros, going back to native involves throwing away the added 8 bits of zeros.

Since that chipset (built-in hardware in your Mini) is capable of 32 bit (float) at 96 Khz encoding or decoding, that is your maximum option in Audio Midi Setup with your particular machine.

If you select a different sample rate than the native file in AMS, then that will be the sample rate the ADC or DAC operates at. In other words, it will resample the data (up or down) if the file and the selected sampling rate are not identical.

Since your hardware is not capable of 192 Khz native operation, all 24/192 files will be resampled to whatever you set output in AMS to (eg 24/96).

However iTunes (and by definition QuickTime, and also Core Audio) can deal with files greater than 24/96 (greater than 24/192 for that matter).

So, if for example you use a DAC that replaces the built-in 24/96 chipset (perhaps a USB DAC, for example), then you can play back higher resolution files natively; the software can deal with them no problem.

I recommend setting AMS to 24/96 (or 24/88.2 as you see fit) and leaving it there if you are using the built-in DAC in your Mini. If you are using another DAC via USB, Firewire, or Optical output from your Mini, then you are free to set AMS to a higher playback resolution.

Note that higher resolution will show up as an option in AMS as soon as you connect a DAC that is capable of higher resolution. If your external DAC is not connected, then AMS will show the highest resolution the built-in DAC is capable of (24/96 in your case).

Hope that helps.

RE: 24(32)/192 via Optical Out ... I am fairly unfamiliar with the Optical interface, having really never used it. I would think that if it is capable of 192Khz then there must be 1) a native 24/192 file available and selected for playback; 2) a DAC connected via Optical S/PDIF that is 24/192 capable, and 3) some sort of handshake, perhaps even a driver, so the system knows what we are asking of it. I have always assumed the S/PDIF out was 24/96 only, but like I said, never really looked at it much.

[Jonathon Janusz]

Looking at Preferences in iTunes 12.3.2... not seeing anything of the sort.

Sorry... I must have been half asleep this morning and got my wires crossed thinking about both the mac and windows versions of itunes.  itunes 11 for windows has those bitrate control drop down menus.  Johnny2Bad did a lot better job than I did in explaining how the guts work on the mac side.

Regarding tossing the mini and buying a newer/bigger/better one, as I've had two minis running in front of me for a few weeks trying to finally decommission the old one (for regular work use, not just as a music server), I have had a chance to compare the old one (OS 10.4.11, itunes 9.2.1(4)), to the new one (OS 10.9.5, itunes 11.x?) and also on the new one (OS 10.9.5, audirvana 2.3?).  Each of these setups has some minor sound quality inspired OS tweaks but nothing too extreme. 

I can say that for me, itunes 11 sounded clearly the worst of the three.  Surprisingly, the main thing itunes 9 gave up to audirvana was some clarity and detail; otherwise, for me the heart and soul of the music so to speak were just fine and I could be happy with the sound from itunes 9.  Please do keep in mind that my current rig is kind of pieced together and not even close to optimized for detail, more going after tone and compromising on some of the other audiophile check boxes.

If it were me and I already had the mini, I'd buy a 10.6.8 CD from Apple for I think about $30, get the system set up and tweaked with OS optimizations, and enjoy.  You'll have a darn good source component for not a lot of money.  Add or change up DACs as you fancy and it should be able to keep up with you fine for quite a while.

[Johnny2Bad]

I agree with Jonathan. I see no need to spend money on a new Mini when the one you have is perfectly fine for the job at hand.

Max out your RAM (cheap these days, and an absolute must, in my opinion), get a SSD if you want (or wait, the 1 TB units will be available at a reasonable cost, maybe sub-$300, within a year in my estimation, and that holds a lot of HiRez audio. 512 is just a little small for my audio storage use).

Get a MiniStack external drive from Other World Computing (OWC) ... they are awesome and you can, if you want, get one with a Blu-Ray player or burner, plus an external drive, plus plenty of true additional (powered) expansion buses. If you don't want an optical drive (HD only), they are inexpensive.

