16 Bit vs. 24 Bit for Mac OSX

Can a Mac, or specifically an IMac, be configured for 16bit 44.1khz via USB?

I've an IMac 20 that I'm using with a Benchmark DAC1. I've noticed the following -

When opening up the Midi/Audio Interface Application and selecting "Built in Input" and setting it to 16/44.1, it appears it's sending 16/44.1 to my DAC. I'm well familiar with the sound of 16/44.1 compared to 24/44.1 from my experience with my PC using Foobar, and the sound appears to be 16 bit coming from the IMac. When I select the Benchmark Dac1 under "Output Device Settings" in the Midi, the IMac then appears to revert to 24/44.1, as is set under the output device options.

My curiousity is that the Midi setting is for "Built in Input" not output. Further, the output settings are still 24/44.1 with the Benchmark as the default output device, I've only selected the Input settings options to change them. Am I confusing anything here? When the input settings are chosen, no output settings are listed at all within the menu, so there's nothing to alter there unless I go back to the pulldown menu and select the output device again.

Sorry if I'm not explaining this well, but basically I've found 16/44.1 to be preferrable for redbook lossless. I'm not a big fan of the extra sound stage and bloom that 24/44.1 offers over the original 16bit source material as it's recorded.

Steve (Audioengr), if you catch this post, you suggested setting Output on the Mac to 24/44.1 for true bit perfect. But when I select Input device and set it to 16/44.1, it definitely sounds like 16 bit and to my ears appears to be bit perfect as well.
Benchmark have a wiki page on this - have you checked there? 16 bit or 24 bit should make no difference in sound (just adds eight 0's)UNLESS you are using digital volume control or digital EQ (quite likely)- in this case how the software handles the bits and the number of bit can be very important - especially at low volumes - more bits is more accurate and it is also important to dither after digital attentuation.

There are also a number of bugs with iTunes - so check carefully which version is acceptable. PC audio is a bit of a minefield.
You need focus on the "output" device. That's what matters, and has to do with the usb dac, as you're concerned with here. Forget about all the input stuff - doesn't apply. A usb dac is an output device.

When you make a selection in the MIDI screen, the screen changes for selection of the settings for that device selected. The Benchmark in this case.

Basically, when you plug in a usb device, such as a usb dac, it reports what it is capable of doing, e.g., 16 or 24 bit, or, 44.1 or 96 kHz. This then populates the selection found for that output device in the MIDI screen, that you may then select from.

In other words, what you see there is what you're capable of doing.

No mine field, pretty simple.
To the first post, 24 bit and 16 bit make a difference. It did on my laptop using foobar and changing the foobar setting from 16 to 24 and back. It's subtle, but it's a definite difference in soundstage presentation (24 bit providing a wider, more blended soundstage.

To the second post, I completely understand the the selection of devices with regards to output. My question surrounds the INPUT device selection and it's ramifications on the OUTPUT stream. Let me put it this way, when the Audio Midi "Properties For" is set to "Output Device, Benchmark Dac1", it puts out 24/44.1. Further, the DAC1 WILL NOT go into sleep mode when the computer is put to sleep (and at times it won't sleep when the computer is turned off). Now, when the Audio Midi "Properties For" is set to "Internal Input Device" and you change the settings to 16/44.1, the Dac1 responds with a different sound which to me is for all appearances 16/44.1, and further, the DAC1 will go into sleep mode when the computer is put to sleep. Also, there are no "properties for" settings for output when you select the built-in input settings.

The crux of this is I believe Macs are set to both receive and put through digital streams. I wonder if the Mac is locking it's usb output to 16/44.1 when you select that for input, as the two are communicating to one another. To me, it sounds bit perfect.

And again, there is a difference between 24/44.1 and 16/44.1. A definite difference. And it sounds incredibly clean with no distortion, so I'm inclined to believe both are bit perfect.

I've looked for info all over regarding this, but there's not much out there regarding interaction with Audio Midi and DACs, even on the benchmark website (they seem to contradict themselves depending on what version of Itunes you use, which is understandeable given the changes from version to version).

To the two prior posts, I do appreciate your input, sorry if I seemed dismissive, but there's a definitive difference between the 16 bit and 24 bit settings, almost as if it's putting the DAC1 into NOS mode.


To the first post, 24 bit and 16 bit make a difference. It did on my laptop using foobar and changing the foobar setting from 16 to 24 and back.

If the original data is redbook and this makes a difference then it is likely digital volume control or digital EQ or some other manipulation which is making an audble difference. A software bug is a possiblity too.
It's redbook data. But both software (Itunes and Foobar) have the ability to convert to 24 bit before sending to the DAC. I'm fairly certain it's not volume control or any EQ settings, though I am exercising ITunes volume control when using the IPod Touch as a remote control. ITunes version 8's volume control works perfectly, as has been confirmed with both Benchmark and Steve Nugent.

There's a review of the Bryston BDA-1 DAC which has an upsample bypass to put out 16/44.1 and bypass the onboard upsampling. The reviewers comments are within the link below, but he hits the nail on the head by describing the difference between 16 and 24 bit upsample (from redbook) as a broader soundstage. Same thing I've encountered with the DAC1 when feeding 16 bit, although I've no way to tell if it's locking in at 16 bit or if it's upsampling on the DAC before final output.

I agree with Mr. Ultrafitimes, forget about input settings, they have nothing to do with this. Input settings matter if you are feeding a signal into the computer. You are not so these settings are irrelevant.

You are correct that you can only choose to view either input or output properties in Audio Midi Setup at one time, but that doesn't mean that you have no output when you select input or that the input settings affect the output. It is confusing because when you select input properties the output is grayed out and it says "output is not supported." I don't know why they did that but it only means you can't change settings for the output unless you select properties for output.
If 24 bits is 16 bits with 8 extra zeros then there should be NO difference as there is no additional information. Something else in the software must be causing the difference. FWIW - as a general rule it is best to always use 24 bit s- this helps minimize processing errors from digital volume control and EQ.
Just be aware that, whenever you change the output setting in Audio MIDI, you have to reboot iTunes for it to take effect. This is because iTunes checks the Audio Midi setting when it boots up and continues to use that setting until you reboot it.

If you fail to reboot iTunes after changing the Audio Midi output setting, I have read that you may end up going through two sample rate conversions, which can degrade the sound quality. Keep this in mind when you are evaluating the sound from different settings.