The segments may be specified in any order, and any segments that have the same
tolerance specification (eg R and S, or T and V) can be specified together by putting the
segment letters together. If any tolerance for a particular value in a segment is omitted
the tolerance for the previous value is assumed. For example, for distortion segment D,
the specification should start with a ‘D’ and be followed by a tolerance for 100Hz
distortion, 1kHz distortion and 6.3kHz distortion respectively. Space characters may be
inserted to make the tolerance more readable (a space before each segment letter is
strongly recommended). It is also possible to give the tolerance a title by putting a
message in quotes at the start of the definition. For example:
"DEMO" TV±.5<.1 D-60,-70,-65 YZ±20,,,±40
The tolerance title is ‘DEMO’ and this will appear on the printout and in the configuration
menu. The measured test level (segment T or V) must be within ±0.5dB of 0dBu and the
difference between channels less than 0.1dB. There is a -60dB upper limit for 100Hz
distortion, -70dB for 1kHz and -65dB for 10kHz. Phase (segment Y or Z) must be within
±20° of 0° at 40, 100 and 1kHz and within ±40° at 6.3k, 10k and 15kHz (the missing
tolerance strings default to the previous tolerance specification in the segment).
Before programming tolerance definitions into the LA102 it is a good idea to run a
sequence on the system for which the tolerance is being produced and print the results.
The proposed tolerance strings can then be written in beside each measurement and used
to produce the tolerance definition. Once the full definition has been programmed into
the LA102, the results can be printed again, with the tolerance applied, to ensure that the
tolerance definition is correct and that it agrees with the proposed version.
Distortion tolerances must be specified in dB regardless of the printout setting, but users
who prefer distortion results in % can put the equivalent percentage after the dB value,
using an "=" symbol as a separator (see section 5.5). Only the dB value is used, as text
following an "=" symbol is ignored up to the next comma, but it will appear on the
printout. For example:
D-50.5=0.3%, -60=0.1%, -80=0.01%
W&F and speed values must be in % and phase in degrees. All other values are specified
in dB. Frequency response tolerances always refer to the normalised levels of the
tabulated frequencies. Examine the built in tolerances for more examples.
A question mark (?) can be entered as a tolerance string to indicate that there is no
tolerance for that value and the tolerance column is left blank on the printout, eg
C-17,?,,-36,?,-32 will specify a tolerance for 40, 1k and 10kHz crosstalk, but will indicate
a "Don't Care" condition for 100, 315 or 6.3kHz.
Some care is needed when using a tolerance to check the frequency response results
94
5. Tolerance Testing
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