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The difference of Synchronous and Asynchronous DACs (slightly technical)

post #1 of 5
Thread Starter 

Hi Guys,

I am a computer engineering student in university and I recently learned about the difference between Synchronous and Asynchronous digital circuits in my studies.

I had been wondering about these for a while and I thought maybe it is good to share the knowledge.


basically a synchronous digital circuit runs on a clock, the clock is a signal that changes value periodically, (for example a 50 MHz clock changes values 50 million times a second).

I wont go to gruesone detail but a synchronous digital circuit is designed in a way that it finishes one instruction on every clock cycle, thus doing instruction in discrete time.


on the other hand, an asynchronous digital circuit, is one that does not have any clock at all, and it continously gives out outputs (depending on the inputs and previous states of the input).


a synchronous circuit is usually easier to implement and understand but it is not always the fastest and the most efficient (since the clock signal needs to be distributed to every component, the chips heat up more, more power is needed, etc...)


synchronous circuits are usually more stable than their async counterparts (for obvious reasons)


I hope that helps.


P.S, these digital circuits are sequential circuits (vs, combinational circuits) but wont go to gruesome detail, if you are interested look up sequential logic. a DAC is a digital circuit for the most part.

post #2 of 5

There's probably a few threads on that, besides this one.

post #3 of 5
Thread Starter 
Originally Posted by Mad Max View Post

There's probably a few threads on that, besides this one.

true, but they are far too technical and I do not consider them to be illuminating for the non-technical enthusiast. that is why I wrote this.


post #4 of 5

Well, I think it's like DAC chips....that don't mean much out of their surrounding circuit. I've got no problem believing that a well designed PCM1793 DAC will sound better than a poorly designed PCM1794. The former only requires 2 opamps as LPF, the latter 4 as LPF and another 2 as buffer...easier to goof up somewhere, and go cheap to save costs.


A well designed isochronous transport(using the WM8804 reclocker to straighten things up for instance) might/would/will sound better than a poorly designed async solution IMHO. And who knows what happens in the back? Musiland first advertized their "Monitor" serie as isochronous, then all of a sudden called it async. Many ppl feel that the Cypress USB chip they're using isn't real async...the same has been said about the Hiface, a major manufacturer called it a very poor async implementation.


the High Face device.  I have been looking at the chipset they use and it’s clear that while technically asynchronous it is done in the wrong way and I wouldn’t be happy with the results.  By that I mean the chip they use claims to be asynchronous but they use the internal clocks and it goes through some unacceptable processes that is severe enough to have prevented us from licensing what they are doing.


God knows what is true and what isn't...just like w/ DAC chips, there's only way to find out whether you'll like it.


TC Electronic have a few papers about jitter in their digital library, they like it fully async but they don't diss the reclocking approach...they simply call it cost ineffective and harder to implement properly.

Edited by leeperry - 3/3/11 at 12:42pm
post #5 of 5
Is the HifimeDIY Synchronous enough for Spotify Premium (320kbs) or should I go for the asynchronous?
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