Specifications
2.15
Applications Manual
© 2003-2005 Prism Media Products Ltd
Revision 1.11Prism Sound dScope Series III
3.2.3.8.3 Digital-to-digital jitter susceptibility
Applies to:
EUTs with digital audio inputs and outputs.
Aim:
To measure the
jitter susceptibility
of the
EUT
when presented with jitter of varying frequency at
its digital or reference input.
Method
The digital input of the EUT is driven with a –3dBFS sinusoidal stimulus at fs/4 (where fs is the sample
rate of the EUT). The digital input carrier is phase-modulated with a sinusoidal jitter signal.
The frequency of the jitter signal is varied from 80 Hz to 20kHz in octave steps. The jitter amplitude is
set at the high frequency jitter tolerance limit of the interface, which is nominally set at 1/(512 x frame
rate). The THD+N of the EUT output is measured at each step and then the results are graphed for
both channels.
The measurement may be repeated for other input signal frequencies. Two useful frequencies might
be fs/192 and 997Hz. The operator is asked whether or not to repeat the test for these frequencies.
If the equipment under test has a Reference Sync input other than the digital audio input, then the test
should be repeated with this input driven from the dScope's digital output as well.
3.2.4 Output characteristics
The Output characteristics tests are arranged in the following subsections, which correspond to the
equivalent subsections of the AES17 standard:
Out-of-band spurious components
Suppression of imaging components
Output amplitude at full-scale
Maximum output amplitude
Output-level stability
Digital audio output format
3.2.4.1 Out-of-band spurious components
Applies to:
EUTs with analogue outputs.
Aim:
To measure the total of HF components beyond the audio band which are output from the
EUT
's D/A converter, with no signal applied.
Method
The analogue output of the EUT is measured with no test-signal stimulus. The total RMS amplitude of
all the components above the
upper band-edge frequency
of the EUT is measured for both channels,
and expressed in
dBFS
. Components within the audio band are excluded by using the
standard high-
pass filter
.
The spectrum of the spurious components for both channels can be viewed graphically on Page 2 if
required.