Specifications

2.11
Applications Manual
© 2003-2005 Prism Media Products Ltd
Revision 1.11Prism Sound dScope Series III
3.2.3.1 Suppression of alias components
Applies to:
EUTs with analogue inputs.
Aim:
To measure the
alias components
in the
EUT
when presented with out-of-band HF
components at its analogue input.
Method
The suppression of alias components is measured using a sinusoidal stimulus with amplitude
–20
dBFS
. The frequency of the signal is first set to 997Hz in order to establish an output reference
level. Once the reference level has been established and set in the dScope, the signal is swept from
four times the sampling frequency or 192kHz (whichever is lower) to the
folding frequency
.
It is currently not possible to make this measurement as stated in the AES17
standard using the dScope, since the specified sweep range could extend to
192kHz. Using a dScope with 192kHz analogue sample rate it is only possible to
generate frequencies up to about 90kHz. However, this frequency range is adequate
to reveal aliasing under most conditions.
For measurements made at the analogue output of the EUT, the signal is filtered with the
standard low-pass filter
, which may be cascaded with a notch filter at the frequency of the applied
stimulus, if necessary, to suppress input to output leakage. After filtering, the measured RMS
amplitude is expressed relative to the amplitude resulting from the reference measurement.
If the measurement is made at the digital output of the EUT, then the signal should be filtered with a
notch filter at the frequency of the applied stimulus unless the input signal exceeds the folding
frequency. The RMS amplitude of the remaining signal is then measured and is expressed relative to
the amplitude resulting from the reference measurement.
The results are presented for both channels as a graph in dB relative to the output reference
amplitude.
3.2.3.2 Susceptibility to RF interference
This test is still 'under consideration' by the AES, and is not yet included in the AES17
standard.
3.2.3.3 Overload behaviour
Applies to:
EUTs with analogue inputs.
Aim:
To identify undesirable overload behaviour in A/D converters, a condition commonly called
'rollover'.
Method
The unweighted THD+N is measured for a 997Hz sinusoidal input to the
EUT
at +3
dBFS
and
–3dBFS, the result is the ratio of the two results (i.e. the difference in dB) and is expressed in dB for
both channels.