Specifications

2.50
Applications Manual
© 2003-2005 Prism Media Products Ltd
Revision 1.11Prism Sound dScope Series III
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'.
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.
fs
- Abbreviation for sample rate.
FS
-
Full-scale amplitude
.
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
.
IEC60958
- A two-channel digital audio interface standard, as provided at the dScope's Digital
Output and Input. Also known as S/PDIF this format is used in consumer applications usually with
an unbalanced phono/RCA copper or TOSLINK optical connection. It carries audio wordlengths up
to 24 bits, plus Valid bit, User bit,
Channel Status
and Parity bit per channel.
IMD
- Intermodulation Distortion. When a signal consists of more than one frequency, a non-linear
device under test will produce the original frequencies plus an infinite number of IMD products,
given by
(a * F1) + (b * F2) + (c * F3) + ...
where (a, b, c) etc. are all possible integer numbers, and (F1, F2, F3) etc. are the frequencies of
the original tones.
Jitter
- Variation in edge-timing of a clock. In audio systems, manifestations are interface jitter and
sampling jitter.
S/PDIF
-
IEC60958
.
UI
- (Unit Interval). A UI of an AES3 or
IEC60958
carrier is 1/128 of the frame period, the duration
of a single biphase-mark 'cell', or half a bit period.