[ampgalore]

To all headfi resident electronics gurus, where does jitter come from?

If I rip all my CDs to wav files to a harddrive, then hook up the optical out on my soundcard to a receiver's DAC, will there still be jitter?

 

[Wodgy]

Source jitter is caused by the source's clock. You don't get rid of it by playing back music files from your hard drive. It all depends on your sound card. Stereophile publishes jitter measurements of the sound cards they review, on the few occasions when they measure sound cards. The RME 96/8 PAD, for instance, has a moderate amount of jitter. Not as much as a good transport, but less than a cheap transport.

 

[Budley007]

Just a quick question...Doesn't a DAC that use it's own word clock reject a certain amount of jitter from the incoming signal?

 

[jefemeister]

jitter will occur whenever a clock signal is sent over a distance (this is actually only one of many jitter sources.) Using a harddrive does not chage the fact that the digital signal must be sent to the DAC over a wire. Devices that use word clock inputs will buffer the data inbetween transport (or drive) and DAC. The wclk reference is PLL'd up to the bit clock frequency (typically 16.9 MHz for redbook). This clock is used to clock data out of the buffer and the original bit clock (embedded in the AES data) is used to clock data into the transport. So effectively you've elimianated all of the jitter introduced prior to the DAC circuit. The wclk reference is used only so that the frequencies on both sides of the buffer are the same so that it will not over or under run.

 

[clarke68]

Quote:

Originally Posted by ampgalore where does jitter come from?

I don't thoroughly understand jitter (few do), but as jefemeister said, there are several different types of jitter that come from a variety of different places.

From what I understand, the most audibly damaging type of jitter is "interface jitter", which is inherent in the s/pdif interface...something to do with interference caused by sending the clock signal and the audio signal over the same line. Any time you send the signal over a toslink or coaxial cable, you get jitter.

This is why outboard jitter-reduction devices are a somewhat flawed concept. Most use a dual-pll scheme to reduce jitter, generate a bunch of emi, and add more jitter as the signal is again transmitted via s/pdif to the DAC. Not saying that jitter-reducers won't improve your sound, its just they don't necessarily do so by reducing jitter.


Quote:

Originally Posted by Budley007 Just a quick question...Doesn't a DAC that use it's own word clock reject a certain amount of jitter from the incoming signal?

The best way to eliminate the effects of jitter is to use a jitter-immune DAC (like the Benchmark). There's a few different ways to deal with jitter inside a DAC, (generating its own clock may well be one of them) but I don't understand any of them very well.


Quote:

Originally Posted by ampgalore If I rip all my CDs to wav files to a harddrive, then hook up the optical out on my soundcard to a receiver's DAC, will there still be jitter?

Way. Evidently the clock signal is highly susceptible to outside interference, which is plentiful in a PC (from dirty power and other clocks on the motherboard).

That said, I'm a "computer source > s/pdif out > outboard DAC" guy. I'm sure the setup I'm using has jitter, but never having heard anything else, I don't know how serious a problem it really is.

According to Bob Katz, some of the audible effects of various types of jitter include "an intermodulation, a high-frequency edge added to the music", "spurious tones to appear at low levels, blocking our ability to hear critical ambient decay and thus truncating the dynamic range", "a small perfume of hiss at the lowest levels", and "a 'veil' on the sound".

Ever noticed any of these in your system? No? Maybe you don't need to worry about it...

 

[Hello]

I'm not an electronic's guru, but I'll take a stab at answering your question. Yes, you'll still have jitter. From my understanding, every setup has some jitter -- the question is how much. The nice thing about DAC's that are "jitter proof" (like the Benchmark) is that they eliminate virtually all the jitter from the inputted digital stream. However, even these DACs still have jitter because some is introduced during the processing or conversion of the signal.