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In Reply to: RE: Hardware Attack!... Re: Is it worth it....? posted by Frank Mena on November 06, 2009 at 06:16:53
Having played with lots of USB-to-spdif gears, even some pretty tricked-out ones, I feel this is the bottleneck in most systems that use these devices, even the one pictured.
I'm sure the modded box greatly improves sound, but ultimately one would want to use a non-USB solution, unless one can come up with completely asynchronous USB interface, powered correctly...
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I ain't so sure about the details, but the Musiland gizmo thingeymaboby seems to work asynchronous, it certainly does not work as traditional USB device (transfers data in bulk mode using it's own driver, did not waste much time with this thing).
It uses on board pll to make the audio clocks from a single crystal (not a bad thing itself - the "nah-nah-pll" sayers not withstanding, the TC firewire solution used by Weiss does the same and well).
What dat sez iz - a dirty power supply will make trouble. The crystal circuit also runs of the same dirty chip power taken from USB, I'd say we have double trouble, when we want no moh troubles.
We have a jittered clock we use as referee for a fractional division pll with vco badly modulated from supply.
Who just said "Desaster Area"? Was that you Zaphod?
My Musiland sounded much worse than me modified spdif motherboard. Dub no ear good. So me send it back.
No idea how good these supplies and clocks are, but what the guys at diyhifisupply are doing should help the problems well, so no reason dub not ear good!?.
Seems an awful bodge though, not very artful at all.
Greez TAB
I found John Swenson's post on the Musiland.
http://db.audioasylum.com/cgi/m.mpl?forum=pcaudio&n=59851&highlight=musiland+john+swenson&r=
So much for that, as it seems Musiland's asynchronous is not the proper asynchronous USB implementation at all..
Not sure why is that.asynchronous:
"In a synchronous system, operations are coordinated under the centralized control of a fixed-rate clock signal or several clocks. An asynchronous digital system, in contrast, has no global clock: instead, it operates under distributed control, with concurrent hardware components communicating and synchronizing on channels."
So either it is or it isn't. The Musiland uses an onboard local clock and its own driver instead of an MS driver. I'm not sure that is an issue relating to sound quality.
The key here is how good the audio clock is. Being asynchronous means its output jitter depends on how good the Musiland audio clock is.
In the Musiland a simple 24MHz clock generator is used that runs off the main powersupply, which is fed directly from the PC's USB power line. This will create a very jittery reference clock for starters.
This clock forms the reference of a "fractional division PLL". Such a PLL is used to make non integer multiple clocks from a reference clock. It can never be any better than the reference clock. The DIYHFS EZ Clock with a 0.5ppm clock generator provides as close as possible to the ultimate as reference clock, eliminating this issue.
There are many varying PLL implementations, however a crucial thing here is that the PLL will contain another clock generator which is MUCH more subject to jitter from power supply noise. So by feeding this PLL a clean supply, jitter is minimized.
Purely from a viewpoint of potential jitter (which we cannot verify as having been achieved or not) the Musland system (the chips used) seems to be capable of sub 100pS jitter results, something the Musiland guys also claimed (but their actual design does not achieve it).
All that said, the common Cirrus Logic (Crystal) Receivers and most others add over 100pS jitter of their own, so I should think the SPDIF Receiver would be the limit in the DAC.
If receivers used have low jitter of their own and equally good suppression of external jitter, all of this is moot anyway.
The Musiland is cheap and the mods done do not cost the earth either (there are more expensive USB2SPDIF boxes out there that do less). So I think one can easily defend the Musiland USB to SPDIF converter with modifications as a good way and economical way to make a computer transport for a pre-existing SPDIF DAC capable of 24/192KHz. That's all.
regards
Brian
DIY - Done Right!
Edits: 11/10/09 11/10/09
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