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Monarchy DIP/Scott Nixon Dac vs. USB Scott Nixon Dac? - Page 2

post #16 of 18
9/3/06 at 1:05am
I have not looked at the Hagerman in detail but I believe thay are just another USB audio single chip solution.

I am not endorsing anything since the product does not exist yet but Steve (audioengr) has announced in a different thread that he is working on a USB solution with a secondary reclocking circuit. However, from what he ha disclosed this will come at a price.

I am still hoping that one of the USB chip prociders will provide an integrated solution for USB2 with async support.

Today, I believe both the TAS3020 and the USB chips from Bridgeco can be programmed with additional firmware to support that mode. Windows supports async out of the box.

Cheers

Thomas
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post #17 of 18
9/3/06 at 2:01pm
Quote:
Originally Posted by thomaspf
For the Highest quality conversion you will not want your DAC to follow either a I2S clock signal or a S/PDIF input. You will want a crystal oscillator driving the converter chips directly and then pace the source to match your speed. This is what asynchronous USB audio and master clock DACS are all about.

Thomas - the DAC chip interfaces directly with I2S. This does drive the converter chips directly on most DAC chips....

Also, concerning asynch mode for USB: I believe as you do that the flow control is much improved over synchronous, however I also believe I read that Isochronous transfers are not possible with asynch. It is really not designed for real-time streaming.

Steve N.
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post #18 of 18
9/3/06 at 2:36pm
The async mode allows the clock to reside in the audio device.

The audio data still travels over an isochronous endpoint to the device but there is an additional isochronous stream from the device to the PC to do the flow control. In this case the PC is slaved to the hardware clock in the USB device. (e.g. Audigy 2NX)
You can easily observe this with a USB monitor.

In isochronous mode there is a software clock in the PC that tries to send out data in a somewhat steady rate and the chip in the USB device needs to estimate the average rate and try to smooth out the variances via a buffer and a software PLL. The I2S signals on these chips are generated from this process.

http://www.usb.org/developers/devclass_docs/audio10.pdf

Cheers

Thomas
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