Listening Experience; Synchronization And The Ada-8; Extended Sample Rates And Split96 Interfacing; What Are 'Extended' Sample Rates - Prism Sound ADA-8 Operation Manual

Prism Sound ADA-8 Multi-channel A/D D/A Converter Operation Manual - Revision 1.00
the frequency of the jitter itself. These components get louder as the amount of jitter
increases, but also as the frequency of the converted tone increases. So sampling jitter
produces distortions which should sound much worse than conventional analogue harmonic
distortions, since the spurious components appear at aharmonic frequencies. High audio
frequencies should suffer worse distortion than low frequencies. For low-frequency jitter, the
resulting distortion sidebands appear close in frequency to the audio signals which produce
them – this should mean that they are 'masked' from our hearing by the same phycho-
acoustic phenomenon upon which are based sub-band (perceptual) coding schemes such as
MPEG. This is fortunate, since it is quite difficult for a PLL to remove jitter to a good degree
even at moderate frequencies, but for very low frequencies it would be very difficult indeed.

7.1.4 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 marr 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.

7.1.5 Synchronization and the ADA-8

The ADA-8 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 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.
The ADA-8 actually contains two independent clock generation and conditioning circuits,
allowing generation of, or synching to, two independent sample rates at once. Normally one
is used for each of the ADA-8's two Paths.
An unusual feature of the ADA-8 is that a Path can be locked to reference sync sources at
different rates from the Path's desired sample rate. In this case, the ADA-8 maintains a
constant ratio between the reference sync and the Path's sample rate. For example, if the
selected incoming reference sync is identified as being close to 44.1kHz, and the Path is
explicitly set to sample at 48kHz, the Path's sample rate will follow the reference rate
multiplied by 48000/44100.

7.2 Extended sample rates and Split96 interfacing

7.2.1 What are 'extended' sample rates?

Sample rates above 48kHz are often referred to as 'extended' sample rates. Selecting an
extended sample rate for an A/D Path allows the inclusion of higher audio frequencies in the
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