iMac Sound Quality

Has anyone compare an iMac using it's optical digital output to feed an external DAC, to other PC based alternatives like the SB2/3 or USB SPDIF converters?
I have an Apple Powerbook G4, which I've used to feed a Musical Fidelity Trivista DAC 21 through the optical out on an Apple Airport Express. The sound quality was better than the sound quality directly through the analog out on the Airport, but it never lived up to all the magical reviews I've read about the DAC 21. I never hooked the DAC 21 up to a CD transport to find out whether the limiting factor was the DAC or the Apple Airport Express optical out, but I'll bet it was the Airport. Recently, I purchased a Scott Nixon USB Tube DAC, and hooked it up to the USB connection on my Powerbook. I've been very pleased with the results, which are much better than my experience using the Airport/DAC 21. If your iMac is close enough to the stereo to use a USB DAC, I would recommend it. I'm using a 15' USB cable, and it works fine.

Hope you find this helpful.

Mark- Thanks for the feedback. I'm hoping the iMac's digital output connection is better than the wireless Airport Express or the SB3's digital output.
I'm not positive about this but, in general, I think you are better off when you use the USB out than a other out's.
"I'm not positive about this but, in general, I think you are better off when you use the USB out than a other out's."

Pardales- the USB output is powered by the PC's PSU and will transmit it's noise to the USB converter/DAC. The iMac's digital output is fiber, so the PC's PSU noise is isolated from the DAC.

Of course there's the issue of which output has lower jitter.
Better off with USB output for sound. First off, just because something is fiber does NOT mean it is the better choice. In this case if your goal is to isolate then yes you can use the optical connection. But...USB is a bi-directional connection, so timing errors are dealt with on the way in and on the way out. Not the case with your optical. Doesn't mean jitter is eliminated, don't know there is a connection that does that yet, but it is certainly better for sound quality.

If you want the best of both worlds, isolation and sound quality, you can simply use an Optical USB cable. One called Opticis is one that has been successfully used but people who want to isolate and use USB. Altough the PS on the Opticis has been called into question in the past, most people who have used it speak hightly of it.

I can say, from experience that I use a Kimber USB on my system from a MAC, and it is as quiet as a church mouse, and dynamic peaks come from BLACK backgrounds. So for me personally, isolation is not worth it.
At the high end, the best solutions have been USB converters that reclock the signal at a high level of accuracy to eliminate jitter, such as the Empirical Audio Freeway or Off-Ramp, or the Wavelength Brick or Cosecant. Also at the high end are networked devices, such as the Slim Devices Transporter, which uses the ethernet to pass the signal from the computer to the DAC. If you are at the high end, it is easy to find a good solution.

Since my budget does not currently allow me to be at the high end when it comes to getting the signal from my computer, I have the same question that you have. I am running audio from USB to an M-Audio Audiophile USB and then running S/PDIF to a fully tweaked-out MF X-DACv3. I get a large sound stage, great dynamics and an overall musical presentation, but insruments could be better defined and the sound could be smoother, as is evident in comparison to my ModWright Sony 999ES. The problem is prior to the DAC, because it goes away when I connect the Sony to the DAC with a glass Toslink (i.e., using the Sony as a transport).

I have been reading a lot of posts and I can share what I have learned so far:

1. There is a huge difference between TosLink cables. The good ones use a large number (say, 128) of glass (not plastic) fibers and highly polished glass lenses. There is an Audiogon member who sells goods ones at a very reasonable price. Just search for "glass Toslink". The bad ones have helped to give optical cables a bad reputation, although according to Gordon Rankin at Wavelength, there were also problems with the early optical transmitters and receivers.

2. The optical connection on the iMac (which I have) requires a mini-Toslink adapter and I have not been able to find any that say that they are made of glass fibers, with highly polished lenses, as opposed to cheap plastic. This leads me to suspect that they are cheap plastic. I haven't been able to find any information on how much of a difference this makes, given the short length of the adapters.

3. If you need to do a long run of the Toslink cable (say, over 3 feet), it is recommended that you use an extender to boost the signal. Specifics on the quality of these extenders is also hard to find (glass or plastic innards?).

4. Posts that compare direct Toslink optical to the use of a USB/digital converter are hard to interpret if they don't indicate whether or not they used a quality glass cable for the comparison.

