First a note on the tube itself: The tube is a very rugged, long-life Russian military Triode specifically designed for oscillation purposes... which is its function here. It is running very conservatively so life expectancy is roughly 5 to 10 years of operating time. The small glass envelope guarantees very low microphonics.
Triode tubes are inherently low noise devices, and extremely linear when used properly. This means that the oscillation frequency wave it produces is very pure and clean. The noise in the sidebands, from 10Hz to 100kHz on either side of the oscillation frequency, is extremely low. This is the important spectrum for audio. Everything below and beyond that can be ignored.
When you reclock the inputs, any noise that is generated here appears unfiltered and unattenuated at the input of the conversion chip, and injects jitter, which from then on is an indistinguishable part of the digital audio stream. No amount of cleaning will ever be able to remove this noise once it reaches this point; it has become part of the audio signal. This noise "rides" on the audio signal, so you do not hear it as noise, but as smearing of notes and masking of detail. There is a distinctive loss of dynamics, tonal purity, inter-transient silence, and sense of timing. We call this "noise modulation."
This is why the low noise, especially in the 10Hz-100kHz sidebands of the oscillator, is so crucial. Again: below and beyond these frequency extremes is trivial, because it will not affect the audio, and will not reach the analog outputs.
When the clock is used to clock the DAC chip, a similar situation occurs as described above: the noise appears at the location where the digital audio stream is converted to successive steps in a staircase wave, which represents the analog audio signal. Each step has to be EXACTLY 1/441000th, 1/96000th, 1/176400th, or 1/192000th. The injected noise introduces a deviation in time which is the exact replica of that noise. This means that the audio signal at the outputs of the DAC chip has the noise riding on it, again as an inherent part of the signal. No amount of filtering will remove the noise once it reaches this step. Again we experience that smear and detail masking, with that distinctive loss of dynamics, tonal purity, inter-transient silence, and sense of timing. Here you see how much sense it makes to reclock BOTH the inputs AND the DAC chip.
The oscillation frequency wave a tube produces is a sine wave. That´s no good: It has to be converted to a square wave. This is a very delicate procedure: when the rising and falling edges of a square wave are not steep enough, there exists a certain window during which the actual transition of the data bit is not exactly time-defined. It leaves room to be either too late or too early. This is a partly random process, and partly dependent on surrounding conditions; such as power supply voltage variations, ground noise, inherent CMOS or chip crosstalk in the decoder or DAC chip, etc. All these timing variations are noise, and are called jitter from various sources. The steeper the edges, the more exactly defined the transition moment will be, resulting in less noise (jitter). When a clock produces a very stable frequency with such low jitter, there will be a more accurate reproduction of the original analog waveform of the music.
Here are a few real SuperTubeClock™ pictures of what it can do: experts will certainly like them. No other commercial clock on earth will produce a square wave as this one.
Each square wave seen below is measured on a Philips PM3295A analog 400MHz oscilloscope using LeCroy 10:1 probes. These probes attenuate the signal by a factor of 10, in order to not load the device under test with any load, resistive or capacitive. So the vertical resolution on the scope image has to be multiplied by 10. For instance when you see ~0.1V, then it is in reality measuring ~1V(AC).