chroot said:
As Evo said, jitter is inconsistency in the time between each sample of a digital signal. If you look at a signal on an FFT, the effect of jitter is to smear out peaks in the spectrum, reducing their peak power and spreading it over a range of nearby frequencies. This causes frequencies that should be distinct (say, the overtone series for a number of different instruments in a symphony) to overlap, ruining the more subtle features of the instruments' timbre.
Hmmmmm, exactly the improvement I observe. Every instrument is made more distinct, every note more clear. Most of the recordings I am comparing I've listened to for years, so I can easily tell the difference. Plus, I've been upgrading all aspects of my system, one component at a time, with the Monarchy DIP the last after adding everything from new cables and DAC to power amps and speakers.
chroot said:
(I'll also note that the entire concept of a "jitter reducer" is hogwash. Once an analog signal has been digitized with a jittery clock, information has been lost. You cannot reconstruct a "jitter-free" digital signal from one which has been poorly digitized. It doesn't really matter how many stars the product got from obscure audiophile magazines; it's not physically possible.)
- Warren
Of course. I shouldn't have said jitter "correction," which Monarchy doesn't claim, but rather they claim jitter "supression." However, Stereophile is hardly an obscure audio magazine! It is the recognized standard for audiophiles; and Stereophile is not the only magazine that praised it. I have yet, in fact, to find a single critique by an audiophile (and there are dozens of them to be found if you Google) that wasn't positive overall both in listening experience and measurements (when taken).
Perhaps I should have asked why the Monarchy DIP works, when so many attempts to improve the jitter situation have failed. One case in point was the high-end audio company Theta (who's DAC I use), who produced a so-called jitter reduction unit which tests showed actually
increased jitter.
In the excellent article Evo referenced (how did I overlook that one?), the author (Dr. Rémy Fourré) suggests how reclocking devices like the Monarchy DIP might help:
"A more significant appraisal of input-receiver performance, however, is how well it rejects jitter in the incoming signal. Does the input receiver pass jitter from the transport to the recovered clock, or does it attenuate it? With well-designed transports and impedance-matched transmission lines, the intrinsic jitter dominates. But with poorly designed transports and impedance-mismatched transmission lines, the incoming jitter not rejected by the PLL becomes the dominant factor. The jitter in the recovered clock (what we're really concerned about) is thus a function of the transport's jitter, the interface-induced jitter, the input receiver's ability to reject incoming jitter, and the input receiver's intrinsic jitter.
By their nature, PLLs reject incoming jitter only above a certain frequency, called the jitter attenuation cutoff frequency. Consequently, we must consider both the receiver's intrinsic jitter and its jitter attenuation cutoff frequency when specifying an input receiver's performance. The single intrinsic jitter specification doesn't tell the whole story.
Barring design and layout errors, the jitter performance of a digital processor is primarily dependent on the input receiver stage. The best currently available monolithic (chip) input receiver is the Crystal CS8412. This has an intrinsic jitter of 200ps and a jitter attenuation cutoff frequency of 25kHz. With no input signal, the CS8412 will introduce 200ps of clock jitter. Jitter in the incoming data stream with a frequency below 25kHz will be passed to the recovered clock. The performance achieved by the best currently available hybrid digital audio receiver (UltraAnalog AES 20) is typically 40ps for intrinsic jitter and 1kHz for jitter attenuation cutoff frequency.
These criteria for specifying input receiver performance also apply to "reclocking" devices that claim to reduce jitter in the data signal. These devices receive an AES/EBU or S/PDIF input signal, recover the clock from this signal, and reclock the output signal with this improved clock. Just as with an input receiver, we want to know the device's intrinsic jitter and its jitter attenuation cutoff frequency. A reclocker can only be as good as the input receiver it uses.
Reclockers have two major limitations. First, if the CD transport's intrinsic jitter is less than the reclocker's intrinsic jitter (in the DC-40kHz band), the reclocker can only add jitter. A reclocker can improve high-jitter transports, but it degrades low-jitter transports (footnote 8). Although the output clock may appear much cleaner on an oscilloscope when high-frequency jitter is attenuated, it doesn't mean there is less jitter in the DC-40kHz band. Remember, only jitter in this band can affect a multi-bit converter's sonic performance. Only a spectral analysis of the jitter can reveal whether these devices improve or degrade the signal.
The second limitation of reclocking devices is the reclocker's jitter attenuation cutoff frequency. If it isn't lower than that of the digital processor's input receiver, the reclocker will simply pass incoming jitter at frequencies which will be rejected anyway by the digital processor's input receiver."
In any case, thanks to you and Evo for clarifying the issue.
