Specifications

2.10
Applications Manual
© 2003-2005 Prism Media Products Ltd
Revision 1.11Prism Sound dScope Series III
Used in
Input for full-scale amplitude
and
Maximum input amplitude
tests.
This search routine looks for the input amplitude that causes one of three conditions: For systems
where the digital signal is accessible, it finds the input level that causes 0dBFS at 997Hz. For
systems where the digital signal is not accessible or cannot be made to reach 0dBFS, it looks for the
level that causes 1% distortion or 0.3dB compression, which-ever comes first. It does this in two
stages. The first stage is to ramp the level fed into the unit from a level 12dB below a defined starting
level (typically the input D/A Line-up) in 3dB steps. When any of the conditions are met, the search
switches to a binary search routine between the last two input levels to narrow down the search
further. The tolerances are set in the script and are to within 0.01dB for full scale amplitude, 0.01 %
for THD+N and 0.01dB for compression . The routine then returns the level that caused the condition
and which condition was met. When measuring the second channel of a two channel device, the first
stage is skipped and the search goes directly to the binary search in a range +/-3dB of the value
found for the first channel.
If any of the conditions are already breached at the starting point, the search cannot complete and a
message will display. Usually this can be remedied by adjusting the input D/A line-up figure.
Sometimes a message will display that the conditions were not met within the search range. This
may mean that the dScope is not capable of generating sufficient voltage to cause any of the
conditions to be met, but may also occur if there is a set-up problem. Another error condition occurs
when the binary search does not converge. This can happen with soft knee compression or
compression with long release times that do not allow the search routine to settle correctly. It can
also happen if there is a big difference between the channels when measuring channel B.
Find the maximum output amplitude
Used in
Output amplitude at full scale
,
Maximum output amplitude
and
Maximum signal level vs frequency
tests.
This is essentially identical in principle to the Find the Maximum input amplitude routine described
above, only it returns the output level rather than the input level. The same type of error messages
are generated.
Find the input that causes a set output level
Used in
Signal-to-noise ratio or noise in the presence of signal
(-60dBFS search routine) and
Low level noise modulation
(-40dBFS search routine).
This routine is also used when searching for
digital full scale signals (ie, when finding
Input for full-scale amplitude
with a EUT with a digital output.)
This search routine looks for the input level that causes a specified output level. It is considerably
simpler than the routines described above. It also uses two stages. The first stage finds the required
level within 3 dB and the second narrows it down to within 0.01dB. The first stage works by making
the assumption that the unit's gain can be found by subtracting the input D/A Line-up from the output
D/A Line-up and sets the starting point for input based on this. It then steps in 3dB steps up or down
depending on the result of the measured output level. When the level is found within 3dB, it switches
to a binary search until the required level is found. This routine may fail if there is any compression
with a long release time.
3.2.3 Input characteristics
The Input characteristics tests are arranged in the following subsections, which correspond to the
equivalent subsections of the AES17 standard:
Suppression of alias components
Susceptibility to RF interference
Overload behaviour
Input for full-scale amplitude
Maximum input amplitude
Input logarithmic-gain stability
Digital audio input format
Jitter susceptibility