USB Length, jitter and Volume Control Questions

I've been working on a PC audio system for a few months now and I have a few questions that I cannot find the answers to.

I have a new iMac running USB>DacMagic DAC>Onix Sp3>Merlin TSM speakers. I hav had a Valab NOS DAC for a bit and have a Stello DA100 on the way. My questions is how does the volume work in these setups? With the DacMagic I can control the volume through itunes but not through the system menu bar. With the Valab I could control both iTunes and system volume. Is there a difference between the two? Does using the volume control in iTunes or system conpromise the sound? If I'm getting gain from the computer (regardless of system volume or iTuens volume) am I not essentially using the computer as a lowgrade "preamp".

Also, how long can a rung of USB cable be before the signal begins to degrade? Does USB transfer introduce jitter?

If memory serves me correctly, Steve from Empirical Audio said you don't want to exceed 15 feet of USB cable.
That's essentially what it says in my new Music Streamer+- 5 meter max. Interestingly, it also says the shorter the better. Great little (and I do mean little) DAC! Highly recommended.
Did you ever try Firewire???
I have not tried FireWire. I have a drobo hookedup to my only FireWire port. Can you daisy chain audio with storage?

I'm also thinking about getting either an airport express to toslink or a 30 ft toslink cable and bypassing USB altogether.

If you want the best results for jitter, I would go with a 1.5m cable for USB. Same with S/PDIF cable for the following reasons:
Unfortunatly I don't have the ability to use a short cable unless I go wireless (airport express to toslink). My library is 30 feet away.
I tried running wireless via I-Mac to Airport Express to Empirical Audio Pacecar to my DAC. Was not happy with the results and have since gotten out of computer audio.

Next time I try computer audio, I'll buy a Mac Mini direct to a DAC (MHDT Paradisea or comparable) via USB. I don't think you'll be happy with a long (>15 ft) cable or wireless to an airport express) unless sound quality is not important. Suggest you invest in a Mac Mini, a good, short USB cable and a USB capable DAC.
The problem with AirPort Express and AppleTV is that they both muck-up the data doing the conversions to ALAC and back as well as the mucking that Core Audio does.

I understand that much of this can be circumvented now using Amarra and a tool called "Airfoil". If you use Airfoil and select the internal speakers, the Amarra feed evidently goes directly to AirPort Express or Apple TV.

Steve N.
If the files you are pushing across the airport are already in mp4 (ALAC) does it still go through the conversion?

Also, would using Airfoil and selecting "internal speaker" use the internal DAC in the Mac?
I use a 3 meter USB cable with my Ayre QB-9 and the results are great.

As for volume control, you absolutely want your volume control at 100 or 0db. Otherwise, the computer is doing math that compromises the sound.
Steve N: Could you elaborate on the issues with Apple TV or direct me to another discussion or send a private email? I currently use Apple TV with a PS Audio DAC and have been pretty happy, but I would like to extract the best sound I can. My library (1600CD's) is ripped in ALAC.

Bbopman: Two issues with AirPort Express and ATV:

1) ALAC is the only format transmitted
2) iTunes is the player

The sonic issues with ALAC cannot be avoided unless you use Transporter, Sonos, Squeezebox or Duet etc..

The sonic issues with iTunes can be avoided by using Amarra or Amarra Mini. See

If you have a truly resolving system, then you will hear the difference in these. If not, then you probably wont care.

Steve N.
Empirical Audio
I have been happy with iTunes Airport Express and ALAC. You need to know how to get all the settings correctly in order to preserve bit transparency (volume at max, no EQ etc.) Most people on Head-fi seem to agree that iTunes ALAC can be bit transparent when used carefully with the right settings.

I did direct comparisons between a CDP and Itunes both output optical to the Benchmark DAC1 - perhaps my tin ears or my unresolving system or perhaps there actually is no perceptible difference. (My interest is CD redbook lossless quality only - I have not experimented with higher resolution formats and I have also not tried to compress using AAC or MP3, which surely will degrade the sound)

That said, PC or MAC audio is a bit of a minefield - a pesky software bug which could perhaps creep into the next release of iTunes might make me feel different about this issue.
I have the same setup as Shadorne and also cannot hear the difference between Aiport Express and CDP (same Benchmark DAC1).

"Front Row" on Leopard doesn't work with Airport Express and that's what Airfoil is for. It can transfer Front Row/Itunes or any system sound to Airport Express (in the background).