Digital Drive Upsamplers, DACs, jitter, shakes and analogue withdrawals, this is it.

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just my 2 pennies

Posted by Gordon Rankin (M) on January 21, 2011 at 08:59:06

In Reply to: USB DACs and Inputs...I don't really get it. posted by Regor Ladan on January 20, 2011 at 12:30:25:

Regor,

SPDIF has never really been a good medium for transmitting audio data. Sure we have had years to get close to perfection, but really we have exhausted the band aids we can put on the interface to really get good sound.

The ultimate problem is that SPDIF cannot never be truly asynchronous with the master clock to the DAC chip. I don't mean async upsampler... I mean the actual clock that runs the DAC chip. SPDIF has a moving clock and therefore that creates jitter and you can reclock, reclock with FIFO, upsample whatever and all that will help... BUT again just a band aid.

So with USB we are given a recognized protocol with real specifications and the use of a protocol called Asynchronous USB that allows the flow of data to the DAC chip to be controlled on the DAC end and not on the computer end (or transport end). This allows us to design a DAC with fixed clocks which obviously will have significantly less jitter from the get go and therefore result in better and more consistent sound.

PART 2!

Ok so the interface is better with USB... and those of you asking about Firewire well... That can be Async but most of it is not and that will add jitter and these have secondary PLL/DLL and other stuff. Only MetricHalo I think has an async Firewire interface.

Ok so are all USB interfaces the same? NO!!!!! There are many that are adaptive and these would require secondary PLL, reclockers etc... just like SPDIF to work well. Again a band aid approach to good sound.

Ok are all USB Asynchronous interfaces the same? NO!!!!! some rely on the USB controller to create the Master Clock from a PLL. This is a very bad thing. Other companies who are more software companies and less audio, don't really understand what it takes to make a really stable Low Jitter Oscillator for use as a Master Clock. These will also suffer with poor performance.

Now WIFI is not a good medium for transferring data. It just not have the bandwidth to really do anything other than red book. Also the contamination of RFI into the DAC is very high. Ethernet is also not a great medium as the packet size and speed are significantly lower than USB (100Mhz vs 480MHz).

PART 3!

High Res has never found a good footing anywhere in audio. The masses really don't care and we are merely 0.1% of all the consumers of this medium. Well most of the red book music we play is based on some master files usually at 24/88.2 or 24/176.4. They use these because it sounds better to get the Master Files down to red book 16/44.1 because 44.1 is a multiple of 88.2 and 176.4. Not many Mastering engineers use 24/96 or 24/192 as these are not multiples of 44.1.

Anyways... The Master Engineers and Record companies now realize that with little work or outlay of cash on their end that they can distribute Master Files and make money. Heck the works done, there is no physical medium to muck with and therefore it's a no brainer.

Computer Audio therefore allows the user to do standard red book better than a transport: error free and boats loads of memory really help out. Also the computer reads the disk, not as a stream but as data, just like an application. Computer Audio allows, downloads now for High Res and so much more.

But the biggest thing that I get emails daily about is that, customers tell me they listen to more music and stuff they have never heard before and the control and output is significantly better than any transport they have owned.

Plus a really good transport cost tons over what a Mac Mini decked out with an SSD drive and 8G of memory.

Thanks
Gordon
J. Gordon Rankin

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