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Should I buy a digital interface?

post #1 of 10
5/28/11 at 4:11pm
Thread Starter 

I have an NFB-12 dac/amp and plan on using it with a MacBook pro or other laptop via USB. My understanding is digital interfaces are recommended when you have a relatively poor source, such as a laptop.

 

Should I use a digital interface with my laptop? Does it make a big difference?

 

Any thoughts/experiences would be helpful.

 

FYI: will be playing lossless 16- and 24-bit music files

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post #2 of 10
5/28/11 at 4:18pm
Quote:
Originally Posted by movi View Post
Should I use a digital interface with my laptop? Does it make a big difference?

 

For me, it made a very big difference. I'm also using a MacBook Pro playing hi-res FLAC and lossless files. Read up on the various models currently available.

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post #3 of 10
5/28/11 at 5:49pm

The MacBook Pro does not have a line level analog output, and it is true that the amplification provided by the MacBook Pro's headphone out is nothing to write home about. Hence the need for an external DAC (which does provide a line level out) if you want to use a headphone amp with your MacBook Pro.

 

The positive is that your MacBook Pro includes an optical out (which shares the headphone out port); you access it using a TOSLINK adapter like this one:

TOSLINK adapter for MacBook Pro

 

and this (with a TOSLINK cable) can go straight into a receiver for up to 96 kHz/24 bit playback. And that is pretty cool for leveraging any stereo systems in your home; it is less cool when shopping for a mobile or desktop DAC as those are mostly USB only . . . and MacBook Pros aren't exactly overflowing with USB ports.


Edited by MtnSloth - 5/28/11 at 5:56pm
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post #4 of 10
5/29/11 at 5:44am
You already own the NFB-12, right? You should use its DAC rather than the headphone out of the laptop. There's nothing else to buy apart from a USB or optical cable.
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post #5 of 10
5/29/11 at 11:21am

The MacBook Pro (and most/all iMacs) has a combination headphone and optical out. If you plug-in an 3.5mm (1/8 inch) stereo cable, you are getting amplified analog stereo out; and the DAC in your MacBook Pro is in play. However, if you use the optical out, you are not using the DAC in the Mac - it is a true optical out.

 

If a DAC accepts optical in, as the NFB-12 does, that is probably the way to go for both theoretical as well as practical reasons. If you have better than 96 kHz/24 bit audio files, why not take advantage of the higher potential resolution of the optical interface (192 KHz/24 bit)? Not particularly persuasive to me, but it may be to others. The more practical point in favor of using the optical out on the Mac is the relatively paltry number of USB ports on MacBook Pro - why lay claim to a potentially scarce resource if you don't need to?

 

PC notebook computers? Yeah. You are probably stuck with the USB interface on the NFB-12.

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post #6 of 10
5/31/11 at 5:20pm
Thread Starter 

thanks for the replies.

 

to clarify: i own an NFB-12, which is a DAC/amp and has USB, Optical, and Coax inputs.

 

my understanding was that using a USB-to-Coax digital interface (such as the popular HiFace units) will be an upgrade over simply plugging a USB cable into the MB Pro and connecting it to the DAC/amp that way. is that correct?

 

I wasn't aware that the headphone out in the MB Pro has an integrated optical out. so now the question arises, which is better:

 

1. to use the optical out and send the signal untouched to the NFB-12? or

2. to use the USB out with a digital interface, allowing both the MB Pro's soundcard and the digital interface to affect the sound?

 

and lastly, if I use bit-perfect audio AKA kernel streaming, wouldn't I be able to leave the MB Pro's soundcard out of the equation and send the signal directly through the USB connector? or does kernel streaming simply prevent any software from interacting with the sound (like the k-mixer in windows)?

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post #7 of 10
5/31/11 at 7:35pm
That's not how the audio architecture of OS X works. (If you're really curious, take a look at the docs.)

With optical or USB, the Mac's sound card isn't messing with the bits at all--the DAC in the NFB-12 becomes the sound card.*

One advantage of optical is that it electrically decouples the DAC from the computer, so you eliminate any incidental noise (fan, power, etc.) the USB copper might carry. In practice, it probably won't make an audible difference on a Macbook.

Adding a media converter (or "digital interface") to the chain would be transparent at best.

Get an optical and a USB cable, and let your own ears be the judge....

* The one thing to be mindful of is that you don't want OS X settings to mis-match the bit depth of the audio files. You can check this in Audio MIDI Setup. If the bit depth is set higher, it should just pad-out with zeros, so that shouldn't be a problem unless you run into latency issues. If it's set lower than the bit rate of the audio file, however, your output would no longer be bit perfect. And, needless to say, you shouldn't touch a software EQ if you're concerned about bit perfect output.
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post #8 of 10
6/1/11 at 7:22pm
Thread Starter 
Quote:
Originally Posted by wilyodysseus View Post

Adding a media converter (or "digital interface") to the chain would be transparent at best.


interesting. so why is it that, for example Audio-GD markets their digital interface as being for upgrading a poor source. and many people have reported good results using usb-to-coax digital interfaces like the HiFace when used on laptops. i understand your other points but this one i'm still confused on.

 

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post #9 of 10
6/1/11 at 8:05pm
Quote:
many people have reported good results using usb-to-coax digital interfaces like the HiFace when used on laptops. i understand your other points but this one i'm still confused on.
As am I.

I could make a few guesses, but I'd love it if someone could explain how the hiFace audibly improves output. The conversion to and from optical involves some overhead, for example, but the chain would need to be flawed in some serious way for that to cause an audible problem in most cases.

This is not to say that I'm calling devices like the hiFace hokum. They're very useful as media converters, if that's what you need. I actually considered the hiFace myself because of the physical fragility of the optical connector/adapter in Mac's headphone out port. And being an OS X and Linux guy, maybe I'm unfamiliar with some Windows audio problem solved by the hiFace.

EDIT: I poked around the m2tech website a bit, and read the one short whitepaper. Looks like this device might be more useful with Windows or if you actually have some 192kHz source files (or files with a sample rate that otherwise exceeds the maximum output of your built-in interface). The jitter claims made by the paper are so extraordinary, however, that I'm pretty turned-off by the company.
Quote:
"In standard environmental conditions [...] a change of nearly 10kHz is not uncommon. We think we’re listening to the right sampling frequency, but actually we listen to a different sampling frequency and all instruments are 'out of tune'."
I would be very surprised if jitter could cause an audible 10kHz frequency shift under typical real-world conditions, which seems to be what they're claiming. Maybe I'm misreading this, though.

EDIT AGAIN: Obviously they're talking about 10kHz variance out of the 192kHz sampling frequency, not 10kHz variance in the audible output, which would be ridiculous. But I'm still skeptical that a human would be able to distinguish such a variance at 192, to say nothing of 44.1. Hopefully one of the sound science guys can jump in here and give an answer as to whether a typical computer sound card drifts that much in the real world....
Edited by wilyodysseus - 6/2/11 at 3:20am
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post #10 of 10
6/2/11 at 8:44am
Thread Starter 

i don't know. i wish there was more clarity on these topics.

 

do any of these issues exist with a high-quality CDP source? i get the feeling there's all this mucking around when you want to use a computer as a source, because computers have never really been intended to be a high-quality digital audio source. so you sort of have to strong-arm a computer to get it to do what you want for outputting music, what with jitter, and bit-perfect setup in the software, and digital interfaces, and signal isolation. it's all to prevent the computer from interfering with the audio stream.

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