Why USB to SPDIF and not optical?

"XP generally upscales 44.1 files to 48 unless special drives are installed."

Not true. My USB converter uses the native drivers and it outputs 44.1 on XP. There are several ways to avoid kmixer, including:

1) unmapping the device
2) Kernel Streaming
3) ASIO

Steve N.
Empirical Audio

Just improving the Toslink from the Mac will reduce jitter a little, but it does not change the clock inside the MAc, which is the true source of the jitter.

If you go USB to S/PDIF, there are three advantages:

1) Eliminate the Toslink optical conversions as a source of jitter
2) Establish a new low-jitter clock to replace the one in the Mac
3) Output from S/PDIF coax to the DAC, whic has the opportunity to have lower jitter than the Toslink (depending on implementation)

BTW, this can still give you galvanic isolation (just like the optical) providing the converter is properly transfomer coupled.

Steve N.
Empirical Audio

"If there is no additional software other than the native drivers, I would suspect that the upconversion still happens. Do you concur? Does your converter get 44.1 out of iTunes?"

No, not with Vista and my converter. It changes 16/44.1 into 24/44.1, so Vista is bit-perfect.

With XP, there is something changed if you dont use Kernel Streaming, but it is not necessarily 44.1 to 48. I believe there is volume adjustment DSP, just like Vista does with 16-bit data.

I dont recommend using iTunes on any PC with any device, even WiFi. Use Mac with iTunes.

Have you tried Jriver?

Steve N.
Empirical Audio

"Do you get 16/44.1 out of J River?"

Yes, but with my USB converter it's 24/44.1. With some devices attached to my Pace-Car, it's 16/44.1. The Sonos is also 24/44.1, but bit-perfect.

"If I read your comment correctly Vista converts 16/44.1 to 24/44.1, so I would not call that bit-perfect."

Vista and XP both change 16/44.1 into 24/44.1 with my USB converters. It's bit-perfect. The data is not modified. The noise floor is just lowered.

"Is your software adding the bits or is Vista?"

Both, its the firmware of the USB interface talking to Windows audio stack S/W in XP and Vista.

I think your problem is iTunes. If you use Jriver or Foobar and either unmap or use Kernel Streaming with XP, you will be bit-perfect. The sound quality will be a lot better too. I recommend Foobar 0.8.3.

Steve N.
Empirical Audio

"Hey Steve.

Why is Kernel Streaming better than ASIO for KMixer avoidance?"

Because at least with XP, every ASIO plug-in that I have tried sounds different. I dont trust them anymore. Unmapping has a clarity that ASIO just does not delivery IME.

Steve N.

Dtc - it turns-out that hardware upsamplers are mostly inferior to software upsamplers. Makes perfect sense. There are limitations to what you can do in hardware and how long it takes to do it. It usually a compromise.

Software on the other hand is more flexible for editing and integrating the latest algorithms, and for file re-writes (such as R8Brain and Adobe Audition), the S/W can take all night to do the upsampling task, and it often does. More time to do it equals better quality. Not all upsampling algorithms are equal either.

Steve N.
Empirical Audio