because the spot frequency levels that the tolerance is applied to are affected by the
normalisation (ie the levels that are checked against the tolerance are always the same as
the levels that are printed). A tolerance which has been defined assuming 1kHz
normalisation might fail every value if given absolute levels instead of normalised levels.
To cater for such possibilities the normalisation can be specified within the tolerance
definition and this overrides the configuration J setting to ensure that the correct levels are
compared with the tolerance. The ! character is used to force the normalisation to
absolute (
!0), 315Hz (!1), 400Hz (!2) or 1kHz (!3), regardless of the configuration J
setting (and the V segment). This can be placed anywhere within the tolerance definition,
but it is conventionally placed after the tolerance title (as shown in table 5.3).
! character in tolerance
5.5 Printout Format Printout format Format of printout Comments on printouts Printout comments % distortion tolerances
In addition to the pass/fail features the tolerance strings can also be used to control the
format of test printouts, albeit in a limited way.
Since the tolerance strings are free format, it is possible to include extra information
(numbers and symbols only) which will appear on the results printout next to the relevant
values. One use is to make the LA102 print distortion tolerances in % as well as dB, as
explained in section 5.4. It is also useful to list the target or expected values for user level
results (see segment K, section 4.13). For example, suppose segment K is being used to
generate the levels -20,-25,-30,-35,-40 and -45dB, a tolerance could be defined to list
these values without actually testing them by preceding each target value with an = sign.
When the tolerance system encounters any invalid character (such as =) it will ignore the
rest of the tolerance string, but still print it. For this example, the tolerance would be:
K =-20,=-25,=-30,=-35,=-40,=-45
Sometimes a much simpler printout is required than that normally provided, perhaps only
listing one distortion value and one crosstalk value, and a reduced frequency response list.
This may be to enable more results to be printed on a single sheet, or perhaps because the
other values are not needed and an uncluttered printout is required. In some cases it may
be possible to choose a more appropriate segment and this will also reduce the test time
(segment F measures distortion at 6 frequencies whereas segment D only measures it at
3). Where there is no shorter segment it is possible to suppress particular results values
by putting a slash character (/) in the corresponding tolerance string.
For example, the following tolerance definition:
/ to suppress printout values Suppress printout values
N-40,/,/ C/,,,?,/,?
will apply a tolerance of -40dB to the CCIR peak weighted noise result, and suppress the
printing of unweighted and mean noise. It will also suppress the 40Hz, 100Hz, 315Hz
and 6.3kHz crosstalk results and only print the 1kHz and 10kHz values. Note that the
?
95
5. Tolerance Testing
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