5. There are many posts that give extremely high marks to the Trends Audio UD-10, which can be had for about $130. It can run off of USB bus power, but will sound better with the optional battery-powered power supply. But many say that it works best with an external 5 volt, 1.5 amp linear, non-switching power supply, which is the same power supply used on the Squeezebox 3, which power supply you would have to buy separately from a company such as Digikey. For even better results, will modify the power supplies. There are many threads on the Trends unit on

6. The HAGSUSB as also received some favorable reviews. It can be purchased already assembled or as a half-kit.

7. For use as a USB to S/PDIF converter, some have said that comparison tests show that the Trends is better than an unmodified Squeezebox 3. Others, however, have said that the Squeezebox 3, modified by, is better by far.

7. At least on the Mac, the built-in USB audio drivers are high quality and are said to be better than the proprietary drivers of some USB/SPDIF converters. One post indicated that, on a Mac, both M-Audio's Audiophile USB and Edirol's UA-5, using their special drivers, were inferior to the Edirol unit running off of Apple's built-in USB audio drivers. Unfortuately, the Audiophile USB cannot be used without its special driver.

8. If you are using a converter that runs without the installation of special drivers, it is reported that you can use the Audio MIDI (in the Utilities folder of your Mac) to turn on software-based upsampling -- useful if your DAC does not upsample and your converter permits an upsampled signal to be passed to the DAC. Since my converter requires a special driver, I have not been able to test this.

I may have run on a bit long, but perhaps you can benefit from my research over the past week or so, with a bit of a Mac persective. I am also waiting for a definitive answer to the questions, "What is the best moderately-priced USB/S/PDIF converter for use with the Mac?" and "How does that compare with a direct optical connection from the iMac to the DAC?"


Thanks for your reply.

My son just a MacBook, so I hope to test it's optical output
using a Monster Cable ICable.

If you look at my system, you'll see I'm using a modified SB3 with a linear psu.



PS- On the subject of glass verses plastic Toslinks, see:

Thanks for the link on the plastic cables. It is good to hear that they now come with higher purity/transparency materials.

You may find this link interesting:

I would like to hear about your experience with the MacBook's optical out.


Thanks for the impactacoustics link. On the plastic vs. glass Toslink issue, I guess it's a question of who do you believe, the company selling 1M glass cables for $60. or the one selling 1M plastic cables for $9.

Listened to the MacBook last night using a 2M Monster Cable ICable. Ripped a WAV file of Keith Jarrett's "My foolish Heart" Live at Montreux for testing.

IMO, the Macbook's digital sounds much better than a stock SB3's digital outputs. I haven't used a Apple computer, so I need to play around some more with settings and try Apple Lossless, but I'm very impressed.
ALAC is better with the MAC since you probably won't get the metadata without, particularly with WAV.

Toslink is better because it isolates, but thats really it's only advantage. So it seperates the noise from one device to the next.

MACs are particularly quiet machines anyway. My question is when did the Macbook start shipping with a Optical out? I thought only the Macbook PRO had that?

The WAV files captured all the information I need.

Unlike you and your tube DAC, I've never said Toslink was better than anything else.

Suggest you contact Apple if you're interested in the MacBook's optical output.

PS- I'm glad I didn't follow your advise and go with a USB SPDIF converter. The MacBook's optical output sounds great
especially at 24/96.
Kana, Monster sells a bunch of things called iCable for iPod connection. Can you identify the specific model you are using from Macbook to DAC?

I never recommended going with a USB SPDIF converter, not sure one exists actually. But then again, you make things up as you go anyway, so not surprised...SPDIF sucks, much like most of the information you contribute to these threads.

And if you are using WAV with itunes, it just proves your a class A buffoon. I bet your database looks great. Maybe you smash your head on a volcanic rock, but honestly your nothing more than a nuisance. Good luck with your set up.

Couldn't find it on the Monster's site, but here's the one I'm using:

I got mine at the local Mac store.

You could also use a mini plug to Toslink adaptor, and use
any Toslink cable.
Can't we all just get along?

Please grow up and stop the silly name calling and insults.

You posted: "Better off with USB output for sound,"
since I don't need a DAC, that would require a USB to SPDIF converter.

There are lots of these devises on the market.

SPDIF can produce excellent results if it's properly implemented.

Thanks, my Slimserver WAV database does look great. I used WAV on the MacBook so I could compare it to the SB3. If I
get a MAC, I'll use AIFF.

Have a nice day.