Manual

1.23

Operation Manual

Revision 1.01Prism Sound Callia

Listening experience

In practice, it seems that the benefits of careful clock design are very apparent in listening tests. On

the other hand, it can sometimes be difficult to expose the shortcomings of converters with poor

clocks, because these units often have other analogue problems whose severity might obscure

jitter-related effects.

In general, some of the widely-noted effects of sampling jitter are not surprising – for example the

muddying of brass, strings and high-frequency percussion and the loss of stereo (or multi-channel)

imaging. These are well explained by the worse distortions which result in the lab at loud, high

frequencies, and the way that sampling jitter produces quiet, aharmonic components, perhaps only

subliminally perceptible, which blur our impression of the ambience which creates a soundstage.

Other effects are harder to explain – for example there is wide observation that large amounts of

sampling jitter can take the edge off extreme bass rendition. Such reports are probably too

widespread to be ignored, but defy explanation within current theory.

Callia and CleverClox

Callia is designed to source clocks which are as stable and accurate as possible, and also with the

aim of being insensitive to the quality of incoming S/PDIF clocks. It is designed to remove jitter from

any selected reference sync source before it is used as a conversion timebase, so as to eliminate any

audible effects of sampling jitter, whatever sync source is used.

Callia does this with the help of Prism Sound's unique CleverClox clock technology, which removes

the jitter from any selected clock source down to sub-sonic frequencies, without the need for a

narrow-band quartz VCO. CleverClox can adapt to any reference, irrespective of frequency, and

regardless of how much jitter it has, derives an ultra-stable conversion timebase.

6.3 Analogue interconnections

To maintain the high sound quality of Callia, it is important to follow some basic guidelines when

making analogue connections to the unit. This section discusses some things to watch out for.

Cable quality

Use of good-quality, heavy duty audio cables is recommended. Cables with heavy screens are

recommended, especially for unbalanced use. Owing to mechanical differences between connectors

from different manufacturers, it is advised to use cables with identifiable connectors from reputable

manufacturers. This is especially true for headphone jacks, where unreliable tip connection can

occur owing to the slightly non-conforming shape of some manufacturers' parts.

Balanced versus unbalanced connections

Where possible, balanced interconnections should be used, since the audio signal is represented as

a voltage difference between two dedicated conductors (neither of which is ground-coupled), which

are usually closely-twisted to ensure that any interference pickup is cancelled out. In unbalanced

connections, the signal is represented as a voltage difference between a single signal conductor and

an accompanying ground conductor. Where dynamic ground-potential differences exist between the

source equipment and the receiving equipment, this difference is effectively added to the unbalanced

audio signal.

This effect has long been familiar in audio systems as 'hum loops', where the variation in ground

potential occurred at line-frequency, and was developed by the flow of line-frequency currents to

linear power supplies. Hum loops were usually resolved by either steering the currents along

non-critical routes by re-arranging the topology of the system ground interconnections, or by