However OWC also has the option to add a HD or SSD and remove (in place of) your optical drive in the Mini. Which is why I want to make sure you are aware of the optical drive options in the MiniStack. Naturally there is nothing stopping you from using any generic external optical drive you might want to pick up from a PC vendor, at a low price.

Make use of "About This Mac" and be sure to check so that you hook up your kb/mouse and HD or other external drive onto distinct USB buses. Or your idea of using Firewire for your music storage drive is excellent, as FW is an autonomous (self-managing) interface and does not need any intervention by the CPU to operate (unlike USB).

For an OS on a machine that is not internet-exposed I like 10.8x, but again you are free to choose here. If you expose your machine to the 'net, then you need to think about replacing it with one that can run a newer, supported version of the OS to maintain a reasonable level of security.

Unplug it from the outside world, and you can do whatever you want in safety. If you have another computer, you can expose that one, and use a FW or Ethernet cable to transfer data you download to the basic audio-only machine.

Unlike WindowsOS machines, you don't need to dedicate your Mini to audio to insure proper performance, but since it is a bit long in the tooth you may as well run it dedicated so your RAM in particular can do it's job on audio. A 2007 model will have limited RAM capacity, that is why I suggest an older OS version and not exposing it to the internet. But I see no need to spend money on a new machine or retire this one, it's more than up to the job you require of it.

Some Links:
Current Mini: (HD and SSD variants)
http://eshop.macsales.com/shop/ministack/
2009 and Older Mini: (one example, bare enclosure)
http://eshop.macsales.com/item/NewerTech/MSCKIT0GBSW/
MiniStack w/Optical Drive (one example, there are other options)
http://eshop.macsales.com/item/NewerTech/MSMXBW3.0TB7/
OWC DataDoubler (add a second HD or SSD to your Mini, for backup or RAID)
http://eshop.macsales.com/shop/internal_storage/Data_Doubler

[OZZIOZZI]

Thank you for all your replies ESPECIALLY THE ONES COVERING HOW ITunes and OS X handles audio files.  I have already ordered a MiniStack external HD enclosure. I already have an externl USB Superdrive that I use mainly as CD/DVD drive on a MacBook Air when travelling. I have been ripping CDs on internal Combo drive of MacMini. I ordered the MiniStack because it sits exactly under the MacMini and can cionnect via Firewire. I have noticed a time lag occasionally when clicking on a track in iTunes. I am hoping the Firewire interface will transfer files faster than USB, especially if I use a faster HD externally. I have also ordered a RAM upgrade at the same time as the MiniStack (1+2 GB) rather than the original 1GB (512 + 512MB). That might improve the audio performance from what I have read on this Circle. I already turn off all other Apps and other things that might make demnds on processor or memory. Funny thing though is that I have never noticed audio quality issues even when I am using Safari, TextEdit, WiFi and Bluetooth, despite the dire warnings on some audiophile sites. But I do believe that the less functions running the better POTENTIAL improvements in audio file handling, up- or down-sampling and other OS X operations that require processor and memory demands. The one thing I always remember is that even the  basic level mid-2007 mini can handle HD video playback.

My take away from the previous posts. Set AMS to highest displayed bit depth and sample rate, in my case 24/96 (which I have already been using) and OSX /Core Audio will take care of up and down sampling. Use Firewire to external HD audio files. Connect to external DAC via optical, mainly for resistance to EMI RFI. To DAC. I already use external, linear, regulated 12V and 5V power supplies for the external HD and DAC, hopefully to lower the noise floor in DC.  I'm not sure this is completely necessary, but is easy to implement DIY.

The one question I have left is whether it is worth upgrading the OS to 10.7 so I can run BitPerfect, mainly for the auto switching of sample rate out to the DAC. Any comments on this would be appreciated. I can tell when anything better than a 256 K MP3 is playing, but the distinction between Apple Lossless and higher definition files is a bit harder to pick.

Thanks again for all the comments and suggestions above.