Specifications

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2.80

Applications Manual

Revision 1.11Prism Sound dScope Series III

5.3 Glossary

The following definitions are used in the Dolby Digital test procedure and in the dScope

implementation of the Dolby Digital tests:

Channel Status

- status information embedded in an AES3 or

S/PDIF

digital interface, one bit per

channel per sample-period, which accumulate into a 192-bit frame for each channel every 192

sample-periods. The frame is arbitrarily split into many fields of various lengths, with diverse

functions as described in the appropriate interface standard document. The definitions of the fields

and their meanings are different for 'Consumer' Channel Status (where the first bit of the frame is

0, used in S/PDIF) and 'Professional' Channel Status (where the first bit is 1, used in AES3).

D/A line-up

- A setting of the dScope's Inputs and Outputs which relates the maximum analogue

amplitude to the maximum digital amplitude. It is expressed as an analogue amplitude which

corresponds to 0dBFS (full-scale digital). This feature of the dScope is especially useful in

measuring

EUT

s with both analogue and digital ports since it allows settings or measurements in

one domain to be expressed in the units of the other. For example, an A/D converter can be

stimulated with a signal 1dB below that which will produce full-scale output by setting the dScope's

analogue generator amplitude to –1dBFS, provided that the dScope has been set to the

appropriate D/A line-up for the converter.

Data jitter

- A type of interface jitter. Data jitter is that part of the interface jitter which is caused by

variations in the duty cycle of the AES3 or

IEC60958

carrier acting with high-frequency losses in

the transmission medium (e.g. cable capacitance) such that edge timing in the carrier is modulated

by the activity of the data bits. This is distinct from fs jitter, which is inherent in the carrier source.

dScope can measure data jitter and fs jitter independently, so that the cause of jitter problems can

be identified. Also referred to as 'inter-symbol interference'.

dS-NET

- A proprietary serial interface used to connect peripherals such as I/O Switchers to the

dScope.

dBFS

- A logarithmic unit used to express signal amplitude in digital and mixed-domain systems in

terms of the maximum amplitude which can be accommodated by an

EUT

. A 0dBFS signal has

the same RMS amplitude as a sine whose peaks just touch the maximum level of the system. A

–6dBFS signal has half this amplitude, for example. Note that for non-sine signals such as square

waves or DC it is possible for the system to accommodate amplitudes greater than 0dBFS. In the

dScope it is possible to specify or measure analogue signal amplitudes in dBFS, in which case the

D/A line-up

is used as a reference.

EUT

- 'Equipment under test'.

Eye-diagram

- The AES3 and IEC60958 standards define acceptable carrier degradation in terms

of amplitude and edge-timing using an eye-diagram, which shows the minimum acceptable

differential carrier amplitude over a defined period within 1 UI of the carrier. This can be verified on

the dScope using the Carrier Display feature.

Eye-narrowing

- The dScope can measure the worst-case narrowing of the eye of an AES3 or

IEC60958 carrier. This is essentially a measurement of data jitter, and can be referred to the

eye-

diagram

in the AES3 or IEC60958 standards.

Folding frequency

- Half the sample rate of the

EUT

. Input frequencies above the folding

frequency are subject to aliasing. Where an EUT applies internal down-sampling, the folding

frequency is half of the lowest internal sample rate employed.

- Abbreviation for sample rate.

Full-scale amplitude

- A signal whose amplitude is the maximum which can be accommodated

by the

EUT

. In the case of a sine, this amplitude is 0

dBFS